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Title: USFWS Circular 16: Migration of Birds (1950)
Author: Lincoln, Frederick C.
Language: English
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BIRDS (1950) ***
Transcriber's Note
Emphasized text is denoted by _Italics_ and =Bold=.
[Illustration]
MIGRATION of BIRDS
[Illustration]
CIRCULAR 16
FISH AND WILDLIFE SERVICE
UNITED STATES DEPARTMENT OF THE INTERIOR
MIGRATION of BIRDS
[Illustration]
By FREDERICK C. LINCOLN
_Biologist_
Illustrated by BOB HINES
CIRCULAR 16
UNITED STATES DEPARTMENT OF THE INTERIOR, Oscar L. Chapman, _Secretary_
FISH AND WILDLIFE SERVICE, Albert M. Day, _Director_
[Illustration]
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1950
For sale by the Superintendent of Documents, Washington 25, D. C.
Price 30 cents
Contents
Page
The mystery of migration 4
Advantages of migration 6
The origin of migration 7
Northern ancestral home theory 8
Southern ancestral home theory 8
Theory of photoperiodism 9
Theory of continental drift 11
When birds migrate 11
Movements of species and groups 12
Nocturnal and diurnal migration 15
How birds migrate 18
Speed of flight and speed of migration 18
Altitude at which birds travel 26
Orientation 28
Segregation during migration 31
Where birds migrate 34
Short and undetermined migrations 34
Variable migrations within species 35
Fall flights not far south of breeding ranges 37
Long-distance migrations 38
Routes of migration 41
Wide and narrow migration lanes 42
The fly ways 46
Atlantic oceanic route 48
Atlantic coast route and tributaries 53
Mackenzie Valley--Great Lakes--Mississippi Valley Route and
tributaries 60
Great Plains--Rocky Mountain routes 62
Pacific coast route 63
Pacific oceanic route 66
Arctic routes 68
Evolution of migration routes 70
Vertical migration 72
Vagrant migration 73
Perils of migration 75
Storms 75
Aerial obstructions 76
Exhaustion 78
Influence of the weather on migration 80
Problems of migration 81
Banding studies 81
Movements of residents 82
Migration of the white-throated sparrow 84
Migration of the yellow-billed loon 84
Conclusions 85
Appendix I--List of birds mentioned in the text 87
Appendix II--Bird banding 92
Bibliography 94
Index 99
MIGRATION of BIRDS
When the birds that have nested in our dooryards and those that have
frequented the neighboring woods, hills, and marshes leave us in the
fall, the question naturally comes to mind: Where do they go? This,
however, is only one small part of the question as we also wonder:
Will the same ones return next spring to their former haunts? What
dangers will they face on their round-trip flight and while in their
winter homes? These and other questions on the migratory habits
of most species of Northern Hemisphere birds puzzle all who are
interested in them, whether it be the farmer who profits by their
tireless warfare against the weed and insect pests of his crops,
the bird student who enjoys an abundance and variety of feathered
inhabitants about him, or the hunter who wants a continuation from
year to year of the sport of wildfowling. Lack of information on the
subject may mean the loss of an important resource by unconsciously
letting it slip from us, as ignorance might be responsible for
inadequate legal protection for such species as might urgently
need it. More general knowledge on the subject will aid in the
perpetuation of the various migrants, the seasonal habitats of some
of which are in grave danger from man's utilization, sometimes
unwisely, of the marsh, water and other areas that were formerly
homes for birds.
The migrations of birds were probably among the first natural
phenomena to attract the attention and intrigue the imagination of
man. Recorded observations on the subject date back nearly 3,000
years, to the times of Hesiod, Homer, Herodotus, Aristotle, and
others. In the Bible there are several references to the periodic
movements of birds, as in the Book of Job (39:26), where the inquiry
is made: "Doth the hawk fly by Thy wisdom and stretch her wings
toward the south?" Jeremiah (8:7), wrote: "The stork in the heavens
knoweth her appointed time; and the turtle [dove], and the crane, and
the swallow, observe the time of their coming." And the flight of
quail that saved the Israelites from starvation in their wanderings
in the wilderness of Sinai is now recognized as a vast movement of
migratory quail between their breeding grounds and their winter home
in Africa.
Throughout the ages the return flights of migratory birds have
been important as a source of food after a lean winter and as the
harbinger of a change in season. The arrival of certain species
has been heralded with appropriate ceremonies in many lands, and
among the Eskimos and other tribes the phenomenon to this day is
the accepted sign of the imminence of spring and of warmer weather.
The pioneer fur traders in Alaska and Canada offered rewards to the
Indian or Eskimo who saw the first goose of the spring, and all
joined in jubilant welcome to the newcomer.
As the North American Continent became more thickly settled, the
large flocks of ducks and geese that always had been hunted for food
became objects of the enthusiastic attention of an increasing army
of sportsmen. Most of the nongame species were found to be valuable
also as allies of the farmer in his never-ending warfare against weed
and insect pests. The need for laws protecting the valuable game
and nongame birds and for regulating the hunting of the diminishing
game species followed as a natural course. In the management of this
wildlife resource it has become obvious that continuous studies
must be made of the food habits of the various species, their
environmental needs, and their travels. Hence bird investigations are
made by the Fish and Wildlife Service, the bureau charged by Congress
under the Migratory Bird Treaty Act with the duty of protecting those
species that in their yearly journeys pass back and forth between the
United States and Canada, and between the United States and Mexico.
For more than half a century the Fish and Wildlife Service and
its predecessor, the Biological Survey, have been collecting data
on the interesting and important phenomenon of the migration of
North American birds. The field men of the Service have gathered
information concerning the distribution and seasonal movements of
the different species in many extended areas, from the Arctic coast
south to the pampas of Argentina. Supplementing these investigations
is the work of hundreds of volunteer ornithologists and bird students
throughout the United States and Canada, who each year, spring and
fall, forward to the Service reports on the migrations as observed in
their respective localities. Added to the mass of data thus assembled
is a rapidly growing recovery file of marked individuals. These
data, together with other carded records gleaned by the Fish and
Wildlife Service from a vast literature, constitute a series of files
that now contain well over 3,000,000 entries, easily the greatest
existing accumulation of information pertaining to the distribution
and movements of North American birds. Not only do the facts thus
assembled form the basis of regulatory action for the protection
of the birds, but they also make it possible to publish scientific
accounts of the ranges and migrations of the different species. They
furnish the basis of this bulletin.
The several important bird-protective measures adopted by State and
Federal Governments, particularly those having as their objectives
the conservation of the migratory song, insectivorous, and game
species, can be effective only if they have intelligent public
support. To increase such support, information must be more generally
available on that little understood but universally fascinating
subject of bird migration. A brief presentation of facts on the
migratory habits of the birds scientifically gathered by the Fish
and Wildlife Service over many years, will be helpful to bird-study
classes, to conservation organizations, and to farmers and others
individually interested in the welfare of the birds.
In addition to his original investigations in the field and in the
files of the Fish and Wildlife Service, the author has made free use
of the writings of many other students of the subject. To all of
these grateful acknowledgment is made.
_The Mystery of Migration_
Of observers whose writings are extant, Aristotle, naturalist and
philosopher of ancient Greece, was one of the first to discuss the
subject of bird migration. He noted that cranes traveled from the
steppes of Scythia to the marshes at the headwaters of the Nile,
and that pelicans, geese, swans, rails, doves, and many other
birds likewise passed to warmer regions to spend the winter. In
the earliest years of the Christian era, the elder Pliny, Roman
naturalist, in his Historia Naturalis, repeated much of what
Aristotle had said on migration and added comments of his own
concerning the movements of the European blackbird, the starling, and
the thrushes.
In spite of the keen perception shown in some of his statements
Aristotle also must be credited with the origin of some superstitious
beliefs that persisted for several centuries. One of these, that
of hibernation, became so firmly rooted that Dr. Elliott Coues
(1878),[1] one of America's greatest ornithologists, listed the
titles of no less than 182 papers dealing with the hibernation
of swallows. The hibernation theory accounted for the autumnal
disappearance of certain species of birds by having them pass into
a torpid state and so remain during the cold season, hidden in
hollow trees, caves, or in the mud of marshes. Aristotle ascribed
hibernation not only to swallows, but also to storks, kites, doves,
and others. Some early naturalists wrote fantastic accounts of the
flocks of swallows that allegedly were seen congregating in the
marshes until their accumulated weight bent into the water the
reeds on which they clung and thus submerged the birds. It was even
recorded that when fishermen in northern waters drew up their nets
they sometimes had a mixed "catch" of fish and hibernating swallows.
Clarke (1912) quotes Olaus Magnus, Archbishop of Upsala, who in 1555
published a work entitled "Historia de Gentibus Septentrionalis et
Natura," wherein he observed that if swallows so caught were taken
into a warm room they would soon begin to fly about but would live
only a short time.
[1] Publications referred to parenthetically by date are listed
in the Bibliography, p. 94.
The hibernation theory survived for more than 2,000 years and, until
the winter home of the chimney swift was discovered in 1944 through
the recovery of banded individuals, it was occasionally repeated
by credulous persons to account for the sudden disappearance of
the immense flocks that each autumn gather in southern Georgia and
northern Florida. Although the winter range is still unknown in
fullest detail, Lincoln (1944b) has shown that some of these birds
spend the winter season in northeastern Peru.
Although the idea that hibernation is a regular feature of the life
cycle of birds is no longer accepted for any species, recognition
must be accorded the observations of Edmund C. Jaeger of Riverside
College, Riverside, Calif. (1949). Earlier (1948), he had given a
brief account of the behavior of a poor-will found during the winter
of 1946-47 in the Chukawalla Mountains of the Colorado Desert,
Calif., and which was in a state of profound torpidity.
What was presumably the same individual was found in the same rock
niche in a comatose condition on November 26, 1947. Beginning on
December 30, 1947, rectal temperatures were taken every 2 weeks, the
last on February 14, 1948. The temperature dropped from 67.6° on the
first date to 64.4° on January 18 and February 1, recovering to 65.8°
on the late date of record. The weight decreased from 45.61 grams on
January 4 to 44.56 grams on February 14. An attempt to detect heart
beat by the use of a medical stethoscope was negative. No movement of
the chest walls could be detected and no moisture could be collected
on a cold mirror placed in front of the nostrils. Strong light aimed
directly into the pupil resulted in no response, not even an attempt
to close the eyelid. No waste matter was passed during the entire
period of observation and all evidence indicated that the bird was in
an exceedingly low state of metabolism.
This bird was banded on January 5, 1948, with a Service band and
was back in the same rock niche on November 24, 1948, certainly
the second and probably the third season of return to this exact
point. It was there on December 5, 1948, but 2 weeks later it had
disappeared, probably the victim of some predator or an inquisitive
human. Professor Jaeger reports that the Hopi Indians call the
poor-will "Holchko," the sleeping one.
Aristotle also was the originator of the theory of transmutation,
basing it upon the fact that frequently one species will arrive
from the north just as another species departs for more southerly
latitudes. From this he reasoned that although it was commonly
believed that such birds were of two different species, there really
was only one, and that this one assumed the different plumages to
correspond with the summer and winter seasons.
Probably the most remarkable theory that has been advanced to account
for migration is contained in a pamphlet mentioned by Clarke (1912:
V. I, 9-11) as published in 1703 under the title: "An Essay Toward
the Probable Solution of this Question: Whence come the Stork and
the Turtle, the Crane, and the Swallow, when they Know and Observe
the Appointed Time of their Coming." It was written "By a Person of
Learning and Piety," whose "probable solution" was that migratory
birds flew to the moon and there spent the winter.
Some peoples, who easily accepted the migratory travels of the larger
birds, were unable to understand how the smaller species, some of
them notoriously poor fliers, could make similar journeys. They
accordingly conceived the idea that the larger species, as the storks
and cranes, carried their smaller companions as living freight. In
some of the Mediterranean countries, it is still believed that these
broad-pinioned birds serve as aerial transports for the hosts of
small birds that congregate upon the shores awaiting opportunity for
this kind of passage to their winter homes in Africa. Similar beliefs
have been found among some tribes of North American Indians.
_Advantages of Migration_
Before presenting some of the present theories concerning the origin
of bird migration, it seems well to consider briefly the ends that
are served by this annual round trip between breeding grounds and
winter quarters. It is apparent that the migratory habit enables a
species to enjoy the summers of northern latitudes while avoiding the
severity of the winters. In other words, migration makes it possible
for some species to inhabit two different areas during the seasons
when each presents favorable conditions. In the performance of its
reproductive duties, every pair of birds requires a certain amount of
territory, the extent of which varies greatly in different species.
Generally, however, this territory must be large enough to provide
adequate food, not only for the parent birds, but also for the lusty
appetites that come into being with the hatching of the eggs. Thus,
if all birds were to remain constantly either in tropical or in
temperate regions, there would be intolerable overcrowding during the
breeding season. By the spring withdrawal to regions uninhabitable
earlier in the year, the migrants are assured of adequate space and
ample food upon their arrival in the winter-freed North, and it may
be assumed that the nonmigratory species that are resident in the
South are also benefited by the departure of the migrants.
Nevertheless, it cannot be said that the winter or summer area of
every species is entirely unsuited to its requirements at other
seasons, for some individuals pass the winter season in areas that
are frequented only in summer by other individuals of their species.
Such species have extensive breeding ranges, presenting wide climatic
variations, so that some individuals may actually be resident in a
region where others of their kind are present only in winter.
The tendency of some birds to move southward at the approach of
winter is not always due to the seasonal low temperatures, since
experiments have demonstrated that many of our summer insect feeders,
when confined in outdoor aviaries, comfortably withstand temperatures
far below zero. The main consideration is the depletion of the food
supply, caused either by the disappearance or the hibernation of
insects, or by the mantle of snow or ice that prevents access to the
seeds and other forms of food found on or close to the ground or
submerged in water. Possibly also the shortened hours of daylight
materially restrict the ability of the birds to obtain sufficient
food at a time when the cold requires an increased supply to maintain
body heat. It is noteworthy that some of our smaller birds, such
as the chickadees, have no fear of Arctic weather, as their food
supplies are entirely arboreal and so are always available. Also,
when there is a good supply of food in the form of pine and spruce
seeds, nuthatches and crossbills will remain through the winter in
Canadian woods. When these birds appear abundantly in winter at
points in southern latitudes, it may be concluded that there is a
shortage of their food in the North.
_The Origin of Migration_
Migration has long since become a definite hereditary habit that
recurs in annual cycles, probably because of physiological stimulus
associated with the reproductive period. Its origin is locked in the
ages of geologic time, but by study of the history of how birds came
to occupy their present ranges, information becomes available from
which reasonable theories may be developed and explored. The two that
are most commonly accepted are diametrically opposed to each other.
=Northern ancestral home theory=
According to one of these hypotheses, in earlier ages nonmigratory
birds swarmed over the entire Northern Hemisphere. At that time the
conditions of food and habitat were such as to permit them to remain
in their haunts throughout the year, that is, the entire northern
area then afforded the two important avian requirements--suitable
breeding conditions, and year-long food supply. This is the condition
today in the Tropics, and it is noteworthy that, as a rule, tropical
birds do not perform migrations. Gradually, however, in the Northern
Hemisphere the glacial ice fields advanced southward, forcing the
birds before them, until finally all bird life was concentrated
in southern latitudes. As the ages passed the ice cap gradually
retreated, and each spring the birds whose ancestral home had been in
the North endeavored to return, only to be driven south again at the
approach of winter. As the size of the ice-covered area diminished
the journeys made became ever longer until eventually the climatic
conditions of the present age became established and with them the
habit of migration.
Thus, this theory supposes that today migratory birds follow the path
of a great racial movement that took place in a distant past and was
associated with the advances and recessions of the ice. The actions
of the birds themselves lend some support to this theory, as every
bird student has noted the feverish impatience with which certain
species push northward in spring, sometimes advancing so rapidly upon
the heels of winter that they perish in great numbers when overtaken
by late storms. It is probable that at this season the reproductive
impulse is a determining factor in driving the birds to their
northern breeding grounds.
=Southern ancestral home theory=
The opposing theory is simpler in some respects and supposes that the
ancestral home of all birds was in the Tropics and that, as all bird
life tends to overpopulation, there was a constant effort to seek
breeding grounds where the competition would be less keen. Species
that strove for more northern latitudes were kept in check by the ice
and were forced to return southward with the recurrence of winter
conditions. Gradually, as the ice retreated, vast areas of virgin
country became successively suitable for summer occupancy, but the
winter habitat remained the home to which the birds returned after
the nesting season. It is a fact that some species spend very little
time on their breeding grounds; the orchard oriole, for example,
spends only 2½ months in its summer home, arriving in southern
Pennsylvania about the first week in May and leaving by the middle of
July.
Both of these theories assume that migration is an ingrained habit,
but both have been criticized on biological and geological grounds,
so neither should be accepted without qualification as definitely
accounting for the origin of bird migration. It is apparent, however,
that whether the ancestral home of any species was at the northern or
southern limits of its present range, or even in some intermediate
region, the search for favorable conditions under which to breed in
summer and to feed in winter has been the principal factor underlying
the origin of migration.
=Theory of photoperiodism=
A modern view based on studies of living behavior, suggests also that
there is good reason for believing that migration is an annually
induced movement. If such be true then the theory of photoperiodism
as propounded by some recent investigators should receive some
consideration.
This theory holds as its major premise that quantity of light and
length of day are the stimulating causes of migration. Its proponents
urge that migration is a phenomenon far too regular to be created
anew each season merely under stress of circumstances, such as need
for food; and that it begins before the necessity for a change in
latitude becomes at all pressing. Swallows, nighthawks, shore birds,
and others may start their southward movement while the summer food
supply in the North is at peak abundance; while robins, bluebirds,
and others may leave an abundant food in the South in spring and
press toward northern points when food supplies there are almost
entirely lacking and when severe cold and storms are likely to cause
their wholesale destruction. The regularity of arrival and departure
is one of the most impressive features of migration, and since birds
travel in almost strict accordance with the calendar, the proponents
of the theory ask: "What phenomenon to which we may attribute the
stimulating impulse occurs with such precise regularity as the
constantly increasing amount of light in spring?"
Experimental work has abundantly demonstrated the effect of increased
light upon the growth, flowering, and fruiting of plants. Similarly,
experiments with the common junco or snowbird reported by Rowan (1931:
121), resulted in increased development of the sexual organs by
the end of December, although the birds were confined in outdoor
aviaries in Canada, and had been exposed to temperatures as low as
-44° F. From the first of November until early in January, the juncos
were subjected to ever-increasing light, supplied in the aviaries by
electric bulbs. As regards illumination, they were thus artificially
provided with conditions approximating those of spring. At the close
of this period, it was found that the sexual organs of the birds had
attained the maximum development normally associated with spring.
With gradual reduction of the lighting over a period of little more
than 1 month, the organs returned to their normal winter condition.
After a consideration of all evidence, including the fact that no
ultra-violet rays were used, it was concluded that the explanation
lay in the increased exercise taken during the periods of increased
light. A simple test whereby certain birds were forced by mechanical
means to take more exercise, the light being so reduced that there
was merely sufficient glow for them to see the advancing mechanism
that forced them into movement, showed that the rate of development
of the sexual organs exactly paralleled that in the birds that were
exposed to extended periods of illumination in the outdoor aviaries.
Other features in this experiment--such as the behavior of the birds
themselves--also indicated that more activity due to increased light
is the governing cause of the spring development of the sexual
organs. If this development be accepted as a controlling cause of
migration, then this experiment must be recognized as of great
importance.
Upon closer analysis, however, it is found that this theory, like
those before discussed, is open to serious objections. First, some of
our summer residents that migrate south for the winter do not stop
in equatorial regions, where they might find the periods of day and
night about equally divided, but push on beyond, some penetrating as
far south as Patagonia. Also it might be asked: "If the lengthening
day is the stimulating factor, why should our summer birds wintering
in the Tropics ever start northward, as in their winter quarters
the variation in the length of day from winter to summer is
imperceptible?" Like all the other theories advanced, this also, as
at present understood, is subject to unanswered criticism.
=Theory of continental drift=
The theory of continental drift postulates an original northern land
mass, called Laurasia, and a southern one, called Gondwana. According
to this concept, each eventually broke into several segments which
eventually became the present continents. It is further assumed that
occasionally Laurasia and Gondwana drifted close to one another or
were at times in actual contact. On the basis of this geological
theory, Wolfson (1940) has attempted to explain the migrations of
some species of birds from one hemisphere to the other, as, for
example, the Greenland wheatear, Arctic tern, and several shore
birds (turnstone, sanderling, knot, golden plover, and others).
Acceptance of this hypothesis requires abandonment of the belief that
the development of migration was the result of useful ends that were
served thereby, and in its place, to give approval to the idea that
migration was merely "the natural consequence of an inherent behavior
pattern responding to the drifting of continental masses."
It is a strange fact that although almost all professional
paleontologists are agreed that existing data oppose the theory of
continental drift, those who support it contend that their case is
strengthened by these same data. If, in the geologic history of the
earth, there was any such thing as continental drift, it appears
from the evidence available that it was before the Cretaceous
period, estimated to have been about 70,000,000 years ago. Birds had
then evolved but those known from fossil remains were of extremely
primitive types such as Hesperornis and Ichthyornis. There is no
evidence of the existence in that period of any birds that were
even closely related to any of those now living. Accordingly, it is
difficult to believe that the migratory patterns of existing species
have been determined by events that, if they did take place, were at
least 70,000,000 or more years ago.
_When Birds Migrate_
It is known that at any given point many species leave in the fall
and return in the spring. Since banding has had such wide application
as a method of study, it is known also that in some species one of
the parent birds (rarely both) frequently returns and nests in the
tree, bush, or box that held its nest in the previous season. One
ordinarily thinks of the world of birds as quiescent during two
periods each year, at nesting time, and in winter. For individuals
this is obviously the case, but when the entire avifauna of the
continent is considered it is found that there are at almost all
periods some latitudinal movements.
=Movements of species and groups=
Some species begin their fall migrations early in July and in some
parts of the country distinct southward movements can be detected
from then until the beginning or middle of winter. For example,
many shore birds start south in the early part of July, while the
goshawks, snowy owls, redpolls, Bohemian waxwings, and many others
do not leave the North until forced to do so by the advent of severe
winter weather, or by lack of the customary food. Thus an observer in
the northern part of the United States may record an almost unbroken
southward procession of birds from midsummer to winter, and note
some of the returning migrants as early as the middle of February.
While on their way north, purple martins have been known to arrive
in Florida late in January and, among late arrivals, the northern
movement may continue into the first week of June. In some species
the migration is so prolonged that the first arrivals in the southern
part of the breeding range will have performed their parental duties
while others of that species are still on their way north.
A study of these facts indicates that sometimes there exists a very
definite relationship between what we may term northern and southern
groups of individuals of the same species. A supposition is that
for a species with an extensive latitudinal breeding range, and
which has a normal migration, those individuals that nest farthest
south migrate first and proceed to the southern part of the winter
range; those that occupy the central parts of the breeding range
migrate next and travel to regions in the winter range north of
those occupied by the first group; and finally the individuals
breeding farthest north are the last to start their autumn migration
and they remain farthest north during the winter. In other words,
this theory supposes that the southward movement of the species is
such that the different groups maintain their relative latitudinal
position with each other. The black and white warbler furnishes
an example. The breeding range of this bird extends west and
northwest from northern Georgia and South Carolina to New Brunswick,
extending also in a western and northwestern direction as far as
Great Bear Lake in northwestern Canada (fig. 1). It spends the
winter in southern Florida, the West Indies, central Mexico, Central
America, and northwestern South America. In the southern part of
its breeding range it is nesting in April, but those that summer in
New Brunswick do not reach their nesting grounds before the middle
of May. Therefore, about 50 days are required for these northbound
birds to cross the breeding range, and if 60 days be allowed for
nest building, egg laying, incubation, care of young, and molt, they
would not be ready to start southward before the middle of July
(fig. 2.). Then another 50-day trip south, and the earliest migrants
from the northern areas would reach the Gulf Coast in September.
But both adults and young have been observed at Key West, Fla., by
the middle of July, and on the northern coast of South America by
August 21. Since the birds at Key West were fully 500 miles south of
the breeding range, it is evident that they must have come from the
southern part of the nesting area.
[Illustration: _Figure 1._--Summer and winter homes of the black
and white warbler, a very slow migrant as the birds nesting in the
northern part of the country take 50 days to cross the breeding
range. The speed of migration is shown in figure 2. (See p. 14.)]
[Illustration: _Figure 2._--Isochronal migration lines of the black
and white warbler, showing a very slow and uniform migration. These
birds apparently advance only about 20 miles a day in crossing the
United States. (See p. 13.)]
Many similar cases might be mentioned, such as the black-throated
blue warblers, which are still observed in the mountains of Haiti in
the middle of May, when others of this species are en route through
North Carolina to breeding territory in New England or have even
reached that region. Redstarts and yellow warblers, evidently the
more southern breeders, are seen returning southward on the northern
coast of South America just about the time that the earliest of
those breeding in the North reach Florida on their way to winter
quarters.
=Nocturnal and diurnal migration=
When one recalls that most birds appear to be more or less helpless
in the dark, it seems remarkable that many should select the night
hours for extended travel. Among those that do, however, are the
great hosts of shore birds, rails, flycatchers, orioles, most of
the great family of sparrows, the warblers, vireos, and thrushes,
and in fact, the majority of small birds. That it is common to find
woods and fields on one day almost barren of bird life, and on the
following day filled with sparrows, warblers, and thrushes, would
indicate the arrival of migrants during the night. Sportsmen sitting
in their "blinds" frequently observe the passage of flocks of ducks
and geese, but great numbers of these birds also pass through at
night, the clarion call of the Canada goose, or the conversational
gabbling of a flock of ducks being common night sounds in spring and
fall in many parts of the country. The sibilant, nocturnal calls of
the upland plover or Bartramian sandpiper and of other shore birds
during their spring and fall flights form vivid memories in the minds
of many students of migration. Observations made with telescopes
focused on the full moon have shown processions of birds, one
observer estimating that birds passed his point of observation at the
rate of 9,000 an hour, which gives some indication of the numbers of
birds that are in the air during some of the nights when migration
is at its height. While the steady night-long passage of migratory
birds has been recorded, the bulk of the flocks pass during the
earlier hours of the evening and toward daylight in the morning, the
periods from 8 o'clock to midnight and from 4 to 6 a. m. seeming to
be favorite times for nocturnal flight.
It has been claimed, with some reason, that small birds migrate
by night the better to avoid their enemies, and that most of the
nocturnal travelers are those that are naturally timid, sedentary,
or feeble-winged. To a certain extent this may be true as included
in this group are not only such weak fliers as the rails but also
the small song and insectivorous birds such as the wrens, the small
woodland flycatchers, and other species which, living habitually more
or less in concealment, are probably much safer making their flights
under the protecting cloak of darkness. Nevertheless, it must be
remembered that night migrants include also the snipe, sandpipers,
and plovers, birds that are always found in the open, and are among
the more powerful fliers, some of them making flights of more than
2,000 miles across the ocean.
Night travel is probably best for the majority of birds chiefly
from the standpoint of feeding. Digestion is very rapid in birds
and yet the stomach of one killed during the day almost always
contains food. To replace the energy required for long flight, it is
essential that food be obtained at comparatively short intervals, the
longest of which in most species is during the hours of darkness.
If the smaller migrants were to make protracted flights by day they
would be likely to arrive at their destination at nightfall almost
exhausted, but since they are entirely daylight feeders, they would
be unable to obtain food until the following morning. This would
delay further flights and result in great exhaustion or possibly
even death were they so unfortunate as to have their evening arrival
coincident with unusually cold or stormy weather. Traveling at night,
they pause at daybreak and devote the entire period of daylight to
alternate feeding and resting. This permits complete recuperation and
resumption of the journey at nightfall.
Many species of wading and swimming birds migrate either by day or
night, as they are able to feed at all hours, and are not accustomed
to seek safety in concealment. Some diving birds, including ducks
that submerge when in danger, sometimes travel over water by day and
over land at night. The day migrants include, in addition to some
of the ducks and geese, the loons, cranes, gulls, pelicans, hawks,
swallows, nighthawks, and the swifts. All of these are strong-winged
birds. The swifts, swallows, and nighthawks (sometimes called
bullbats) feed entirely on flying insects, and use their short,
weak feet and legs only for grasping a perch during periods of rest
or sleep. Thus they feed as they travel, the circling flocks being
frequently seen in late summer working gradually southward. Years ago
before birds of prey were so thoughtlessly slaughtered, great flocks
of red-tailed. Swainson's, and rough-legged hawks might be seen
wheeling majestically across the sky in the Plains States, and in the
East the flights of broad-winged. Cooper's, and sharp-skinned hawks
are still occasionally seen. To the birds of prey and possibly to the
gulls also, a day's fasting now and then is no hardship, particularly
since they frequently gorge themselves to repletion when opportunity
is afforded.
[Illustration: _Figure 3._--Migration of the cliff swallow, a day
migrant that instead of flying across the Caribbean Sea as does the
blackpolled warbler (see fig. 6), follows around the coast of Central
America, where food is readily obtained. (See p. 25.)]
An interesting comparison of the flights of day and night migrants
may be made through a consideration of the spring migrations of the
blackpolled warbler and the cliff swallow. Both spend the winter
in South America, at which season they are neighbors. But when the
impulse comes to start northward toward their respective breeding
grounds, the warblers strike straight across the Caribbean Sea
to Florida (fig. 6), while the swallows begin their journey by a
westward flight of several hundred miles to Panama (fig. 3.). Thence
they move leisurely along the western shore of the Caribbean Sea
to Mexico, and continuing to avoid a long trip over water, they
go completely around the western end of the Gulf of Mexico. This
circuitous route adds more than 2,000 miles to the journey of the
swallows that nest in Nova Scotia. The question may be asked: "Why
should the swallow select a route so much longer and more roundabout
than that taken by the blackpolled warbler?" The simple explanation
is that the swallow is a day migrant while the warbler travels at
night. The migration of the warbler is made up of a series of long,
nocturnal flights, alternated with days of rest and feeding in
favorable localities. The swallow, on the other hand, starts its
migration several weeks earlier and catches each day's ration of
flying insects during a few hours of aerial evolutions, which at the
same time carry it slowly in the proper direction. Flying along the
insect-teeming shores of the Gulf of Mexico, the 2,000 extra miles
that are added to the migration route are but a fraction of the
distance that these birds cover in pursuit of their daily food.
Although most of our smaller birds make their longest flights at
night, close observation will show that travel is continued to some
extent by day. This is particularly true during the latter half of
a migratory season when the birds show evidence of an overpowering
desire to hasten to their breeding grounds. At this time flocks of
birds while feeding maintain a movement in the general direction of
the seasonal journey. Sometimes they travel hurriedly, and while
their flights may be short, they must cover an appreciable distance
in the course of a day.
_How Birds Migrate_
=Speed of flight and speed of migration=
There is a widespread misconception concerning the speed at which
birds normally fly, and even regarding the speed they can attain when
occasion demands, as when closely pursued by an enemy. It is not
unusual to hear accounts of birds flying "a mile a minute." While
undoubtedly some birds can and do attain a speed even greater than
this, such cases are exceptional, and it is safe to say that even
when pressed, few can develop an air speed of 60 miles an hour. They
do, however, have two speeds, one being the normal rate for everyday
purposes and also for migration, and an accelerated speed for escape
or pursuit; this in some cases may be nearly double the normal rate
of movement. Nevertheless, it is doubtful if the effort required for
the high speeds could be long sustained, and certainly not for the
long-distance migratory journeys that are regularly made by most
birds. The theory that migrating birds attain high speeds received
encouragement from the German ornithologist Gätke (1895), who for
many years made observations on birds at the island of Heligoland.
He postulated that the blue-throat, a species of thrush smaller than
the American hermit thrush, would leave African winter quarters at
dusk and reach Heligoland at dawn, which would mean a sustained speed
of 200 miles an hour, and that the American golden plover flew from
the coast of Labrador to Brazil in 15 hours, or at the tremendous
speed of 250 miles an hour. Most ornithologists now consider these
conclusions to be unwarranted.
Sportsmen also often greatly overestimate the speed at which ducks
and geese fly and sometimes attempt to substantiate their estimates
by mathematical calculation, based upon the known velocity of a
charge of shot, the estimated distance and the estimated "lead" that
was necessary to hit the bird. If all three elements of the equation
were known with certainty, the speed of the bird could be determined
with a fair degree of accuracy. The majority of the ducks that are
reported as killed at 40, 50, or even 60 yards, however, actually
are shot at distances much less than estimated. To sight along a gun
barrel and estimate correctly the distance of a moving object against
the sky is so nearly impossible for the average gunner as to make
such calculations of little value.
During the past few years reliable data on the speed of birds have
accumulated slowly. It has been found that a common flying speed
of ducks and geese is between 40 and 50 miles an hour, and that it
is much less among the smaller birds. Herons, hawks, horned larks,
ravens, and shrikes, timed with the speedometer of an automobile,
have been found to fly 22 to 28 miles an hour, while some of the
flycatchers are such slow fliers that they attain only 10 to 17 miles
an hour. Even such fast-flying birds as the mourning dove rarely
exceed 35 miles an hour. All these birds can fly faster, but it is to
be remembered that at training camps during World War I, airplanes
having a maximum speed of about 80 miles an hour easily overtook
flocks of ducks that, it may be supposed, were making every effort
to escape. Aviators have claimed that at 65 miles an hour they can
overtake the fastest ducks, though cases are on record of ducks
passing airplanes that were making 55 miles an hour.
The greatest bird speeds that have been reliably recorded are of the
swifts and the duck hawk, or peregrine falcon. An observer in an
airplane in Mesopotamia reported that swifts easily circled his ship
when it was traveling at 68 miles an hour. To do this, the birds
certainly were flying at a speed as high as 100 miles an hour. Once
a hunting duck hawk, timed with a stop watch, was calculated to have
attained a speed between 165 and 180 miles an hour.
The speed of migration, however, is quite different from that
attained in forced flights for short distances. A sustained flight of
10 hours a day would carry herons, hawks, crows, and smaller birds
from 100 to 250 miles, while ducks and geese might travel as much as
400 to 500 miles in the same period. Measured as air-line distances,
these journeys are impressive and indicate that birds could cover the
ordinary migration route from the northern United States or even from
northern Canada to winter quarters in the West Indies or in Central
America or South America in a relatively short time. It is probable
that individual birds do make flights of the length indicated and
that barn swallows seen in May on Beata Island, off the southern
coast of the Dominican Republic, may have reached that point after a
nonstop flight of 350 miles across the Caribbean Sea from the coast
of Venezuela. Nevertheless, whether they continue such journeys day
after day is doubtful.
It seems more likely that migrations are performed in a leisurely
manner, and that after a flight of a few hours the birds pause to
feed and rest for one or several days, particularly if they find
themselves in congenial surroundings. Some indication of this is
found in the records of banded birds, particularly waterfowl.
Considering only the shortest intervals that have elapsed between
banding in the North and recovery in southern regions, it is found
that usually a month or more is taken to cover an air-line distance
of a thousand miles. For example, a black duck banded at Lake Scugog,
Ontario, was killed 12 days later at Vicksburg, Miss. If the bird was
taken shortly after its arrival, the record would indicate an average
daily flight of only 83 miles, a distance that could have been
covered in about 2 hours' flying time. Among the thousands of banding
records obtained in recent years, evidences of such rapid flight are
decidedly scarce, for with few exceptions all thousand-mile flights
have required 2 to 4 weeks or more. Among sportsmen, the blue-winged
teal is well known as a fast-flying duck and quite a few of these
banded on Canadian breeding grounds have covered 2,300 to 3,000 miles
in a 30-day period. Nevertheless, the majority of those that have
traveled to South America were not recovered in that region until
2 or 3 months after they were banded. Probably the fastest flight
over a long distance for one of these little ducks was one made by a
young male which traveled 3,800 miles from the delta of the Athabaska
River, in northern Alberta, Canada, to Maracaibo, Venezuela, in
exactly 1 month. This flight was at an average speed of 125 miles per
day. The greatest migration speed thus far recorded for any banded
bird is that of a lesser yellowlegs banded at North Eastham, Cape
Cod, Mass., on August 28, 1935, and killed 6 days later, 1,900 miles
away, at Lamentin, Martinique, French West Indies. This bird traveled
an average daily distance of more than 316 miles.
It seems certain that migratory journeys are performed at the normal
rate of flight, as this would best conserve the strength of the birds
and eliminate the fatigue that would result from effort required for
great speed. Migrating birds passing lightships and lighthouses, or
crossing the face of the moon, have been observed to fly without
hurry or evidence of straining to attain high speed.
The speed of migration also is demonstrated by the dates of arrival,
particularly during the spring movement. The Canada goose affords a
typical example of regular, but slow migration. Its advance northward
at this season is at the same rate as the advance of the season (fig.
4). In fact, the isotherm of 35° F. appears to be a governing factor
in the speed at which these geese move north, and over their entire
trip the vanguard follows closely the advance of this isotherm.
Few species perform such regular migrations, many waiting in their
winter homes until spring is well advanced and then moving rapidly
to their breeding grounds. Sometimes this advance is so rapid that
the later migrants actually catch up with species that for a month or
more may have been pressing slowly but steadily northward.
One of the best examples of rapid migration is found in the
gray-cheeked thrush. This bird winters in Colombia, Ecuador, Peru,
Venezuela, and British Guiana and does not start its northward
journey until many other species are well on their way. It does not
appear in the United States until the last of April--April 25 near
the mouth of the Mississippi, and April 30 in northern Florida (fig.
5). A month later, or by the last week in May, the bird is seen in
northwestern Alaska, the 4,000-mile trip from Louisiana having been
made at an average speed of about 130 miles a day.
[Illustration: _Figure 4._--Migration of the Canada goose. The
northward movement keeps pace with the advance of spring, in this
case the advance of the isotherm of 35° F. agreeing with that of the
birds.]
Another example of rapid migration is furnished by the yellow, or
summer, warbler. Coming from the Tropics, the birds reach New Orleans
about April 5, when the average temperature is 65° F. Traveling north
much faster than does the season, they reach their breeding grounds
in Manitoba the latter part of May, when the average temperature is
only 47°. Encountering progressively colder weather over their entire
route, they cross a strip of country in the 15 days from May 11 to 25
that spring temperatures take 35 days to cross. This "catching up"
with spring is habitual in species that winter south of the United
States and in most of the northern species that winter in the Gulf
States. To this rule there appear to be only six exceptions--the
Canada goose, the mallard, the pintail, the crow, the red-winged
blackbird, and the robin.
[Illustration: _Figure 5._--Isochronal migration lines of the
gray-cheeked thrush, an example of rapid migration. The distance
from Louisiana to Alaska is about 4,000 miles and is covered at
an average speed of about 130 miles a day. The last part of the
journey is covered at a speed that is several times what it is in the
Mississippi Valley.]
The blue goose presents a striking example of a late but very rapid
spring migration. Practically all members of the species winter in
the great coastal marshes of Louisiana, where 50,000 or more may
be seen grazing in the "pastures" or flying overhead in flocks of
various sizes. Their breeding grounds are chiefly on Baffin Island
and on Southampton Island in the northern part of Hudson Bay, in a
region where conditions of severe cold prevail except for a few weeks
each year. The birds seem to realize that even though the season in
their winter quarters is advancing rapidly, their nesting grounds
are still covered with a heavy blanket of ice and snow. Accordingly
they remain in the coastal marshes until the last of March or the
first of April, when the local birds are already busily engaged with
the duties of reproduction. The flight northward is rapid, almost
nonstop, so far as the United States is concerned, for although the
birds are sometimes recorded in large numbers in the Mississippi
Valley, including eastern South Dakota, and in southeastern Manitoba,
there are few records anywhere along the route of such great flocks
as are known to winter in Louisiana. When the birds arrive in the
James Bay region of Canada they apparently enjoy a prolonged period
of rest, as they are not noted in the vicinity of their breeding
grounds until the first of June. During the first 2 weeks of that
month they pour into the tundra country by the thousands, and each
pair immediately sets about the business of rearing a brood.
The robin has been mentioned as a slow migrant, and as a species it
takes 78 days to make the 3,000-mile trip from Iowa to Alaska, a
stretch of country that is crossed by advancing spring in 68 days.
In this case, however, it does not mean that individual robins are
necessarily slow, for probably the northward movement of the species
depends upon the continual advance of birds from the rear, the first
individuals arriving in a suitable locality remaining to nest, while
the northward movement of the species is continued by those still to
come.
Special interest attaches to the great variation in the speed
at which birds travel in different sections of the broad flyway
extending from the Gulf of Mexico to the Arctic Ocean, by way of
the Mississippi and Mackenzie Valleys. The blackpolled warbler
furnishes an excellent example (fig. 6). This species winters in
north-central South America and migrates in April across the West
Indies to Florida. From this point some individuals fly northwest to
the Mississippi Valley, north to Manitoba, northwest to the Mackenzie
River, and thence almost due west to western Alaska. In tracing
the long route of these birds it is found that a fairly uniform
average speed of 30 to 35 miles a day is maintained from the Gulf to
Minnesota. Then comes a spurt, for a week later the blackpolls have
reached the central part of the Mackenzie Valley and by the following
week they are observed in northwestern Alaska. During the latter
part of the journey, therefore, many individuals must average more
than 200 miles a day. They use 30 days in traveling from Florida to
southern Minnesota, a distance of about 1,000 miles, and scarcely
half that time to cover the remaining 2,500 miles to Alaska. It
should be noted that the increased speed is directly associated
with the change in direction, the north-and-south course in the
Mississippi Valley being accomplished slowly while the northwesterly
course across Canada is made at a much greater speed. Increased
speed across western Canada to Alaska is also shown by many other
birds. A study of all species traveling up the Mississippi Valley
indicates an average speed of about 23 miles a day. From southern
Minnesota to southern Manitoba 16 species maintain an average speed
of about 40 miles a day. From that point to Lake Athabaska, 12
species travel at an average speed of 72 miles a day; while 5 others
travel to Great Slave Lake at 116 miles a day; and another 5 species
cover 150 miles a day to reach Alaska. This change is in correlation
with a corresponding variation in the isothermal lines, which turn
northwestward west of the Great Lakes.
[Illustration: _Figure 6._--Migration of the blackpolled warbler. The
solid isochronal lines show the places at which these birds arrive at
the same time. As the birds move northward these lines become farther
apart, showing that the warblers move faster with the advance of
spring. From April 30 to May 10 the average speed is about 30 miles
a day, while from May 25 to May 30 it is increased to more than 200
miles.]
As has been previously indicated, the advance of spring in the
northern interior is much more rapid than in the Mississippi Valley
and on the Gulf coast. In other words, in the North spring comes with
a rush and during the height of the migration season in Saskatchewan
the temperature in the southern part of the Mackenzie Valley just
about equals that in the Lake Superior area, which is 700 miles
farther south. Such conditions, coupled with the diagonal course of
the birds across this region of fast-moving spring, exert a great
influence on migration and are the chief factors in the acceleration
of speed of travel.
Variations in speed of migration in different parts of the country
are illustrated also by the movements of the cliff swallow (fig.
3), which breeds from Mexico to Alaska and winters in Brazil and
Argentina. It would be expected in spring to appear in the United
States first in Florida and Texas then in the southern Rocky
Mountain region, and finally on the Pacific coast. As a matter of
fact, however, the earliest spring records come from north-central
California, where the bird usually is common before the first
arrivals are observed in Texas or Florida. The route taken, for many
years a migration problem, was solved when it was found that these
swallows went around the Gulf of Mexico rather than across it. The
isochronal lines on the map show the more rapid advance along the
Pacific coast. By March 20, when the vanguard has not quite reached
the lower Rio Grande in Texas, the species is already north of San
Francisco in California.
=Altitude at which birds travel=
At one time students of bird migration held firmly to the theory
that normal migration takes place at heights above 15,000 feet,
reasoning (somewhat uncertainly) that flying becomes easier as
altitude is gained. Since the development of the airplane, however,
and with it man's exploration of the upper regions of the air, it
has become common knowledge that rarified atmosphere adds greatly to
the difficulties of flight. This is due not only to the reduction in
oxygen (whether for gasoline engine or the lungs of a bird) but also
to the lack of buoyancy of the rarified air. Such birds as vultures,
pelicans, cranes, and some of the hawks feel this the least, since
compared with body weight the supporting surface of their wings is
very great, but for the smaller and shorter-winged birds lack of
buoyancy at high altitudes presents a difficult obstacle in flight.
Even when flying close to the earth, small birds have to keep their
wings in rapid motion.
Another postulate favoring the high-altitude flying theory was
that the wonderful vision of birds was their sole guidance during
migratory flights; and to keep landmarks in view the birds were
obliged to fly high, particularly when crossing wide areas of water.
This will be considered in greater detail under Orientation (p. 28),
so here it will be sufficient to say that birds rely only in part
upon vision to guide them on migration. Also, it is to be remembered
that there are definite physical limitations to the range of
visibility even under perfect atmospheric conditions. Chief of these
is the curvature of the earth's surface. Thus, if birds crossing the
Gulf of Mexico to Louisiana and Florida flew at a height of 5 miles,
they would still be unable to see a third of the way across. And yet
this trip is made twice each year by thousands of thrushes, warblers,
and others.
Actual knowledge of the altitude of migratory flight is scanty,
though estimates obtained by means of the telescope, and still more
accurate data resulting from altimeter observation from airplanes,
are slowly accumulating. It is, of course, obvious that some birds
that cross mountain ranges during migration must attain a great
altitude. Observers at an altitude of 14,000 feet in the Himalayas
have recorded storks and cranes flying so high that they could be
seen only through field glasses. Being beyond the range of unaided
vision they must have been at least 6,000 feet above the observers,
or at an actual altitude of 20,000 feet above sea level. Such cases,
however, are exceptional as aviators have reported that they rarely
meet birds above an altitude of 5,000 feet.
It is now known that migration in general is performed below a
height of 3,000 feet above the earth. Some proof of this statement
is available. Observations made from lighthouses and other points
of vantage indicate that migrants commonly travel at altitudes of a
very few feet to a few hundred feet above sea or land. Sandpipers,
sanderlings, and northern phalaropes, observed in migration on the
Pacific oceanic route, have been noted to fly so low that they
were visible only as they topped a wave. Observers stationed at
lighthouses and lightships off the English coast have similarly
recorded the passage of land birds, which sometimes flew just above
the surface of the water, and rarely above 200 feet. During the
World Wars broad areas in the air were under constant surveillance
and among the airplane pilots and observers many took more than a
casual interest in birds. Of the several hundred records resulting
from their observations only 36 were of birds flying above 5,000
feet, and only 7 above 8,500 feet. Cranes were once recorded at
an altitude of 15,000 feet, while the lapwing was the bird most
frequently seen at high levels, 8,500 feet being its greatest
recorded altitude.
These observations naturally relate only to daytime travelers, but
there is no reason to believe that nocturnal migration is performed
at higher altitudes. The fact that many birds are killed each year by
striking the lanterns at lighthouses, or other man-made obstructions,
does not, however, furnish conclusive proof that low altitudes are
generally used during nocturnal flight, for it should be recalled
that these accidents occur chiefly in foggy or unsettled weather, and
also that powerful lights have a great attraction for many species
of birds. The altitude at which birds travel is affected by other
weather conditions also. For example, flight at the higher elevations
is facilitated on clear, warm days by the currents of warm air that
ascend from broad areas.
=Orientation=
There probably is no single aspect of the entire subject of bird
migration that challenges our admiration so much as the unerring
certainty with which birds cover thousands of miles of land and
water to come to rest in exactly the same spot where they spent
the previous summer or winter. The records from birds marked with
numbered bands offer abundant proof that the same individuals of many
species will return again and again to their identical nesting sites.
These data show also that many individuals migrate in fall over
the same route, year after year, making the same stops and finally
arriving at the precise thicket that served them in previous winters.
The faculty that enables these birds to point their course accurately
over vast expanses of land and water may, for want of a better
term, be called a "sense of direction." Man recognizes this sense
in himself, though usually it is imperfect and frequently at fault.
Nevertheless the facility with which experienced hunters and woodsmen
locate tiny camps or other points in forested or mountainous country,
frequently cloaked by darkness or fog, with all recognizable
landmarks obliterated seems due to this faculty. Ability to travel
with precision over unmarked trails is not limited either to birds or
to man. It is likewise possessed by many other mammals as well as by
some insects and fishes, the well-known migrations of the salmon and
the eel being notable examples.
Ability to follow a more or less definite course to a definite goal
is evidently part of an inherited faculty. Both the path and the goal
must have been determined either when the habit originated or in the
course of its subsequent evolution. The theory is sometimes advanced
that the older and more experienced birds lead the way, showing the
route to their younger companions. This explanation may be acceptable
for some species, but not for those in which adults and the young
migrate at different times. The young cowbird that is reared by
foster parents flocks with others of its kind when grown and in many
cases can hardly be said to have adult guidance in migration. An
inherited migratory instinct with a definite sense of the goal to
be reached and the route to be followed must be attributed to these
birds.
It is well known that birds possess wonderful vision. If they also
have retentive memories subsequent trips over the route may well be
steered in part by recognizable landmarks. The arguments against the
theory of vision and memory are chiefly that much migration takes
place by night and that great stretches of the open sea are crossed
without hesitation. Nevertheless, the nights are rarely so dark that
all terrestrial objects are totally obscured, and such features as
coastlines and rivers are just those that are most likely to be
seen in the faintest light, particularly by the acute vision of the
bird and from its aerial points of observation. But some birds fly
unerringly through the densest fog. Members of the Biological Survey,
proceeding by steamer from the island of Unalaska to Bogoslof Island
in Bering Sea, through a fog that was so heavy as to make invisible
every object beyond a hundred yards, recorded the fact that flocks of
murres, returning to Bogoslof, after quests for food, broke through
the wall of fog astern, flew by the vessel, and disappeared into the
mists ahead. The ship was heading direct for the island by the use of
compass and chart, but its course was no more sure than that of the
birds.
Some investigators have asserted that the sense of direction has its
seat in the ears or nasal passages and thus that the bird is enabled
to identify air currents and other phenomena. It has been found that
disturbance of the columella or the semicircular canals of the inner
ear will destroy the homing instinct of the racing pigeon, but
experiments in the form of delicate operations, or closing the ears
with wax, prove such a serious shock to the sensitive nervous system
of the bird that they cannot be considered as affording conclusive
evidence. Several years ago careful studies were made of the homing
instinct of the sooty and noddy terns, tropical species that in the
Atlantic region reach their most northern breeding point on the Dry
Tortugas Islands, off the southwest coast of Florida. They are not
known to wander regularly any appreciable distance farther north.
It was found that some were able to return to their nests on the
Tortugas after they had been taken on board ship, confined in cages
below decks, and carried northward to distances varying from 400 to
800 miles before being released. Landmarks of all kinds were entirely
lacking, and the birds certainly were liberated in a region in which
they had had no previous experience.
Possibly the "homing instinct" as shown by these terns, by the
man-o'-war birds that are trained and used as message carriers in the
Tuamotu, Gilbert, and Marshall Islands, and by the homing pigeon, is
not identical with the sense of perceptive orientation that figures
in the flights of migratory birds. Nevertheless, it seems closely
akin and is probably caused by the same impulses, whatever they
may be and however they may be received. It should be remembered,
however, that while homing may involve flight from a point that
the bird has never before visited, the flight is always to a known
point--that is, the bird's nest--while, on the other hand, the first
migratory flight is always from the region of the bird's birth to a
region it has never before visited. The spring migration might, of
course, be more nearly considered as true "homing."
Some students have leaned strongly toward the possible existence
of a "magnetic sense" as being the important factor in the power
of geographical orientation. The theory that migratory birds might
be responsive to the magnetic field of the earth was conceived as
early as 1855, when some experimental work was done in Russia, and
nearly 60 years later in France. Recently investigations in this
field have been conducted by Yeagley (1947) and by Gordon (1948)
with diametrically opposite results. The idea carries with it the
implication that contained in the bird's body is an organ that is
sensitive to the effect of its motion through the vertical component
of the magnetic field and to other related factors. In the tests by
Dr. Yeagley, 20 young homing pigeons were given training flights to
their home loft from distances up to 100 miles. Permanent magnets
were then affixed to the under side of the manus part of the wings
of half of the birds while copper plates of equivalent weight were
attached to the wings of the other half. All birds were released
singly at an air-line distance of about 65 miles from the loft. The
results were most suggestive, as only two of the birds carrying
magnets returned to the loft, whereas eight of the controls returned.
With certain minor modifications, this experiment was repeated by
Gordon. In this case 60 pigeons were used and releases were made from
points up to 58 miles, where the direction of flight was such that
the birds had to navigate across the gradient of the magnetic field.
Every bird returned to its loft on the day of release regardless of
whether it carried magnets or unmagnetized bars of the same weight.
Attempts to demonstrate the effect of radio waves on the navigational
ability of birds also have produced contradictory results. In some of
these tests, homing pigeons released near broadcasting stations have
appeared to be hopelessly confused, whereas in others, apparently
conducted in the same manner, no effects could be discerned. It is
obvious that before the electromagnetic theory can be accepted or
rejected, much additional experimental work is necessary.
In concluding this discussion of orientation it is pertinent to
point out that the migratory instinct appears to be more or less
transitory, that it is not persistent over an extended period.
Migratory birds may be arrested en route, either by natural
conditions, such as unusual food supplies, or forcibly by the act of
man, and detained until the end or nearly the end of the migratory
season, and then may not attempt to finish the journey, apparently
having lost the migratory impulse. In the fall and early winter of
1929, abundant food and an open season caused an unusual number of
mallard ducks to arrest their migration and remain in western Montana
and northern Idaho. Later, however, a heavy snowfall with subzero
temperatures suddenly cut off the food supply, with the result that
great numbers of the birds starved to death, when a flight of a few
hours would have carried them to a region of open water and abundant
food.
=Segregation during migration=
During the height of the northward movement in spring the woods
and thickets may be suddenly filled with several species of wood
warblers, thrushes, sparrows, flycatchers, and others, which
it is natural to conclude have traveled together and arrived
simultaneously. Probably they did, but such combined migration is by
no means the rule for all species.
As a group the wood warblers (_Compsothlypidae_) probably travel more
in mixed companies than do any other single family of North American
birds. The flocks are likely to be made up of several species in
spring and fall with both adults and young. Sometimes swallows,
sparrows, blackbirds, and some of the shore birds also migrate in
mixed flocks. In fall, great flocks of blackbirds frequently sweep
south across the Plains States, and occasionally one flock will
contain bronzed grackles, red-winged blackbirds, yellow-headed
blackbirds, and Brewer's blackbirds.
On the other hand many species keep strictly to themselves. It would
be difficult for any other kind of bird to keep in company with
one of such rapid movements as the chimney swift, which is rarely
found associated with any other species at any season. Nighthawks
or bullbats also fly in separate companies, as do usually crows,
waxwings, crossbills, bobolinks, and kingbirds. Occasionally, a flock
of ducks will be observed to contain several species, but generally
when they are actually on migration the individuals of each species
separate and travel with others of their own kind. The flocks of
blue geese, previously mentioned in connection with speed of flight
(p. 22), frequently have with them a few of the closely related snow
geese, particularly in the eastern part of their winter range. The
portion here is usually about 10 to 1, but farther west the numbers
of snow geese increase until they outnumber their blue relatives.
The adults of most perching birds drive the young away when they are
grown, probably to be relieved of the necessity of providing for
them, and also in order that the parents may have opportunity to rest
and renew their plumage before starting for winter quarters. The
young birds are therefore likely to drift together and, having no
further responsibility, may start south ahead of their parents. In
contrast with this indifference on the part of the adults of perching
birds, Canada geese and some others remain in family groups, the
parent birds undergoing the wing molt that renders them flightless
during the period of growth of their young, so that old and young
acquire their full plumage at the same time and are able to start
south together. The large flocks, therefore, are composed of many
families that band together, and when they separate into =V=-shaped
units it is probably correct to assume that it is an old bird that
leads the group. Where there is segregation of the sexes, the young
birds usually accompany their mothers, as is the case with some of
the ducks. After the females start to incubate their eggs, the males
of most species of ducks flock by themselves and remain together
until fall.
The males and females of some species may migrate either
simultaneously or separately. In the latter case it is usually the
males that arrive first, sometimes great flocks of male birds, as in
the red-winged blackbird, reaching a locality several days before any
of the females. This is particularly the rule in spring: The first
robins are usually found to be males, as are also the first song
sparrows, rose-breasted grosbeaks, and scarlet tanagers. This early
arrival of the males has been explained on the theory of territorial
possession, under which the male selects the area where it elects to
breed, each individual attempting to protect a definite territory
from trespass by other males of his own kind, at the same time
singing or otherwise announcing his presence and inviting the later
arriving female to examine the territory that he has selected for
nesting. The long-billed marsh wren is a noteworthy example, and the
males of this species may enthusiastically build several dummy nests
before the females arrive.
In a few species the males and females apparently arrive at the
breeding grounds together and proceed at once to nest building. In
fact among the shore birds, ducks, and geese, courtship and mating
may take place in whole or in part while the birds are in the South
or on their way north, so that when they arrive at the northern
nesting grounds they are paired and ready to proceed at once with
the raising of their families. Mallards and black ducks may be
observed in pairs as early as January, the female leading and the
male following when they take flight. Naturally these mated pairs
migrate north in company, and it was largely to protect such species
that duck shooting in spring was abolished by Federal law a number of
years ago.
Many shore birds nest well within the Arctic Circle, and it is the
opinion of ornithologists that most of these birds share, at least
in part, the habits of the phalaropes, a family in which the male
assumes the entire care of the eggs and young. If this be true, it
explains why in southern latitudes so many of the earliest fall
arrivals are females that may have deserted the breeding grounds
after the eggs were laid.
Migratory flights are frequently accomplished in close flock
formation, as with the shore birds, blackbirds, and waxwings, and
especially some of the sparrows--the snow buntings, longspurs,
juncos, and tree sparrows. Other species, however, though they travel
in flocks, maintain a very loose formation; examples are the turkey
vultures, the hawks, swifts, blue jays, swallows, warblers, and
bluebirds. Still others, the grebes, great horned owls, winter wrens,
shrikes, and belted kingfishers for example, ordinarily travel alone
and when several are found in close proximity it is an indication
that they have been drawn together by unusual conditions, such as
abundant food.
_Where Birds Migrate_
Definite evidence shows that both the length and the duration of the
migratory journey vary greatly. The bobwhite and the western quails,
the cardinal, the Carolina wren, and probably some of the titmice and
woodpeckers, which are apparently almost or quite nonmigratory, may
round out their full period of existence without at any time going
more than lo miles from the nest where they were hatched.
=Short and undetermined migrations=
Song sparrows, meadow larks, blue jays, and some other species make
such short migrations that the movement is difficult to detect, as
individuals may be found in one area throughout the year. Thus, at
the southern part of the range there is merely a concentration in
winter, the summer individuals being entirely sedentary. Speculation
is useless on the distances of individual migration without definite
evidence concerning the precise winter quarters of birds that summer
in a particular part of the breeding range of the species, but from
the records of banded birds important evidence is becoming available.
Eventually it may be possible to say definitely just how far the song
sparrows that nest in northern New England and the Maritime Provinces
of Canada travel to their winter quarters, and whether the blue jays
of New York and the upper Mississippi Valley remain throughout the
winter in their breeding areas, or move farther south and relinquish
their places to individuals from southern Canada.
An illustration of what is now known on this subject is found in the
case of the robin. This bird occurs in the Middle Atlantic States
throughout the year, in Canada only in summer, and along the Gulf
coast only as a winter resident. On the Atlantic coast its movements
are readily ascertained, since, for example, in the section about
Washington, D. C., the breeding robin is the southern variety
(_Turdus migratorius archrusterus_) which is found there from the
first of April to the last of October, when its place is taken
(in smaller numbers) by the northern robin (_Turdus migratorius
migratorius_), which arrives about the middle of October and remains
until the following April. It is probable that a similar interchange
of individual robins occurs throughout a large part of the balance of
its range, the hardy birds from the north being the winter tenants in
the abandoned summer homes of the southern birds.
The red-winged blackbirds that nest in northern Texas are almost
sedentary, but in winter they are joined by representatives of other
subspecies that nest as far north as the Mackenzie Valley.
=Variable migrations within species=
The difference in characters between subspecies has been used by
students of migration to discover other interesting facts concerning
variations of the migratory flight between closely related birds
that breed in different latitudes. The familiar eastern fox sparrow
(_Passerella iliaca iliaca_) breeds from northwestern Alaska to
Labrador, and in winter is found concentrated in the southeastern
part of the United States. It thus travels a long distance each year.
On the west coast of the continent, however, six subspecies of this
bird breed in rather sharply delimited ranges, extending from the
region of Puget Sound and Vancouver Island to Unimak Island, at the
end of the Alaskan Peninsula. One of these, known as the sooty fox
sparrow (_P. i. fuliginosa_) breeds in the Puget Sound area and makes
practically no migration at all, while the other races, nesting on
the coast of British Columbia and Alaska, are found in winter chiefly
in California. The races that breed farthest north are in winter
found farthest south, illustrating a tendency for those birds that
are forced to migrate to pass over those so favorably located that
they have no need to leave their breeding areas, while the northern
birds settle for the winter in the unoccupied areas farther south
(fig, 7).
Another example of the same kind is the Maryland yellowthroat of
the Atlantic coast. Birds occupying the most southern part of the
general range are almost nonmigratory, residing throughout the year
in Florida, while those breeding as far north as Newfoundland go to
the West Indies for the winter, thus passing directly over the home
of their southern relatives.
[Illustration: _Figure 7._--Migration of Pacific-coast forms of the
fox sparrow. The breeding ranges of the different races are encircled
by solid lines, while the winter ranges are dotted. The numbers
indicate the areas used by the different subspecies, as follows: 1.
Shumagin fox sparrow; 2. Kodiak fox sparrow; 3. Valdez fox sparrow;
4. Yakutat fox sparrow; 5. Townsend fox sparrow; 6. Sooty fox
sparrow (After Swarth, courtesy of the Museum of Vertebrate Zoology,
University of California).]
The palm warbler (_Dendroica palmarum_) which breeds from Nova
Scotia and Maine west and northwest to southern Mackenzie, has been
separated into two subspecies. Those breeding in the interior of
Canada (_D. p. palmarum_) make a 3,000-mile journey from Great Slave
Lake to Cuba, passing through the Gulf States early in October. After
the bulk have passed, the palm warblers from the Northeastern States
and Provinces (_D. p. hypochrysea_) drift slowly into the Gulf Coast
region, where they remain for the winter. Their migratory journey is
about half as long as that of the northwestern subspecies.
There is no invariable law governing the distance of migration,
although in general it is found that where a species has an extensive
range, the subspecies that breed farthest north go farthest south to
spend the winter.
=Fall flights not far south of breeding ranges=
Some other species that have extensive summer ranges, for instance
the pine warbler, rock wren, field sparrow, loggerhead shrike, and
black-headed grosbeak, are found to concentrate during the winter
season in the southern part of the breeding range, or to occupy
additional territory that is only a short distance farther south.
The entire species may thus be confined within a restricted area for
the period of winter, and then, with the return of warmer weather,
spreads out to reoccupy the full range.
There are many species, including the tree sparrow, slate-colored
junco, and Lapland longspur, that nest in Canada and winter in the
United States; while others, including the vesper sparrow, chipping
sparrow, grackles, red-winged blackbirds, bluebirds, the woodcock,
and several species of ducks, nest in the northern United States and
move south for the winter to areas along the Gulf of Mexico. This
list includes the more hardy species, some individuals of which may
linger in protected places well within the reach of severe cold, as,
for example, Wilson's snipe or jacksnipe, which frequently is found
during subzero weather in parts of the Rocky Mountain region where
warm springs assure a food supply. More than 100 of our summer birds
leave the United States entirely and spend the winter in the West
Indies, or in Central America or South America. For example, the
Cape May warbler, which breeds from northern New England, northern
Michigan, and northern Minnesota, north to New Brunswick, Nova
Scotia, and nearly to Great Slave Lake, is concentrated in winter
chiefly in the West Indies, its metropolis at this season being the
island of Hispaniola.
=Long-distance migrations=
Some of the common summer residents are not content with a trip to
northern South America, but push on across the Equator and finally
come to rest for the winter in the pampas of Argentina, or even
in Patagonia. Thus some species that are more or less associated
with each other in summer, as nighthawks, barn swallows, cliff
swallows, and some of the thrushes, may also occupy the same general
winter quarters in Brazil. Some individual nighthawks and barn
swallows travel still farther, and of all North American land birds
these species probably have the longest migration route, as they
occur north in summer to Yukon and Alaska, and south in winter to
Argentina, 7,000 miles away. Such seasonal flights are exceeded in
length, however, by the journeys of several species of water birds,
chiefly members of the suborder of shore birds. In this group there
are 19 species that breed north of the Arctic Circle and winter in
South America, 6 of them going as far south as Patagonia, and thus
having a migration route more than 8,000 miles in length.
The arctic tern is the champion "globe trotter" and long-distance
flier (fig. 8). Its name "arctic" is well earned, as its breeding
range is circumpolar and it nests as far north as it can find a
suitable place. The first nest to be found in this region was only
7½ degrees from the North Pole, and it contained a downy chick
surrounded by a wall of newly fallen snow that had been scooped
out by the parent. In North America the arctic tern breeds south
in the interior to Great Slave Lake, and on the Atlantic coast to
Massachusetts. After the young are grown the arctic terns disappear
from their North American breeding grounds, and a few months later
they may be found in the Antarctic region, 11,000 miles away. Until
very recently the route followed by these hardy fliers was a complete
mystery, for although a few scattered individuals have been noted
south as far as Long Island, the species is otherwise practically
unknown along the Atlantic coasts of North America and South America.
It is, however, known as a migrant on the west coast of Europe and
Africa. By means of numbered bands the picture is now developing of
what is apparently not only the longest but also one of the most
remarkable of all migratory journeys.
[Illustration: _Figure 8._--Distribution and migration of the arctic
terns of eastern North America. The route indicated for this bird is
unique, as no other species is known to breed abundantly in North
America and to cross the Atlantic Ocean to and from the Old World.
The extreme summer and winter homes are 11,000 miles apart, and as
the route taken is circuitous, these terns probably fly at least
25,000 miles each year.]
Judging by the evidence at present available it seems likely that
the arctic terns of eastern North America originally found their way
here from the Old World, probably by way of Iceland and Greenland.
Consequently when the time comes for them to migrate to winter
quarters they do not go directly south as do the common and Forster's
terns, but instead they fly back eastward along their ancestral route
across the Atlantic to the shores of Europe and then go south along
the African coast to their winter home. Those that breed in the
northwestern part of the continent, as in Alaska, probably migrate
chiefly down the western coast, as the species is not infrequently
reported on the coast of California and also on the western coast of
South America.
The evidence yielded by banding consists of only six definite cases,
but their interpretation permits but one conclusion. All were banded
either as downy chicks or as nonflying immature birds. The details
of their banding and recovery are of sufficient interest to justify
citing in detail. The first was banded on July 3, 1913, at Eastern
Egg Rock, Maine,[2] and in August 1917 was found dead in the Niger
River delta, West Africa. The second was banded at the Red Islands,
Turnevik Bay, Labrador, on July 22, 1927, and was recovered near La
Rochelle, France, on October 1, 1927. The third, also banded on the
Red Islands, on July 23, 1928, was retaken at Margate, near Port
Shepstone, Natal, South Africa, on November 14, 1928. The fourth,
banded at Machias Seal Island, New Brunswick, on July 20, 1935, was
captured near St. Nazaire, France, October 8, 1935. The fifth and
sixth were banded at Machias Seal Island also; the fifth, banded
July 5, 1947, was found on November 10, 1948, at Kingfisher Creek,
Sedgefield, near Wilderness, Eastern Cape Province, South Africa,
while the sixth, banded on July 18, 1948, was picked up dead during
the latter part of September 1948 on the hills near Kyle Strome,
Sutherland, Scotland. All that remained of the bird that provides
the last-named case was a mutilated foot and it appeared that it had
been the victim of some predator. It should be pointed out that the
flights indicated in the third and fifth cases detailed above, are
the longest known for any birds. Both are between 8,000 and 9,000
miles, which in the case of No. 3 was accomplished in less than 3
months.
[2] Recorded at the time of banding as a common tern, a natural
error, as the downy young of common and arctic terns look almost
exactly alike.
Probably no other animal in the world enjoys as many hours of
daylight as does the arctic tern, since for these birds the sun never
sets during the nesting season in the northern part of the range,
while during their sojourn in the south, daylight is continuous.
During several months of the year they have 24 hours of daylight and
during the other months considerably more daylight than darkness.
_Routes of Migration_
While it is beyond question that certain general directions of flight
are constantly followed by migratory birds, it is well to remember
that the term "migration route" is to some extent a theoretical
concept concerned entirely with the lines of general advance or
retreat of a species, rather than the exact course followed by
individual birds. Even the records of banded birds usually show
no more than the place of banding and recovery, and one must
have recourse to intermediate records and to reasoning based on
probabilities to fill in details of the route actually traversed
between the two points.
There is also infinite variety in the routes covered during migration
by different species. In fact, the choice of migration highways is
so wide that it seems as if the routes of no two species coincide.
Differences in distance traveled, time of starting, speed of flight,
geographical position, latitudes of breeding and of wintering
grounds, and in other factors, all contribute to this great variation
of migration routes. Nevertheless, there are certain factors that
serve to guide the avian travelers along more or less definite lines,
and it is possible to define general lines of migration for the
majority of species.
It has been frequently observed that migrating birds have a tendency
to follow major topographic lines on the earth's surface when their
trend is in the general direction of the birds' journey. Bird
migration is generally thought of as a north-and-south movement, with
the lanes of heavier concentration following the coasts, mountain
ranges, and principal river valleys. To a considerable extent this
is the case, particularly in North America, where the coast lines,
mountain chains, and larger rivers in general run north and south.
In cases where the migration is a long one, however, the notion must
be abandoned that the birds' flight is always restricted to narrow
routes that follow river valleys and the like, as many species seem
to disregard utterly such apparently good natural highways. For
example, the Arkansas River has a general east-and-west course for a
great part of its length, and while it does constitute a route for
many perching birds en route from the Mississippi Valley to the Rocky
Mountain region, some of the hawks and many ducks and shore birds
pay the valley scant attention. They may arrest the autumn journey
to feed among the cottonwoods or along sand bars, but when ready to
resume their flight they leave the river and fly directly south over
the more or less arid region that lies between the Arkansas and the
Rio Grande.
=Wide and narrow migration lanes=
When birds start their southward migration the movement necessarily
involves the full width of the breeding range. Later there is a
convergence of the lines of flight taken by individual birds, owing
to the conformation of the land mass, and as the species proceeds
southward the width of the occupied region becomes less and less. An
example of this is provided by the common kingbird, which breeds from
Newfoundland to British Columbia, a summer range 2,800 miles wide. On
migration, however, its paths converge until in the southern part of
the United States the occupied area extends from Florida to the mouth
of the Rio Grande, a distance of only 900 miles, and still farther
south the migration path is further restricted. In the latitude of
Yucatan it is not more than 400 miles wide, and it is probable that
the great bulk of the species moves in a belt that is less than half
that width.
A migration route, therefore, may be anything from a narrow path
that adheres closely to some definite geographical feature, such as
a river valley or a coast line, to a broad boulevard that leads in
the desired direction and which follows only the general trend of the
land mass. Also it is to be remembered that whatever main routes are
described, there remains a multitude of tributary and separate minor
routes. In fact, with the entire continent of North America crossed
by migratory birds, the different groups or species frequently follow
lines that may repeatedly intersect those taken by others of their
own kind or by other species. The arterial routes, therefore, must
be considered merely as indicating paths of migration on which the
tendency to concentrate is particularly noticeable.
In considering the width of migration lanes it will be obvious that
certain species, as the knot and the purple sandpiper, which are
normally found only along the coasts, must have extremely narrow
routes of travel. They are limited on one side by the broad waters of
the ocean, and on the other by land and fresh water, both of which
are unsuited to furnish the food that is desired and necessary to the
well-being of these species.
[Illustration: _Figure 9._--Breeding and wintering ranges and
migration of Harris's sparrow, an example of a narrow migration
route through the interior of the country. The heavy broken lines
enclose the region traversed by the majority of these finches; the
light broken line encloses the country where they occur with more or
less regularity; while the spots indicate records of accidental or
sporadic occurrence.]
Among land birds that have a definite migration, the Ipswich sparrow
has what is probably the most restricted migration range of any
species. It is known to breed only on Sable Island, Nova Scotia,
and it winters along the Atlantic coast south to Georgia. Living
constantly within sound of the surf, it is rarely more than a quarter
of a mile from the outer beach, and is entirely at home among the
sand dunes and their sparse covering of coarse grass.
[Illustration: _Figure 10._--Distribution and migration of the
scarlet tanager. During the breeding season individual scarlet
tanagers may be 1,900 miles apart in an east-and-west line across the
breeding range. In migration, however, the lines converge until in
southern Central America they are not more than 100 miles apart. For
migration paths of other widths see figures 9, 11, and 12.]
Harris's sparrow supplies an interesting example of a narrow
migration route in the interior of the country (fig. 9.) This fine,
large finch is known to breed only in the region from Churchill, on
the west shore of Hudson Bay, northwest to the shores of Great Bear
Lake. Very few actual breeding records of the species are available,
but these are sufficient to indicate that the breeding range is in
the strip of country characterized by more or less stunted timber
just south of the limit of trees. When it begins its fall migration,
this species necessarily covers the full width of its breeding area.
Then it proceeds almost directly south, or slightly southeasterly,
the area covered by the majority of the birds becoming gradually
constricted, so that by the time it reaches the United States it is
most numerous in a belt about 500 miles wide, extending across North
Dakota to central Minnesota. Harris's sparrows are noted on migration
with fair regularity east to the western shore of Lake Michigan, and
west to the foothills of the Rocky Mountains, but the great bulk of
the species moves north and south through a relatively narrow path in
the central part of the continent. Present knowledge suggests that
the reason for this narrow migration range is the close association
that Harris's sparrow maintains with a certain type of habitat'
including brushy places, thickets, edges of groves, and weed patches.
While these environmental conditions are found in other parts of
the country, the region crossed by this sparrow presents almost a
continuous succession of habitat of this type. Its winter range
extends from southeastern Nebraska and northwestern Missouri, across
eastern Kansas and Oklahoma and through a narrow section of central
Texas, at places hardly more than 150 miles wide.
The scarlet tanager presents another extreme case of narrowness of
migration route (fig. 10), its breeding range extending in greatest
width from New Brunswick to Saskatchewan, a distance of about 1,900
miles. As the birds move southward in fall their path of migration
becomes more and more constricted, until at the time they leave the
United States all are included in the 600-mile belt from eastern
Texas to the Florida peninsula. Continuing to converge through
Honduras and Costa Rica, the boundaries there are not more than 100
miles apart. The species winters in northwestern South America, where
it spreads out over most of Colombia, Ecuador, and Peru.
The rose-breasted grosbeak also leaves the United States through
the 600-mile stretch from eastern Texas to Apalachicola Bay, but
thereafter the lines do not further converge, as this grosbeak enters
the northern part of its winter quarters in Central America and South
America through a door of about the same width (fig. 11).
Although the cases cited represent extremes of convergence, a
narrowing of the migratory path is the rule to a greater or less
degree for the majority of North American birds. The shape of the
continent tends to effect this, and so the width of the migration
route in the latitude of the Gulf of Mexico is usually much less than
in the breeding territory.
The redstart represents a notable case of a wide migration route,
although even in the southern United States this is much narrower
than the breeding range (fig. 12). These birds, however, cross all
parts of the Gulf of Mexico and pass from Florida to Cuba and Haiti
by way of the Bahamas, so that here their route has a width of about
2,500 miles.
[Illustration: _Figure 11._--Distribution and migration of the
rose-breasted grosbeak. Though the width of the breeding range is
about 2,500 miles, the migratory lines converge until the boundaries
are only about 700 miles apart when the birds leave the United
States. For migration paths of other widths see figures 9, 10, and
12.]
=The flyways=
In 1935, as a result of studies of banding data, the author
discovered the existence of the four great flyway systems. This
discovery, based upon analyses of the several thousand records of
the recovery of migratory waterfowl then available, was announced by
the Biological Survey (Lincoln, 1935c) and, beginning in 1948, it
has served as the basis for administrative action by the Fish and
Wildlife Service in the annual hunting regulations.
[Illustration: _Figure 12._--Distribution and migration of the
redstart. An example of a wide migration route, since birds of this
species cross all parts of the Gulf of Mexico, or may travel from
Florida to Cuba and through the Bahamas. Their route thus has an
east-and-west width of more than 2,000 miles. For migration paths of
greater or less extent see figures 9, 10, and 11.]
Although this study was confined to this one family of birds there
is a growing mass of evidence in support of the belief that all
populations of migratory birds adhere with more or less fidelity to
their respective flyways. The terms "flyway" and "migration route"
have in the past been used more or less as synonyms but the modern
concept of a flyway is that it is a vast geographic region with
extensive breeding grounds and wintering grounds connected with each
other by a more or less complicated system of migration routes. Each
flyway has its own populations of birds, even of those species that
may have a continental distribution. The breeding grounds of one or
more flyways may (and usually do) overlap broadly, so that during the
nesting season extensive areas may be occupied by birds of the same
species but which belong to different flyways.
The maps (figs. 13, 14, 15, and 16) show the flyways as they are now
understood. It should be pointed out, however, that in the other maps
used in this bulletin, the entire range of a species is shown without
any attempt to distinguish by flyways the different populations. As
banding data accumulate for the nongame species, this distinction
will ultimately be possible, but for the time being, consideration of
their migrations must be chiefly by routes.
The following discussion of the principal routes of North American
birds relates chiefly to the fall migration, for, except as otherwise
noted, the spring flight generally retraces the same course. The
routes indicated on the map (fig. 17) must not be considered as
representing paths with clearly defined borders, but rather as
convenient subdivisions of the four great flyways that, as indicated
above, cover practically the entire width of the North American
Continent and extend from the Arctic coast to South America.
[Illustration: _Figure 13._--The Atlantic flyway.]
=Atlantic oceanic route=
By reference to figure 17 it will be noted that route No. 1 is almost
entirely oceanic, passing directly over the Atlantic Ocean from
Labrador and Nova Scotia to the Lesser Antilles, and then through
this group of small islands to the mainland of South America. This
is not a popular route and its chief claim to fame is that it is the
fall route used by most of the adult eastern golden plovers, and
probably by some other shore birds. Since it lies entirely over the
sea, this route is definitely known only at its terminals and from
occasional observations made on Bermuda and other islands in its
course. Some of the shore birds that breed on the Arctic tundra of
Mackenzie and Alaska fly southeastward across Canada to the Atlantic
coast and finally follow this oceanic route to the mainland of South
America. The golden plover may accomplish the whole 2,400 miles
without pause or rest, in fair weather the flocks passing Bermuda and
sometimes even the islands of the Antilles without stopping. Although
most birds make their migratory flights either by day or by night,
the golden plover in this remarkable journey flies both day and
night. As it swims lightly and easily it may make a few short stops
along the way, and it has been seen actually resting on the ocean.
Other shore birds have been observed busily feeding in the great area
of ocean known as the Sargasso Sea, where thousands of square miles
of floating seaweed teem with marine life.
[Illustration: _Figure 14._--The Mississippi flyway.]
[Illustration: _Figure 15._--The Central flyway.]
[Illustration: _Figure 16._--The Pacific flyway.]
The annual flight of the adult eastern golden plover is so wonderful
that it may be given in some detail, particularly since it is one of
the exceptions to the general rule that spring and fall movements are
over the same routes (fig. 18). After reaching the South American
coast the birds make a short stop and then continue overland to the
pampas of Argentina, where they remain from September to March.
Leaving their winter quarters, they cross northwestern South America
and the Gulf of Mexico, reaching the North American mainland on the
coasts of Texas and Louisiana. Thence they proceed slowly up the
Mississippi Valley, and by the early part of June are again on their
breeding grounds, having performed a round-trip journey in the form
of an enormous ellipse with the minor axis about 2,000 miles and
the major axis 8,000 miles, reaching from the Arctic tundra to the
pampas of Argentina. The older birds are probably accompanied by
some of the young, perhaps those from early nestings, but most of
the immature birds leave their natal grounds late in summer and move
southward through the interior of the country, returning in spring
over essentially the same course. The elliptical route is therefore
used chiefly by fully adult birds.
[Illustration: _Figure 17._--Principal migration routes used by birds
in passing from North America to winter quarters in the West Indies,
Central America, and South America. Route No. 4 is the one used most
extensively; only a few species make the 2,400-mile flight from Nova
Scotia to South America.]
[Illustration: _Figure 18._--Distribution and migration of the golden
plover. Adults of the eastern form migrate across northeastern
Canada and then by a nonstop flight reach South America. In spring
they return by way of the Mississippi Valley. Their entire route is
therefore in the form of a great ellipse with a major axis of 8,000
miles and a minor axis of about 2,000 miles. The Pacific golden
plover, which breeds in Alaska, apparently makes a nonstop flight
across the ocean to Hawaii, the Marquesas Islands, and the Low
Archipelago, returning in spring over the same route.]
=Atlantic coast route and tributaries=
The Atlantic coast is a regular avenue of travel, and along it are
many famous points for observing both land and water birds. About 50
different kinds of land birds that breed in New England follow the
coast southward to Florida and travel thence by island and mainland
to South America (fig. 17, route 2). As will be seen from the map, a
seemingly natural and convenient highway extends through the Bahamas,
Cuba, Hispaniola, Puerto Rico, and the Lesser Antilles to the South
American coast. Resting places are afforded at convenient intervals,
and at no time need the aerial travelers be out of sight of land. It
is not, however, the favored highway, and only about 25 species of
birds go beyond Cuba to Puerto Rico along this route to their winter
quarters, while only 6 species are known to reach South America by
way of the Lesser Antilles. The obvious draw-back is lack of adequate
food. The total area of all the West Indies east of Puerto Rico is
less than that of Rhode Island, so that if only a small part of
the birds of the eastern United States were to travel this way, it
is doubtful whether even the luxuriant flora and fauna of tropical
habitats would provide food sufficient for their needs. Nevertheless,
many thousands of coots, widgeons, pintails, blue-winged teal, and
other waterfowl and shorebirds regularly spend the winter season
in the coastal marshes and the inland lakes and ponds of Cuba,
Hispaniola, and Puerto Rico.
The map (fig. 17) also will show that route No. 3 presents a direct
line of travel for Atlantic coast migrants en route to South America,
although it involves much longer flights. It is used almost entirely
by land birds. After taking off from the coast of Florida there are
only two intermediate land masses where the migrants may pause for
rest and food. Nevertheless, tens of thousands of birds of some 60
species cross the 150 miles from Florida to Cuba where about half
this number elect to remain for the winter months. The others do not
hesitate to fly the 90 miles between Cuba and Jamaica, but from that
point to the South American coast there is a stretch of islandless
ocean fully 500 miles across. Scarcely a third of the North American
migrants leave the forested mountains of Jamaica to risk the perils
of this ocean trip. Chief among these is the bobolink, which so far
outnumbers all other birds using this route that it may be well
called the "bobolink route" (fig. 19). As traveling companions
along this route, the bobolink may meet a vireo, a kingbird, and a
nighthawk from Florida; the chuck-wills-widow of the Southeastern
States; the black-billed and the yellow-billed cuckoos from New
England; the gray-cheeked thrush from Quebec; bank swallows from
Labrador; and the blackpolled warbler from Alaska. Sometimes this
scattered assemblage will be joined by a tanager or a wood thrush
but the "bobolink route" is not popular with the greater number of
migrants, and although many individuals traverse it, they are only a
small fraction of the multitudes of North American birds that spend
the winter in South America.
[Illustration: _Figure 19._--Distribution and migration of the
bobolink. In crossing to South America most of the bobolinks use
route 3 (fig. 17), showing no hesitation in making the flight from
Jamaica across an islandless stretch of ocean. It will be noted that
colonies of these birds have established themselves in western areas,
but in migration they adhere to the ancestral flyways and show no
tendency to take the short cut across Arizona, New Mexico, and Texas.
(See p. 55.)]
Formerly it was thought that most of the North American land birds
that migrate to Central America made a leisurely trip along the
Florida coast, crossed to Cuba, and thence made the short flight
from the western tip of Cuba to Yucatan. A glance at the map would
suggest this as a most natural route, but as a matter of fact it is
practically deserted except for a few swallows and shorebirds, or an
occasional land bird storm-driven from its accustomed course. What
actually happens is that in the fall many of the birds that breed
east of the Allegheny Mountains travel parallel to the seacoast in
a more or less southwesterly direction and, apparently maintaining
this same general course from northwestern Florida, cross the Gulf of
Mexico to the coastal regions of eastern Mexico.
The routes used by the Atlantic brant merit some detail for the
reason that these were long misunderstood. These birds winter on
the Atlantic coast, chiefly at Barnegat Bay, N. J., but (depending
upon the severity of the season and the food available) south also
to North Carolina. Their breeding grounds are in the Canadian arctic
archipelago and on the coasts of Greenland. According to the careful
studies of Lewis (1937), the main body travels northward in spring
along the coast to the Bay of Fundy, hence overland to Northumberland
Strait, which separates Prince Edward Island from the mainland of New
Brunswick and Nova Scotia. A minor route appears to lead northward
from Long Island Sound by way of such valleys as those of the
Housatonic and Connecticut Rivers, and on across southern Quebec to
the St. Lawrence River.
After spending the entire month of May feeding and resting in various
parts of the Gulf of St. Lawrence, the eastern segment of the brant
population suddenly resumes its journey by crossing to the north
shore of the St. Lawrence estuary. The Bay of Seven Islands, in this
general region, is the point of departure for long overland flights
that are made by the two segments of the population. The eastern
and larger of these appears to fly almost due north to Ungava Bay
and from there to nesting grounds, probably in Baffin Island and
Greenland. The smaller segment travels a route that is but slightly
north of west to the southeastern shores of James Bay, although
somewhere to the east of that area some of the flocks take a more
northwesterly course, descending the Fort George River to reach the
eastern shore of James Bay about two-thirds of the distance north of
its southern extremity. Upon their arrival at either of these two
points on James Bay, the brant of this western segment turn northward
and proceed through the eastern part of Hudson Bay to their breeding
grounds, probably in western Baffin Island, Southampton Island, and
other islands in the Canadian Arctic.
In general, the fall migration of the brant follows the routes
utilized in the spring. At this season, when gathering for the
flight of 570 miles to the St. Lawrence River, they appear only on
the western and southern shores of Ungava Bay. Also, it appears that
most of the birds of the western segment, instead of following the
eastern shores of Hudson and James Bays, turn southwestward across
the former, by way of the Belcher Islands, to Cape Henrietta Maria
and from there south along the western shores of James Bay by way of
Akimiski and Charlton Islands. At the southern end of James Bay they
are joined by those that have taken the more direct route along the
east coasts of the bays and all then fly overland 570 miles to the
estuary of the St. Lawrence River.
The Atlantic flyway receives accretions of waterfowl from three or
four interior migration paths, one of which is of first importance,
as it includes great flocks of canvasbacks, redheads, scaup ducks,
Canada geese, and many of the black ducks that winter in the waters
and marshes of the coastal region south of Delaware Bay. The
canvasbacks, redheads, and scaups come from their breeding grounds
on the great northern plains of central Canada, follow the general
southeasterly trend of the Great Lakes, cross Pennsylvania over
the mountains, and reach the Atlantic coast in the vicinity of
Delaware and Chesapeake Bays. Black ducks, mallards, and blue-winged
teals that have gathered in southern Ontario during the fall leave
these feeding grounds and proceed southwest over a course that is
apparently headed for the Mississippi Valley. Many do continue this
route down the Ohio Valley, but others, upon reaching the vicinity
of the St. Clair Flats, between Michigan and Ontario, swing abruptly
to the southeast and, crossing the mountains in a single flight,
reach the Atlantic coast south of New Jersey. This route, with
its Mississippi Valley branch, has been fully demonstrated by the
recovery records of ducks banded at Lake Scugog, Ontario.
The white-winged scoter, which also breeds in the interior of the
continent from northern North Dakota north to the Arctic coast, was
at one time credited with an elliptical migration route, at least
insofar as those wintering on the Atlantic coast are concerned.
This sea duck nests only near fresh water but spends the winters on
the ocean along both the Atlantic and Pacific coasts of the United
States. It migrates over land surfaces mainly at night and it is now
believed that after working northward to the waters of Long Island
Sound it starts up the valleys of the Hudson and Connecticut Rivers
and flies overland to the Great Lakes, from which region it continues
west and northwest to the breeding grounds, returning to its winter
quarters over the same route. Early ideas alleging an elliptical
route probably arose from the fact that great numbers of first-year
nonbreeding birds regularly pass up the New England coast, cross the
Gulf of St. Lawrence and spend the summer loafing off the coast of
Labrador. In the fall these birds form into large flocks and retrace
their flight, chiefly during daylight hours, to winter quarters from
southeastern Maine south at least to Chesapeake Bay. As it was not
known that the white-winged scoter does not usually breed until it is
2 years old, and since the southward movement of yearling birds was
conspicuous while the travels of those from the nesting grounds were
chiefly at night, the theory was advanced that the latter flew 1,500
miles due east from the region west of Hudson Bay to the coast of
Labrador, thence southward to the known winter quarters.
A study of the Canada geese that winter abundantly in the waters of
Back Bay, Va., and Currituck Sound, N. C., reveals another important
tributary to the Atlantic coast route. Banding has shown that the
principal breeding grounds of these birds are among the islands
and on the eastern shore of Hudson Bay. From this region they move
south in autumn to the point of Lower Ontario between Lakes Erie
and Huron. Occasionally one of these geese will be recovered in the
Mississippi Valley but the great majority are retaken either on their
breeding grounds or on the Atlantic coast south of Delaware Bay,
showing another instance of a long cross-country flight by waterfowl.
Although the Canada goose is abundant in migration on the coast of
New England, the birds taken there rarely include any of those banded
in southern Ontario. The northeastern population of these geese comes
from breeding areas in New England, the Maritime Provinces of Canada,
Newfoundland, and the desolate coast of Labrador, their migration
being entirely coastwise. Still another cross-country route between
the Mississippi Valley and the Atlantic coast remains to be briefly
described. It is not yet well understood, but the banding of ducks
such as the blue-winged teal on the coastal saw-grass marshes of
South Carolina has revealed that there is a migration route across
the Appalachians to the Mississippi Valley. Birds marked in these
marshes have been retaken in Tennessee and Kentucky, as well as in
other States farther north in the Mississippi Flyway.
=Mackenzie Valley--Great Lakes--Mississippi Valley route and
tributaries=
Easily the longest route of any in the Western Hemisphere is that
extending from the Mackenzie Valley past the Great Lakes and down the
Mississippi River, including its tributaries. Its northern terminus
is on the Arctic coast in the regions of Kotzebue Sound, Alaska,
and the mouth of the Mackenzie River, while its southern end lies
in Patagonia. During the spring migration some of the shore birds
traverse the full extent of this great path, and it seems likely
that the nighthawk, the barn swallow, the blackpolled warbler, and
individuals of several other species that breed north to Yukon and
Alaska must twice each year cover the larger part of it.
For more than 3,000 miles--from the mouth of the Mackenzie to the
delta of the Mississippi--this route is uninterrupted by mountains.
In fact, there is not even a ridge of hills high enough to interfere
with the movements of the feathered travelers, and the greatest
elevation above sea level is less than 2,000 feet. Well timbered and
watered, the entire region affords ideal conditions for the support
of its great hosts of migrating birds. It is followed by such vast
numbers of ducks, geese, shore birds, blackbirds, sparrows, warblers,
and thrushes, that observers stationed at favorable points in the
Mississippi Valley daring the height of migration can see a greater
number of species and individuals than can be noted anywhere else in
the world.
Starting in the region of Kotzebue Sound, Alaska, the route extends
eastward across northern Alaska and joins another that has its origin
at the mouth of the Mackenzie River. The line of flight then trends a
little east of south through the great lake system of central Canada,
where it is joined by two or three other routes from the northeast
that have their origin on the central Arctic coast. Continuing
southward the migrating flocks are constantly augmented by additions
to their numbers as they pass over the great breeding grounds of
central and southern Canada. Upon reaching the headwaters of the
Missouri and Mississippi Rivers the route follows these streams to
the Gulf coast, Arriving in this latitude many species, including
the ducks and geese, the robin, the myrtle warbler, and some others
spread out east and west for their winter sojourn. Others, despite
the perils of a trip involving a flight of several hundred miles
across the Gulf of Mexico, strike out boldly for Central America
and South America. This part of the route is a broad "boulevard"
extending from northwestern Florida to eastern Texas and reaching
southward across the Gulf of Mexico to Yucatan and the Isthmus of
Tehuantepec (fig. 17, route 4). In other words, when most of the
birds (chiefly shore birds and land birds) that have come south
directly through the Mississippi Valley have reached the coastal
plains of Mississippi and Louisiana, they continue directly across
the Gulf of Mexico. This route appears to have preference over the
safer but more circuitous land or island routes by way of Texas and
Florida. During the height of migration some of the islands off the
coast of Louisiana are wonderful observation points for the student
of birds, as the feathered travelers literally swarm over them.
Present detailed knowledge of the chief tributaries to the
Mackenzie--Great Lakes--Mississippi Valley highway relates chiefly
to waterfowl. Reference already has been made to the flight of the
black ducks (p. 58) that reach the Mississippi Valley from southern
Ontario. Some individuals of this species banded at Lake Scugog,
Ontario, have been recaptured in succeeding seasons in Wisconsin
and Manitoba, but the majority have been retaken at points south
of the junction of the Ohio River with the Mississippi, definitely
indicating their route of travel from southern Ontario.
A second route that joins the main artery on its eastern side is
the one used by the blue goose, the migration route of which is
probably more nearly due north and south than that of any other
North American bird. The breeding grounds, which only in recent
years have been discovered, are mainly in the Fox Basin region of
Baffin Island and on Southampton Island. In fall these geese work
southward, chiefly along the eastern shore of Hudson Bay, and upon
reaching the southern extremity of James Bay they take off for what
is practically a nonstop flight to the great coastal marshes of
Louisiana west of the delta of the Mississippi River. In some seasons
the flocks make intermediate stops among the islands and sand bars
of the Mississippi, as they are occasionally common in the general
vicinity of Memphis, Tenn. Most of the birds push on, however, and
during the period from the first of November to the last of March
fully 90 percent of the species are concentrated in the area between
the Sabine and the Mississippi Rivers. On the return trip northward
there is sometimes a tendency for some of the blue geese to veer off
toward the northwest, as they are occasionally abundant in eastern
South Dakota and southeastern Manitoba. It is of particular interest
to note that while some other geese and many ducks start their
northward journey at the first sign of awakening spring, the blue
goose remains in its winter quarters until the season there is far
advanced, seemingly aware that its own breeding grounds in the Arctic
are still in the grip of winter.
=Great Plains--Rocky Mountain routes=
A great western highway also has its origin in the Mackenzie River
delta area and in Alaska. This is used chiefly by the pintail and the
American widgeon or baldpate, which fly southward through eastern
Alberta to western Montana. Some localities in this area, as for
example, the National Bison Range at Moiese, Mont., normally furnish
food in such abundance as to induce these birds to pause in their
migratory movement. Upon resuming travel, some flocks move almost
directly west across Idaho to the valley of the Columbia River, from
which they turn abruptly south to the interior valleys of California.
Others leave the Montana feeding and resting areas and turn
southeastward across Wyoming and Colorado to join the flocks that are
moving southward through the Great Plains (fig. 15).
Many redheads that breed in the Bear River marshes in Utah take a
westerly route across Nevada to California, but some leave these
breeding grounds and fly northeastward across North Dakota and
Minnesota to join the flocks of these ducks that come out of the
prairie regions of Canada. A few of them even travel southeastward to
the Atlantic coast. This route can be traced by the records of ducks
banded in summer in the Bear River marshes and retaken the following
fall at points in eastern Montana, Wyoming, South Dakota, North
Dakota, Minnesota, Wisconsin, Michigan, Ohio, and Maryland. Great
numbers, however, follow another route from these marshes across the
mountains in an easterly direction, where it almost immediately turns
southward through Colorado and New Mexico, and continues to winter
quarters in the Laguna Madre off the coast of Texas or in the Valley
of Mexico (fig. 17, route 6). This route also represents the travels
of many of the land birds of the Rocky Mountain region. Such birds
perform comparatively short migrations, most of them being content
to stop when they reach the middle districts of Mexico, only a few
passing beyond the southern part of that country.
Observations made in the vicinity of Corpus Christi, Tex., have
shown one of the short cuts (fig. 17, route 5) that is, in effect,
a part of the great artery of migration. Thousands of birds pass
along the coast to the northern part of the State of Vera Cruz. As
the coast of the State of Tamaulipas to the north is arid and so
entirely unsuited to the needs of birds that are frequenters of moist
woodlands, it is probable that much or all of this part of the route
is a short distance off shore. It is used by such woodland species as
the golden-winged warbler, the worm-eating warbler, and the Kentucky
warbler.
=Pacific coast route=
Although it does present features of unusual interest, the Pacific
coast route is not of so great importance as some of the others
described. Because of the equable conditions that prevail, many
species of birds along the coast from the Northwestern States to
southeastern Alaska either do not migrate at all or else make
relatively short journeys. This route has its origin chiefly in
Alaska, the general region of the delta of the Yukon River marking
its northern terminus, although a few species join it after a flight
westward along the Alaskan Arctic coast. Some of the scoters and
other sea ducks of the north Pacific region, and the diminutive
cackling goose which breeds in the delta of the Yukon River, use the
coastal sea route for all or most of their southward flight. The
journey of the cackling goose, as shown by return records from birds
banded at Hooper Bay, Alaska, has been traced southward across the
Alaska Peninsula and apparently across the Gulf of Alaska to the
Queen Charlotte Islands, the birds following the coast line south
to near the mouth of the Columbia River. There the route swings
toward the interior for a short distance before continuing south
by way of the Willamette River Valley. The winter quarters of the
cackling goose are chiefly in the vicinity of Tule Lake, on the
Oregon-California line, and in the Sacramento Valley of California,
though a few push on to the San Joaquin Valley.
[Illustration: _Figure 20._--The breeding range, winter range, and
migration route of Ross's goose. This is the only species of which
all members apparently breed in the Arctic regions, migrate south
through the Mackenzie Valley, and upon reaching the United States,
turn to the southwest rather than the southeast. The southern part
of this route, however, is followed by some mallards, pintails,
baldpates, and possibly by other ducks.]
A tributary of this flyway is followed by Ross's goose which is now
known to breed only in the Perry River district south of the Queen
Maud Gulf on the central Arctic coast of Canada (fig. 20). Its fall
migration appears to be southwest and south across the barren grounds
to Great Slave and Athabaska Lakes, where it joins thousands of other
waterfowl bound for their winter homes along the eastern coast of the
United States and the Gulf of Mexico. But when the Ross's geese have
traveled south approximately to the northern boundary of Montana,
they separate from their companions, and turning to the southwest
cross the Rocky Mountains and settle for the winter in California.
[Illustration: _Figure 21._--Breeding and wintering ranges of the
western tanager. See figure 22 for the spring route taken by the
birds breeding in the northern part of the range.]
The route taken by the white-winged scoters that winter on the
Atlantic coast already has been indicated (p. 59). Some birds of this
species, however, winter on the Pacific coast from Puget Sound south
to southern California. Their passage by thousands up and down the
coast has been noted as far north as northwestern British Columbia.
The species is known to nest in Alaska, which may be the home of
some, at least, of the scoters that winter on the Pacific coast. If
such be the case, however, it must be admitted that a part of the
route taken by the birds when on migration is unknown, though very
few observations are available from the interior of northern British
Columbia, across which the route may lie.
The southward route of those migratory land birds of the Pacific
coast that in winter leave the United States extends chiefly through
the interior of California to the mouth of the Colorado River and on
to winter quarters in western Mexico.
The movements of the western tanager show a migration route that is
in some ways remarkable. The species breeds in the mountains from
the northern part of Baja California and western Texas north to
northeastern British Columbia and southwestern Mackenzie. Its winter
range is in two discontinuous areas--southern Baja California and
eastern Mexico south to Guatemala (fig. 21). On the spring migration
the birds enter the United States about April 20, appearing first in
western Texas and the southern parts of New Mexico and Arizona (fig.
22). By April 30 the vanguard has advanced evenly to an approximate
east-and-west line across central New Mexico, Arizona, and southern
California. But by May 10 the easternmost birds have advanced only to
southern Colorado, while those in the far west have reached northern
Washington. Ten days later the northward advance of the species is
shown as a great curve, extending northeastward from Vancouver Island
to central Albert and thence southeastward to northern Colorado.
Since these tanagers do not reach northern Colorado until May 20,
it is evident that those present in Alberta on that date, instead
of traveling northward through the Rocky Mountains, which from the
location of their summer and winter homes would seem to be the
natural route, reached there by the Pacific coast route to southern
British Columbia and thence across the mountains, despite the fact
that these are still partly covered with snow at that time.
=Pacific oceanic route=
The route of the Pacific golden plover is fully as interesting and as
remarkable as the elliptical course followed by its eastern cousin
(fig. 18). The breeding range of the eastern golden plover extends
through Arctic America west to the northern coast of Alaska where,
in the vicinity of Point Barrow, it meets the nesting grounds of
the Pacific form, which is really an Asiatic subspecies. It breeds
chiefly in the Arctic coast region of Siberia and merely overflows
onto the Alaskan coast, some of the birds probably migrating south
along the coast of Asia to winter quarters in Japan, China, India,
Australia, New Zealand, and Oceania, including the Hawaiian Islands,
the Marquesas Islands, and the Low Archipelago. Golden plovers in
migration have been observed at sea on a line that apparently extends
from these islands to the Aleutians, and it therefore appears certain
that at least some of the Alaskan birds make a nonstop flight across
a landless sea from Alaska to Hawaii. While it would seem incredible
that any birds could lay a course so straight as to attain these
small oceanic islands, 2,000 miles south of the Aleutians, 2,000
miles west of Baja California, and nearly 4,000 miles east of Japan,
the evidence admits only the conclusion that year after year this
transoceanic round-trip journey between Alaska and Hawaii is made by
considerable numbers of golden plovers.
[Illustration: _Figure 22._--Migration of the western tanager.
The birds that arrive in eastern Alberta by May 20 do not travel
northward along the eastern base of the Rocky Mountains, as in that
region the van has then only reached northern Colorado. Instead the
isochronal lines indicate that they migrate north through California,
Oregon, and Washington, and then cross the mountains of British
Columbia.]
The Pacific oceanic route probably is used also by the arctic terns
that breed in Alaska, and possibly by those from the more western
tern colonies of Canada. This species is of regular occurrence on
the western coasts of both the United States and South America,
indicating that the western representatives travel southward to the
Antarctic winter quarters without the spectacular migration features
that appear to characterize the flight of those from the eastern part
of the continent (fig. 8).
=Arctic routes=
In the discussion of the migration of the Arctic tern (p. 38) it was
noted that this species makes a very distinct west-to-east movement
across northern Canada, continuing the flight eastward across the
Atlantic Ocean toward the western coast of Europe. It seems likely
that there are other species, including the parasitic jaeger, that
regularly breed in the northern part of the Western Hemisphere but
migrate back to the Old World for their winter sojourn. Some others,
as the red-legged kittiwake and Ross's gull, remain near the Arctic
region throughout the year, retreating southward in winter only a few
hundred miles. The emperor goose in winter is found only a relatively
short distance south of its breeding grounds, and eider ducks,
although wintering in latitudes well south of their nesting areas,
nevertheless remain farther north than do the majority of other
species of ducks.
The routes followed by these birds are chiefly coastwise, and in the
final analysis may be considered as being tributary either to the
Atlantic or to the Pacific coast routes. The passage of gulls, ducks,
the black brant, and other water birds at Point Barrow, Alaska,
and at other points on the Arctic coast, has been noted by several
observers, and from present knowledge it may be said that the best
defined Arctic route in North America is the one that follows around
the coast of Alaska.
[Illustration: _Figure 23._--Distribution and migration of the
red-eyed vireo. It is evident that the red-eyed vireo has only
recently invaded Washington by an extension of its breeding range
almost due west from the upper Missouri Valley. Like the bobolink,
however (fig. 19), the western breeders do not take the short cut
south or southeast from their nesting grounds, but migrate spring and
fall along the route traveled in making this extension.]
_Evolution of Migration Routes_
From the foregoing descriptions of migration routes it will be
observed that the general trend of migration in most species of North
American birds is northwest and southeast. It is comparatively easy
to trace the probable steps in the evolution of the migrations of
some species, and some routes have developed so recently that they
still plainly show their origin.
The tendency is for eastern species to extend their ranges by pushing
westward, particularly in the north. For example, in the Stikine
River Valley of northern British Columbia and southwestern Alaska the
eastern nighthawk, eastern chipping sparrow, rusty blackbird, eastern
yellow warbler, redstart, and others have established breeding
stations at points 20 to 100 miles from the Pacific Ocean. The robin,
flicker, slate-colored junco, blackpolled and myrtle warblers,
and ovenbird, all common eastern species, also are established as
breeding birds in western Alaska, the ovenbird having been detected
on the lower Yukon River. These birds are essentially Atlantic and
Mississippi Flyway species, however, and so do not migrate in fall
by any of the Pacific or Central routes, but instead retrace their
journey across the mountains and move southward along the broad
flyways of the East.
The red-eyed vireo, a striking example of an abundant woodland bird,
is essentially an inhabitant of States east of the Great Plains, but
an arm of its breeding range extends northwest to the Pacific coast
in British Columbia (fig. 23). It seems evident that this is a range
extension that has taken place comparatively recently by a westward
movement from the upper Missouri Valley, and that the invaders
retrace in spring and fall the general route by which they originally
entered the country.
In the case of the bobolink, a new extension of the breeding range,
and a consequent change in the migration of the species, has taken
place since the settlement of the country (fig. 19). A bird of damp
meadows, it was originally cut off from the Western States by the
intervening arid regions. But with the advent of irrigation and the
bringing of large areas under cultivation, small colonies of nesting
bobolinks have appeared at various western points, and now the
species is established as a regular breeder in the great mountain
parks and irrigated valleys of Colorado and elsewhere almost to the
Pacific coast. In retracing their course to reach the western edge
of the route followed by the bulk of the bobolinks that breed in the
northern United States and southern Canada, these western pioneers
must fly long distances along a line that runs almost due east and
west.
Similarly it is possible to sketch what seems to be the logical
evolution of the remarkable routes of the golden plover (fig. 18). It
may be assumed that the eastern birds of this species first followed
an all-land route from the South American winter quarters through
Central America, Mexico, and Texas to the western parts of the
Mississippi Valley. As the migration route lengthened northward with
the retreat of the ice and the bird's powers of flight developed,
there would be a tendency to straighten the line and to shorten it
by cutting off some of the great curve through Mexico and Texas.
First a short flight across the western part of the Gulf of Mexico
was probably essayed. Proving successful, this was followed by flight
lines that moved farther east, until finally the roundabout curve
through Texas was entirely discarded and the flight made directly
across the Gulf to southern Louisiana.
As the great areas in Canada were gradually added to the birds'
domain, other important factors arose, the chief being the
attractiveness of the vast stretches of coast and plain of the
Labrador Peninsula, which in fall offered a bountiful store of
berries. The fall route therefore worked eastward to the Gulf of
St. Lawrence, thence southwest along the coast to Florida and
across the Gulf of Mexico to the Central American mainland. A
series of shortening flights followed to take out the great curve
of the Atlantic coast. A relatively short ocean flight was probably
attempted, say from Cape Cod to the Bahama Islands, Cuba, and
Jamaica, followed eventually by the long direct oceanic route as it
is now known.
As the Labrador Peninsula in spring is bound by frost and shrouded
in fog while the season advances rapidly through the interior, the
oceanic route proved useful only in fall, and the spring flight
continued through the Mississippi Valley. This outline, although
entirely hypothetical, gives a probable and fairly plausible
explanation of the origin of this wonderful route, particularly
when it is remembered that migration routes as now known are
evolutions--age-long modifications of other routes.
The evolution of the migration route of the Pacific golden plover
may be explained in a similar fashion. At first the route probably
followed the Asiatic coast, through the Malay Peninsula and Oceania,
thence east in a great curve to the Low Archipelago, with individuals
and flocks dropping out to winter at many points along the way. The
Siberian birds probably continue to follow this ancient highway, but
those nesting in Alaska began a long evolutionary series of flights
that cut down the length of their journey by shortening the curve,
until finally the transoceanic route of the present day was developed.
This theory of the evolution of migration routes has been questioned
by some ornithologists on the ground that it implies the possession
in some degree of reasoning powers such as would be used by human
beings. This opposition suggests that changes in migration routes
might develop suddenly following mass survival of birds that were
driven over the new route by a storm on some specific occasion.
In the language of genetics, the new route would be, in effect, a
mutation, rather than the result of an accumulation of infinitesimal
variations. There is some evidence in support of this opposing
theory. For example, information from the Hudson's Bay Co. post at
Great Whale River, on the southeastern coast of Hudson Bay, indicates
that in 1884 the snow geese suddenly changed their route from the
eastern to the western coasts of Hudson and James Bays. According to
one report, this change was caused by strong winds from the south
which caught the birds in their fall migration and caused them to
cross the entrance of James Bay from Cape Jones to the western
side; the route thus reportedly forced upon them was then used in
succeeding years.
_Vertical Migration_
In the effort to find winter quarters furnishing satisfactory living
conditions, many North American birds fly hundreds of miles across
land and sea. Others, however, are able to attain their objective
merely by moving down the sides of a mountain. In such cases a few
hundred feet of altitude correspond to hundreds of miles of latitude.
Movements of this kind, known as "vertical migrations," are found
wherever there are large mountain ranges. In the Rocky Mountain
region they are particularly notable, as chickadees, rosy finches,
juncos, pine grosbeaks, and some other species that nest in the
Alpine Zone move down to the lower levels to spend the winter. It
has been noted that such species as Williamson's sapsucker and the
western wood pewee, which nest in the higher mountains, move down
to the lower regions in August following the breeding season. There
is a distinct tendency among the young of mountain-breeding birds to
work down to the lower levels as soon as the nesting season is over.
The sudden increases among birds in the edges of the foothills are
particularly noticeable when cold spells with snow or frost occur at
the higher altitudes.
Some species that normally breed in the Hudsonian or Arctic Zones
find suitable breeding areas on the higher levels of the mountains,
as for example the pipit, or titlark, which breeds on the tundra of
Alaska and northern Canada and also south as far as Colorado on the
summits of many peaks in the Rocky Mountains. On the other hand, a
few species, as the Clark's crow, or nutcracker, nest at relatively
low altitudes in the mountains and as the summer advances move
higher up, thus performing a vertical migration that in a sense is
comparable with the post-breeding movements of herons on the Atlantic
coast. These illustrations show that the length of a migration route
may depend upon factors other than latitude.
_Vagrant Migration_
The most striking feature of the migrations of some of the herons
is a northward movement after the nesting season. The young of some
species commonly wander late in the summer and in fall, sometimes
traveling several hundred miles north of the district in which they
were hatched. The little blue heron breeds commonly north to South
Carolina, and by the last of July the young birds begin to appear
along the Potomac, Patuxent, and Susquehanna Rivers, tributary to
Chesapeake Bay. Although almost all are immature individuals, as
shown by their white plumage, an occasional adult may be noted. With
them come egrets and snowy herons and on occasion all three species
will travel in the East as far north as New England, and in the
Mississippi Valley to southeastern Kansas and Illinois. In September
most of them disappear, probably returning south by the same route.
The black-crowned night heron has similar wandering habits, and
young birds banded in a large colony at Barnstable, Mass., have
been recaptured the same season north to Maine and Quebec and west
to New York. This habit seems to be shared by some of the gulls
also, although here the evidence is not so conclusive. Herring gulls
banded as chicks at colonies in the Great Lakes have scattered in
all directions after the breeding season, some having been recovered
well north in Canada.
These movements may be considered as migration governed only by
the availability of food, and they are counteracted in fall by a
directive migratory impulse that carries back to their normal winter
homes in the south those birds that after the nesting period attained
more northern latitudes. They are not to be compared with the great
invasions of certain birds from the North. Classic examples of the
latter in the eastern part of the country are the periodic flights of
crossbills. Sometimes these migrations will extend well south into
the Carolinian Zone.
Snowy owls are noted for occasional invasions that have been
correlated with the periodic maximum of Arctic foxes and the lemming
cycle in the north. According to Gross (1947) 24 major invasions
occurred between 1833 and 1945. The interval between these varied
from 2 to 14 years, but nearly half (11) were at intervals of 4
years. A great flight occurred in the winter of 1926-27 when more
than 1,000 records were received from New England alone, but the
largest on record was in 1945-46 when the "Snowy Owl Committee"
of the American Ornithologists' Union received reports of 13,502
birds, of which 4,443 were reported as killed. It extended over the
entire width of the continent from Washington and British Columbia
to the Atlantic coast and south to Nebraska, Illinois, Indiana,
Pennsylvania, and Maryland. One was taken as far south as South
Carolina.
In the Rocky Mountain region great flights of the beautiful Bohemian
waxwing are occasionally recorded. The greatest invasion in the
history of Colorado ornithology occurred in February 1917, at which
time the writer estimated that at least 10,000 were within the
corporate limits of the city of Denver. The last previous occurrence
of the species in large numbers in that section was in 1908.
Evening grosbeaks likewise are given to performing more or less
wandering journeys, and curiously enough, in addition to occasional
trips south of their regular range, they travel east and west,
sometimes covering long distances. For example, grosbeaks banded at
Sault Ste. Marie, Mich., have been recaptured on Cape Cod, Mass., and
in the following season have been retrapped at the banding station.
Banding records demonstrate that this east-and-west trip across the
northeastern part of the country is sometimes made also by purple
finches.
_Perils of Migration_
The period of migration is a season full of peril for birds. Untold
thousands of the smaller migrants are destroyed each year by storms
and through attacks of predatory birds, mammals, and reptiles. If
each pair of adult birds should succeed in raising two fledglings to
maturity, the population of migratory birds would have a potential
annual increase of 100 percent and the world would soon be heavily
overpopulated with them. Since there is no such increase it is
evident that the annual mortality from natural causes is heavy enough
to keep it in check.
=Storms=
Of the various factors limiting the abundance of birds, particularly
the smaller species, storms are the most potent. Special sufferers
are those birds that in crossing broad stretches of water are forced
down by a storm within reach of the waves. Such a catastrophe was
once seen from the deck of a vessel in the Gulf of Mexico, 30 miles
off the mouth of the Mississippi River. Great numbers of migrating
birds, chiefly warblers, had accomplished nearly 95 percent of
their long flight and were nearing land, when, caught by a norther
against which they were unable to contend, hundreds were forced into
the waters of the Gulf and drowned. On another occasion, on Lake
Michigan, a severe storm came up at a time when large numbers of
migratory birds were crossing and forced numerous victims into the
waves. During the fall migration of 1906, when thousands of birds
were crossing Lake Huron, a sudden drop in temperature accompanied
by a heavy snowfall resulted in the death of incredible numbers.
Literally thousands were forced into the water and subsequently cast
up along the beaches, where in places their bodies were piled in
windrows. On one section of the beach the dead birds were estimated
at 1,000 per mile, and at another point at 5 times that number. Most
of them were species that rank among our most desirable birds as
destroyers of insects and weed seeds, including slate-colored juncos,
tree sparrows, white-throated sparrows, swamp sparrows, winter wrens,
and golden-crowned kinglets, together with many brown creepers,
hermit thrushes, warblers, vireos, and others.
Of all species of North American birds, the Lapland longspur seems to
be the most frequent victim of mass destruction from storms. These
birds sometimes congregate in enormous numbers where grass or weed
seed is abundant. Almost every winter brings in reports of their
death by thousands somewhere in the Middle West. While migrating
northward at night they have encountered blinding storms of wet,
clinging snow, which have so bewildered them that they have flown
into various obstructions, or have sunk to the ground and perished
of exposure and exhaustion. In 1907 an experienced ornithologist
estimated that 750,000 longspurs were lying dead on the ice of 2
lakes in Minnesota, each about 1 square mile in extent, and dead
birds were reported in greater or less abundance on this occasion
over an area of more than 1,500 square miles. The heaviest mortality
occurred in towns, where, bewildered by the darkness and the heavy
falling snow, some of the birds congregating in great numbers flew
against various obstacles and were killed or stunned, while many
others fell to the ground exhausted. Similar catastrophes have been
reported from eastern Colorado, Nebraska, and North Dakota.
During the early part of June 1927, a hailstorm of exceptional
severity in and around Denver, Colo., killed large numbers of robins,
meadow larks, sparrows, and others. The lawns of parks were strewn
with the bodies of these birds, and many lay dead in their nests
where they were covering their eggs or young when the storm broke.
=Aerial obstructions=
Lighthouses, lightships, tall bridges, piers, monuments, and
other aerial obstructions have been responsible for a tremendous
destruction of migratory birds. Beams of the lanterns at light
stations have a powerful attraction for nocturnal travelers of the
air that may be likened to the fascination for lights that also
is shown by many insects, particularly night-flying moths. The
attraction is not so potent in clear weather, but when the atmosphere
is moisture laden, as in a heavy fog, the rays have a dazzling effect
that lures the birds to their death. They may fly straight up the
beam and dash themselves headlong against the glass, or they may keep
fluttering around the source of the light until exhausted, and then
drop to the rocks or waves below. The fixed, white, stationary light
located 180 feet above sea level at Ponce de Leon Inlet (formerly
Mosquito Inlet), Fla., has caused great destruction of bird life
even though the lens is shielded by wire netting. On one occasion an
observer gathered up a bushel-basketful of warblers, sparrows, and
other small passerine birds that had struck during the night. The
birds apparently beat themselves to death against the wire or fell
exhausted to the concrete pavement below, frequently to be destroyed
there by cats or skunks. Two other lighthouses at the southern end
of Florida, Sombrero Key and Fowey Rocks, have been the cause of
a great number of bird tragedies, while heavy mortality has been
noted also at some of the lights on the Great Lakes and on the coast
of Quebec. It is the fixed white lights that cause such disasters
to birds, as the stations equipped with flashing or red lights do
not present such strong attractions. That it is not a mere case of
geographical location has been demonstrated, for it is observed that
when fixed white lights have been changed to red or flashing lights,
the migrating birds are no longer endangered. At some of the light
stations in England and elsewhere, shelves and perches have been
placed below the lanterns to afford places where birds can rest until
they have overcome their bewilderment.
For many years at the National Capital, the Washington Monument,
although unilluminated, caused the destruction of large numbers of
small birds, due apparently to their inability to see this obstacle
in their path, towering more than 555 feet into the air. One morning
in the spring of 1902 the bodies of nearly 150 warblers, sparrows,
and other birds were found about its base. Then, as the illumination
of the city was improved and the Monument became more visible at
night, the loss became steadily less, until by 1920 only a few birds
would be killed during an entire migration. On November 11, 1931,
however, as part of the Armistice Day celebration, batteries of
brilliant floodlights grouped on all four sides about the base of the
Monument were added to the two searchlights already trained on the
apex, so that the lighted shaft probably corresponds in brilliancy
to a very low magnitude lighthouse lantern. Airplane pilots have
ventured opinions that on a clear night it could be seen for 40
miles. It is certain that there is an extensive area of illumination,
and on dark nights, when there are gusty, northerly winds and the
nocturnal travelers seem to fly at lower altitudes, many of them are
attracted to the Monument as to a lighthouse beacon. As they approach
from the north a last-minute attempt to avoid it causes them to
veer off to the east or the west where they are literally sucked in
and dashed against the southern face of the shaft. During the fall
migration of 1932 more than 500 warblers, vireos, thrushes, kinglets,
sparrows, and others were killed. Since that year the mortality has
been less, but the Monument at times remains a serious menace to
birds during migration and some are killed nearly every fall.
When the torch on the Statue of Liberty in New York Harbor was kept
lighted, it caused an enormous destruction of bird life, tabulations
showing as many as 700 birds killed in a single month.
In September 1948, bird students were startled by news of the
wholesale destruction of Maryland yellowthroats, redstarts,
ovenbirds, and others that were dashed against the 1,250-foot
high Empire State Building in New York City, the 491-foot high
Philadelphia Saving Fund Society Building in Philadelphia, and the
450-foot high WBAL radio tower in Baltimore. In New York the birds
continued to crash into the Empire State Building over a 6-hour
period and their bodies were scattered over a four-block area. The
mortality was so heavy in Philadelphia that it was impossible to
use the sidewalk below the sky-scraper until the birds had been
gathered. A study of the weather conditions prevailing at this
time in the Atlantic coastal region suggests the probable cause
of this catastrophe. By early morning on September 11 a mass of
cold, southward-flowing air had just reached New York City where
it was forcing upward and was being overridden by a mass of warm,
northward-flowing air. Presumably the migrants were riding the upper
levels of the southbound current which, in the contact zone with the
northbound current, was being deflected earthward, thus causing the
birds to fly lower and lower until they were below the tower of the
Empire State Building. Clouds and gusty winds in the zone of contact
between the two air masses reduced visibility and disrupted avian
navigation with the result that the confused travelers crashed into
the stone and steel obstruction. As the cold air mass continued to
move southward, the situation was repeated at Philadelphia and at
Baltimore.
=Exhaustion=
Although it would seem that the exertion incident to the long
flights of many species of migratory birds would result in their
arrival at their destination in a state bordering on exhaustion,
this is contrary to the truth. Both the soaring and the sailing of
birds show them to be proficient in the use of factors employed in
aerial transportation that only recently have become understood and
imitated by aeronautical engineers. The use of ascending currents
of air, employed by all soaring birds, and easily demonstrated by
observing the gulls that glide hour after hour along the windward
side of a ship, are now utilized by man in his operation of gliders.
Moreover, the whole structure of a bird renders it the most perfect
machine for extensive flight that the world has ever known. Hollow,
air-filled bones, making an ideal combination of strength and
lightness, and the lightest and toughest material possible for
flight in the form of feathers, combine to produce a perfect flying
machine. Mere consideration of a bird's economy of fuel or energy
also is enlightening. The golden plover, traveling over the oceanic
route, makes the entire distance of 2,400 miles from Nova Scotia to
South America without stop, probably requiring about 48 hours of
continuous flight. This is accomplished with the consumption of less
than 2 ounces of fuel in the form of body fat. To be as economical in
operation, a 1,000-pound airplane would consume in a 20-mile flight
not the gallon of fuel usually required, but only a single pint.
The sora, or Carolina rail, which is such a notoriously weak flyer
that at least one writer was led to infer that most of its migration
was made on foot, has one of the longest migration routes of any
member of the family, and easily crosses the wide reaches of the
Caribbean Sea. The tiny ruby-throated hummingbird crosses the Gulf of
Mexico in a single flight of more than 500 miles.
While birds that have recently arrived from a protracted flight
over land or sea sometimes show evidences of being tired--as, for
example, pintail ducks that have flown from the North American
mainland to the Hawaiian Islands--their condition is far from being
a state of exhaustion. With a few hours' rest and a crop well
filled with proper food, most birds exhibit eagerness to resume
their journey. The popular notion that birds find the long ocean
flights excessively wearisome and that they sink exhausted when
terra firma is reached, generally does not agree with the facts.
The truth lies in the opposite direction, as even small land birds
are so little averse to ocean voyages that they not only cross the
Gulf of Mexico at its widest point, but may even pass without pause
over the low, swampy coastal plain to the higher regions beyond.
Under favorable conditions birds can fly when, where, and how they
please. Consequently the distance covered in a single flight is
governed chiefly by the food supply. Exhaustion, except as the result
of unusual factors, cannot be said to be an important peril of
migration.
_Influence of the Weather on Migration_
The state of the weather at any point has little if anything to do
with the time of arrival of migratory birds. This is contrary to the
belief of observers who have thought that they could foretell the
appearance of various species by a study of the weather conditions.
Though the insistent crescendo note of the ovenbird is ordinarily
associated with the full verdure of May woods, this bird has been
known to reach its breeding grounds in a snowstorm and the records
of its arrival in southern Minnesota show a temperature variation
from near freezing to full summer warmth. Temperatures at arrival of
several other common birds vary from 14 degrees between highest and
lowest temperatures to 37 degrees, the average variation being about
24 degrees.
It should be remembered that North American species spending the
winter months in tropical latitudes experience no marked changes in
climatic conditions from November to March or April, yet frequently
they will start the northward movement in January or February. This
is in obedience to physiological promptings and has no relation to
the prevailing weather conditions. For migratory birds the winter
season is a period of rest, a time when they have no cares other
than those associated with the daily search for food or escape from
their natural enemies. Their migrations, however, are a vital part
of their life cycles, which have become so well adjusted that the
seasons of travel correspond in general with the major seasonal
changes on their breeding grounds. With the approach of spring,
therefore, the reproductive impulse awakens, and each individual bird
is irresistibly impelled to start the journey that ends in its summer
home.
In other words, the evidence indicates that the urge to migrate
is so ingrained that each species moves north in spring when the
average weather that will be encountered is not unendurable. The
word "average" must be emphasized since it appears obvious that the
migrations of birds have so evolved that in general they synchronize
with average climatic conditions. The hardy species travel early,
fearless of the blasts of retreating winter, while the more delicate
kinds come later when there is less danger of encountering prolonged
periods of inclement weather. Some of the hardy birds pause in
favorable areas and allow the spring season to advance. Then, by
rapid travel they again overtake it, or, as sometimes happens, they
actually outstrip it. Occasionally this results in some hardship,
and rarely in the destruction of large numbers of individuals. Cases
are known where early migrating bluebirds have been overwhelmed by
late winter storms. Nevertheless, unless such climatic conditions are
prolonged, no serious effect on the species is noted. The soundness
of the bird's instincts is evidenced by the fact that natural
catastrophes, great though they may be, do not permanently diminish
the avian populations.
As has been pointed out, the advance of average temperature lines,
known as isotherms, is found to correspond closely with the northward
movements of certain species. For example, the northward travels
of the Canada goose are found to coincide with the advance of the
isotherm of 35° F. (fig. 4).
The spring flight of migrants, if interrupted for any reason, is
resumed when weather conditions again become favorable, and it is
probable that all instances of arrival of birds in stormy weather
can be explained on the theory that the flight was begun while the
weather was auspicious. The state of the weather when a flight starts
at any southern point, the relation of that place to the average
position of the bird under normal weather conditions on that date,
and the average rate of migratory flight, are data basic to any
reasonably accurate prediction of the time arrival may be expected in
northern areas.
Head winds are as unfavorable to migration as is rain or snow, as
they greatly increase the labor of flight and cut down the speed of
cross-country travel. If such winds have a particularly high velocity
they may force down the weaker travelers, and when this happens over
water areas, large numbers of birds are lost. Even strong winds that
blow in the direction of aerial travel are unfavorable for the birds,
as they interfere with their balance and disarrange their feathers.
Moderate tail winds and cross or quartering breezes appear to offer
the best conditions for the passage of the migrants.
_Problems of Migration_
=Banding studies=
The study of living birds by the banding method, whereby great
numbers of individuals are marked with numbered aluminum leg rings,
has come to be recognized as a most accurate means of ornithological
research. Since 1920, banding work in North America has been under
the direction of the Fish and Wildlife Service in cooperation
with the Dominion Wildlife Service of Canada. Every year voluntary
cooperators, working under permit, place bands on thousands of birds,
game and nongame, large and small, migratory and nonmigratory,
each band carrying a serial number and the legend, NOTIFY FISH AND
WILDLIFE SERVICE, WASHINGTON, D. C., or on the smaller sizes an
abbreviation thereof. When a banded bird is reported from a second
locality, a definite fact relative to its movements becomes known,
and a study of many cases of this nature develops more and more
complete knowledge of the details of migration.
The records of banded birds are also yielding other pertinent
information relative to their migrations, such as the exact dates
of arrival and departure of individuals, the length of time that
different birds pause on their migratory journeys to feed and rest,
the relation between weather conditions and the starting times for
migration, the rates of travel of individual birds, the degree of
regularity with which birds return to the exact summer or winter
quarters used in former years, and many other details that could
be learned in no other manner. Banding stations that are operated
systematically throughout the year, therefore, are supplying much
information concerning the movements of migratory birds that
heretofore could only be surmised. (See Appendix II, p. 92 for
instructions on reporting the recovery of banded birds.)
=Movements of residents=
Typical migration consists of definite movements that are repeated
regularly year after year, and it is to these that the term is
generally restricted. It is desirable, however, if only for purposes
of comparison, that some account be taken of the movements of some
other birds, which, while not typical, do possess some of the
characteristics of true migration. Data on this subject are being
collected through bird banding.
There are several species that are customarily grouped under the
heading "permanent residents," the term implying that these birds
do not travel but remain throughout the year in one locality.
Among these are the cardinal, the tufted titmouse, the wrentit,
the Carolina wren, the house finch, the bobwhite, the California
quail, and the ruffed grouse. Each species may be present constantly
throughout the year, although in the northern part of the range there
is probably a slight withdrawal of the breeding birds in winter. The
individuals to be seen at that season, therefore, may not always be
the same as those observed during the summer. It is certain, however,
that these species do not regularly perform extensive journeys.
While the blue jay is disposed to be secretive, it is such a showy
and noisy bird that it is not likely to escape notice. In the
vicinity of Washington, D. C., as in many other places, it is present
the year round, but at the end of September or early in October
when the weather is becoming cooler, troops of jays are sometimes
seen working southward through the trees. A corresponding northward
movement occurs again in May. This is unquestionably a migration to
and from some winter range, but its extent or significance is not now
known. Some light is being shed on the matter, however, through the
records of banded birds, and these eventually will fill in a more
perfect picture of the movements of this species. One jay, banded on
September 14, 1923, at Waukegan, Ill., was killed at Peruque, Mo.,
on November 15 of the same year; another, banded at Winnetka, Ill.,
on June 16, 1925, was retaken at Sulphur Rock, Ark., the following
December 10; a third, banded on May 6, 1925, at Whitten, Iowa, was
recaptured at Decatur, Ark., on January 22, 1926. These three birds
unquestionably had made a flight that had every appearance of being a
true migration to winter quarters in Missouri and Arkansas.
The black-capped chickadee is apparently resident in many places, but
occasionally in winter it invades the range of the southern Carolina
chickadee, and in northern Canada it is regularly a migrant.
In the coastal plain between Washington, D. C., and the Atlantic
Ocean, the white-breasted nuthatch is usually absent during the
summer, nesting at that season in the higher, or piedmont, country.
Late in fall, however, it appears in fair abundance in the wooded
bottoms, remaining at the lower levels until the following March or
April.
Some birds, including the screech owl, bobwhite, Carolina wren,
and mockingbird, seem to be actually sedentary, but even these are
sometimes given to post-breeding wanderings. Ordinarily bobwhites
that are marked with numbered bands are seldom retaken far from the
area where banded, but sometimes they will travel 10 miles or more.
A screech owl banded at Glenwood, Minn., in March, was recovered
the following December at Emmetsburg, Iowa, 180 miles south. Such
flights, however, are probably more in the nature of a search for
new feeding areas, or to escape from a winged enemy, than a true
migratory journey.
=Migration of the white-throated sparrow=
The white-throated sparrow, one of the most abundant members of its
family, breeds from northern Mackenzie and the southern part of the
Ungava Peninsula south to southern Montana, northern Pennsylvania,
and Massachusetts. The winter range extends from the southern part
of the breeding range south to the Gulf coast and northeastern
Mexico. It is therefore a common migrant in many sections. Since it
is a ground-feeding bird and is readily attracted to the vicinity of
dwellings, it has been banded in large numbers, the total to November
14, 1949, being nearly 283,500. It would be expected that these would
yield a comparable number of return records that would furnish basic
data relative to the migrations of the species. Such, however, is
not the case. Banded white-throated sparrows are rarely recaptured
at stations between the breeding and wintering grounds. Operators of
stations in the winter area, as Thomasville, Ga., and Summerville,
S. C., have obtained return records showing that these birds do come
back to the exact winter quarters occupied in previous seasons. The
fact that they do not again visit banding stations on their migration
routes indicates some unusual aspects of their travels, which it is
hoped will eventually be discovered by banding studies. Problems
of this type constitute definite challenges to the student of bird
migration.
=Migration of the yellow-billed loon=
The semiannual movements of the yellow-billed loon present an unusual
problem in migration. It breeds along the Arctic coast, probably
from Cape Prince of Wales eastward to Franklin Bay, and also in the
interior of northern Canada south to Clinton-Colden, Aylmer, and
Artillery Lakes, where it is rather common. It has been reported
as already present by May 25 at the mouth of the Liard River, in
southwestern Mackenzie. This coincides with the time that first
arrivals are noted fully 700 miles north, at Point Barrow, Alaska.
The problem has been to ascertain the route used by these birds to
their principal nesting grounds in the interior.
For a long time it was believed that this big diver did not winter in
large numbers anywhere on the Pacific coast, and it had been supposed
that the spring route extended 2,000 miles northeastward from a
wintering ground somewhere in eastern Asia to Bering Strait, then 500
miles still northeast to round Point Barrow, then 500 miles east to
the coast of Mackenzie, and finally 700 miles south--in spring--to
the region near the eastern end of Great Slave Lake.
The yellow-billed loon is a powerful flier, and it is probable that
this suggested route is correct for those birds that breed in the
northern coastal regions. A reasonable doubt may be entertained,
however, whether the breeding birds of Great Slave Lake and
contiguous areas reach their breeding grounds by the 700-mile flight
south from the Arctic coast. Within recent years it has been found
that these birds are fairly common in the maze of channels and
islands off the coast of southeastern Alaska as late as the last of
October and in February. Possibly they are present there during the
period from November through January also, or they may at that time
move farther off shore and so escape detection. If this region is
an important wintering ground, as seems probable, then it is likely
that the breeding birds of the interior reach their nesting grounds
by a flight eastward across the mountains, a trip that is well within
their flying ability, rather than by a circuitous route around the
northern coast. The air-line distance from southeastern Alaska to the
mouth of the Liard River is in fact less than the distance to that
point from the mouth of the Mackenzie.
Differing routes to various parts of a large breeding or wintering
ground, and used by large groups of individuals of other species,
are not unknown. For example, the redhead duck is one of the common
breeding ducks of the Bear River marshes of Utah, where a great many
have been banded each summer. The recovery records of banded redheads
show that while many travel westward to California, others start
their fall migration in the opposite direction and, flying eastward
across the Rocky Mountains, either turn southeast across the plains
to the Gulf of Mexico, or deliberately proceed in a northeasterly
direction to join the flocks of this species moving toward the
Atlantic coast from the prairie regions of southern Canada.
_Conclusions_
The migration of birds as it is known today had its beginning in
times so remote that its origins have been entirely obscured, and
it can be interpreted now only in terms of present conditions. The
causes underlying migration are exceedingly complex. The mystery
that formerly cloaked the periodic travels of birds, however, has
been largely dispelled through the fairly complete information that
is now available concerning the extent and times of the seasonal
journeys of most of the species. Many gaps, however, still remain
in our knowledge of the subject. Much has been learned, and present
knowledge is being placed on record, but it must be left to future
study to clear away many of the uncertainties that continue to make
bird migration one of the most fascinating subjects in the science of
ornithology.
Each kind of bird seems to have its own reaction to its environment,
so that the character of movement differs widely in the various
species, and seldom do any two present the same picture. In
fact, bird migration has been described as a phase of geographic
distribution wherein there is a more or less regular seasonal
shifting of the avian population caused by the same factors that
determine the ranges of the sedentary species. If this view is
correct, then it must be recognized that the far-reaching works of
man in altering the natural condition of the earth's surface can so
change the environment necessary for the well-being of the birds as
to bring about changes in their yearly travels. The nature and extent
of the changes wrought by man on the North American Continent are
easily apparent. Forests have been extensively cut away and their
places have been taken by second growth or cultivated land, and wide
stretches of prairie and plain have been broken up, irrigated, and
devoted to agriculture. These great changes are exerting a profound
effect upon the native bird populations, and the various species may
be either benefited or adversely affected thereby.
The Federal Government has recognized its responsibility to the
migratory birds under changing conditions brought about by man, and
by enabling acts for carrying out treaty obligations, it is now
giving most species legal protection under regulations administered
by the Fish and Wildlife Service. Much is being done by legislation
for the welfare of the birds. The effectiveness of these conservation
laws, however, is increased in the same measure that the people of
the country become acquainted with the facts in the life histories of
the migrants and interest themselves personally in the well-being of
the various species. Long before the white man came to America the
birds had established their seasonal lanes of migration throughout
the Western Hemisphere. The economic, inspirational, and esthetic
values of these migratory species dictate that they be permitted
to continue their long-accustomed and still-mysterious habits of
migration from clime to clime.
Appendix I--_List of Birds Mentioned in the Text_
Common name Scientific name
American egret _Casmerodius albus egretta_
Arctic tern _Sterna paradisaea_
Atlantic brant _Branta bernicla hrota_
Atlantic golden plover _Pluvialis dominica dominica_
Bank swallow _Riparia riparia_
Barn swallow _Hirundo rustica erythrogaster_
Bartramian sandpiper or _Bartramia longicauda_
upland plover
Belted kingfisher _Ceryle alcyon_
Black-and-white warbler _Mniotilta varia_
Black-billed cuckoo _Coccyzus erythropthalmus_
Black brant _Branta bernicla nigricans_
Black-capped chickadee _Parus atricapillus atricapillus_
Black-crowned night heron _Nycticorax nycticorax hoactli_
Black duck _Anas rubripes_
Black-headed grosbeak _Pheucticus melanocephalus_
Blackpolled warbler _Dendroica striata_
Black-throated blue warbler _Dendroica caerulescens_
Bluebird _Sialia sialis_
Blue goose _Chen caerulescens_
Blue jay _Cyanocitta cristata_
Bluethroat _Cyanosylvia suecica_
Blue-winged teal _Anas discors_
Bobolink _Dolichonyx orizivorus_
Bobwhite _Colinus virginianus_
Bohemian [greater] waxwing _Bombycilla garrulus pallidiceps_
Brewer's blackbird _Euphagus cyanocephalus_
Broad-winged hawk _Bueto platypterus_
Bronzed grackle _Quiscalus guiscula versicolor_
Brown [tree] creeper _Certhia familiaris_
Cackling [Canada] goose _Branta canadensis minima_
California quail _Lophortyx californica_
Canada goose _Branta canadensis_
Canvasback _Aythya valisineria_
Cape May warbler _Dendroica tigrina_
Cardinal _Richmondena cardinalis_
Carolina chickadee _Parus carolinensis_
Carolina wren _Thryothorus ludovicianus_
Chimney swift _Chaetura pelagica_
Chipping sparrow _Spizella passerina_
Chuck-wills-widow _Caprimulgus carolinensis_
Clark's nutcracker _Nucifraga columbiana_
Cliff swallow _Petrochelidon pyrrhonota_
Common tern _Sterna hirundo_
Cooper's hawk _Accipiter cooperi_
Coot [American] _Fulica americana_
Cowbird _Molothrus ater_
Crossbill _Loxia curvirostra_
Crow _Corvus brachyrhynchos_
Duck hawk [peregrine falcon] _Falco peregrinus_
Eastern fox sparrow _Passerella iliaca iliaca_
Eider _Somateria mollissima_
Emperor goose _Philacte canagica_
Evening grosbeak _Hesperiphona vespertina_
European blackbird _Turdus merula merula_
Field sparrow _Spizella pusilla_
Forster's tern _Sterna forsteri_
Frigate [man-o'-war] bird _Fregata magnificens_
Golden-crowned kinglet _Regulus satrapa_
Golden plover _Pluvialis apricaria_
Golden-winged warbler _Vermivora chrysoptera_
Goshawk _Accipiter gentilis_
Grackle _Quiscalus quiscula_
Gray-cheeked thrush _Hylocichla minima_
Greenland wheatear _Oenanthe oenanthe leucorhoa_
Harris's sparrow _Zonotrichia querula_
Hermit thrush _Hylocichla guttata_
Herring gull _Larus argentatus_
Horned lark _Eremophila alpestris_
Horned owl _Bubo virginianus_
House finch _Carpodacus mexicanus_
Ipswich sparrow _Passerculus princeps_
Jacksnipe [see Wilson's snipe] _Capella gallinago delicata_
Junco _Junco hyemalis_
Kentucky warbler _Oporonis formosus_
Kingbird _Tyrannus tyrannus_
Knot _Calidris canutus_
Kodiak fox sparrow _Passerella iliaca hyperborea_
Lapland longspur _Calcarius lapponicus_
Lapwing _Vanellus vanellus_
Lesser yellowlegs _Totanus flavipes_
Little blue heron _Florida caerulea_
Loggerhead shrike _Lanius ludovicianus_
Long-billed marsh wren _Telmatodytes palustris_
Mallard _Anas platyrhynchos_
Maryland yellowthroat _Geothlypis trichas trichas_
Meadowlark _Sturnella magna_
Migratory quail _Coturnix coturnix_
Mockingbird _Mimus polyglottos_
Mourning dove _Zenaidura macroura_
Myrtle warbler _Dendroica coronata_
Nighthawk _Chordeilies minor_
Noddy tern _Amous stolidus_
Northern phalarope _Lobipes lobatus_
Northern robin _Turdus migratorius migratorius_
Orchard oriole _Icterus spurius_
Ovenbird _Seiurus aurocapillus_
Pacific [American] golden _Pluvialis dominica fulva_
plover
Parasitic jaeger _Stercorarius parasiticus_
Peregrine falcon [duck hawk] _Falco peregrinus_
Pine Grosbeak _Pinicola enucleator_
Pine warbler _Dendroica pinus_
Pintail _Anas acuta tzitzihoa_
Pipit _Anthus spinoletta_
Poor-will _Phalaenoptilus nuttallii_
Purple finch _Carpodacus purpureus_
Purple martin _Progne subis_
Purple sandpiper _Erolia maritima_
Raven _Corvus corax_
Red-eyed vireo _Vireo olivaceus_
Redhead _Aythya americana_
Red-legged kittiwake _Rissa brevirostris_
Redpoll _Acanthis flammea_
Redstart _Setophaga ruticilla_
Red-tailed hawk _Buteo jamaicensis_
Red-winged blackbird _Agelaius phoeniceus_
Robin _Turdus migratorius_
Rock wren _Salpinctes obsoletus_
Rose-breasted grosbeak _Pheucticus ludovicianus_
Ross's goose _Chen rossi_
Ross's gull _Rhodostethia rosea_
Rosy finch _Leucosticte tephrocotis_
Rough-legged hawk _Buteo lagopus_
Ruby-throated hummingbird _Archilochus colubris_
Ruffed grouse _Bonasa umbellus_
Rusty blackbird _Euphagus carolinus_
Sanderling _Crocethia alba_
Scarlet tanager _Piranga olivacea_
Scaup _Aythya marila_
Screech owl _Otus asio_
Sharp-shinned hawk _Accipiter striatus_
Shumagin fox sparrow _Passerella iliaca unalaschensis_
Slate-colored junco _Junco hyemalis_
Snow bunting _Plectrophenax nivalis_
Snow goose _Chen hyperborea_
Snowy heron _Leucophoyx thula_
Snowy owl _Nyctea scandiaca_
Song sparrow _Melospiza melodia_
Sooty fox sparrow _Passerella iliaca fuliginosa_
Sooty tern _Sterna fuscata_
Sora or Carolina rail _Porzana Carolina_
Southern robin _Turdus migratorius achrusterus_
Starling _Sturnus vulgaris_
Swainson's hawk _Buteo swainsoni_
Swamp sparrow _Melospiza georgiana_
Townsend's fox sparrow _Passerella iliaca townsendi_
Tree sparrow _Spizella arborea_
Tufted titmouse _Parus bicolor_
Turkey vulture _Cathartes aura_
Turnstone _Arenaria interpres_
Upland plover [Bartramian _Bartramia longicauda_
sandpiper]
Valdez fox sparrow _Passerella iliaca sinuosa_
Vesper sparrow _Pooecetes gramineus_
Western palm warbler _Dendroica palmarum palmarum_
Western tanager _Piranga ludoviciana_
Western wood pewee _Contopus richardsonii_
White-breasted nuthatch _Sitta carolinensis_
White-throated sparrow _Zonotrichia albicollis_
White-winged scoter _Melanitta fusca_
Widgeon _Mareca americana_
Williamson's sapsucker _Sphyrapicus thyroideus_
Wilson's [common] snipe _Capella gallinago delicata_
Winter wren _Troglodytes troglodytes_
Woodcock _Scolopax rusticola_
Wood thrush _Hylocichla mustelina_
Worm-eating warbler _Helmitheros vermivorus_
Wrentit _Chamaea fasciata_
Yakutat fox sparrow _Passerella iliaca annectens_
Yellow-billed cuckoo _Coccyzus americanus_
Yellow-billed loon _Gavia adamsii_
Yellow-headed blackbird _Xanthocephalus xanthocephalus_
Yellow palm warbler _Dendroica palmarum hypochrysea_
Yellow warbler _Dendroica petechia_
Appendix II--_Bird Banding_
Frequent reference has been made in this bulletin to bird banding
as a means for obtaining information on the migrations and life
histories of birds. Since 1920 this work in North America has been
under the direction of the Fish and Wildlife Service in cooperation
with the Dominion Wildlife Service of Canada. Each year birds to the
number of a quarter of a million or more may be marked with numbered
bands.
As anyone interested in birds, either game or nongame, may have a
marked individual come into his hands, there are several pertinent
details that should be remembered if the recovery record is to have
maximum value in advancing the science of ornithology.
1. The reporting letter should be addressed to: Bird Banding Office,
Patuxent Research Refuge, Fish and Wildlife Service, Laurel, Md.
2. In the letter print the full number of the band, including the
series designation and the serial number. The series designation may
be a single letter or a two- or three-digit number and may be stamped
to the left or over the serial number. The series designation, if
a number such as "48" or "50," is not a date and should not be
so interpreted. Full numbers are correctly written as: A-678901;
48-345920; 141-543678; 20-167; 496-00517; etc.
3. If the bird is alive and uninjured, read the number carefully
without removing the band, and release the bird. It may be reported
again. If it is dead, remove the band and, after flattening it out,
attach it to the letter with scotch tape or surgical adhesive tape.
Should it be desired as a souvenir, it will be returned upon request.
4. Give in the report the exact date, the location (town, county,
State, etc.) and the manner in which the bird was obtained, that is,
whether it was shot, found dead, trapped, etc.
5. Print your own name and permanent address clearly on the letter.
6. Keep a record of the band number and refer to it should there be
any subsequent correspondence about it with the Service. The number
is always the clue to any record of a banded bird.
Some bands may bear the inscription "Notify F. and Wildlife Service,
Washington, D. C." or "Notify Biological Survey, Washington, D. C.,"
and on the smaller sizes these may be abbreviated to "F. and W. Serv.
Wash. D. C." or "Biol. Surv. Wash. D. C."
All reports of the recovery of banded birds will be acknowledged with
the name of the bird, the date and place where it was banded, and the
name and address of the bander.
The banding of birds is done by regular officers of the United
States and Dominion Services, by biologists and technicians of the
States and Provinces, and by volunteer cooperators who are specially
licensed under the provisions of the Migratory Bird Treaty Act. The
banding of migratory waterfowl is largely restricted to Federal and
State officers and is done chiefly in refuge areas. Most nongame
birds are banded by volunteer cooperators who are scattered over the
United States, Canada, and Alaska. The bands are furnished without
charge by the Service but each station operator supplies his own
traps and other equipment.
To participate in this work, certain rules must be adhered to.
Applicants for banding permits:
1. Must be at least 18 years of age.
2. Must be thoroughly competent to identify positively all local
birds.
3. Must have their ability vouched for by three recognized
ornithologists or by other banders.
Application blanks for the Federal permits required may be obtained
from the Bird Banding Office, Patuxent Research Refuge, Fish and
Wildlife Service, Laurel, Md., or, in Canada, from the Chief,
Dominion Wildlife Service, Ottawa, Ontario.
_Bibliography_
Since almost every faunal paper on birds has a bearing on the subject
of migration, only a few can be listed in this publication. Those
included were selected to aid the student wishing to pursue the
subject further and to cover not only all cited in the text but also
others consulted and used in its preparation.
Allard, H. A.
1928. Bird migration from the point of view of light and length of
day changes. Am. Naturalist 62, pp. 385-408.
Austin, O. L., Jr.
1928. Migration-routes of the Arctic tern (_Sterna paradisaea_
Brunnich). Northeastern Bird Banding Assn. Bull., vol, 4, pp.
121-125.
Baird, S. F.
1866. The distribution and migration of North American birds. Am.
Jour. Sci., vol. 41, pp. 78-90, 184-192, 337-347.
Bergtold, W. H.
1926. Avian gonads and migration. The Condor, vol. 28, pp. 114-120.
Bissonette, Thomas Hume
1936. Normal progressive changes in the ovary of the starling
(_Sturnus vulgaris_) from December to April. The Auk, vol. 53,
pp. 31-50, illus.
1939. Sexual photoperiodicity in the blue jay (_Cyanocitta
cristata_). Wilson Bull., vol. 51, pp. 227-232, pis. 9-11.
Clark, Austin H.
1925. Animal flight. Sci. Monthly, vol. 20, pp. 5-20. Clarke, W. E.
1912. Studies in bird migration. 2 vol., illus. London. Cooke, May
Thacher
1937. Flight speed of birds. U. S. Dept. Agr. Cir. 428, 13 pp.
1945. Transoceanic recoveries of banded birds. Bird-Banding, vol.
16, No. 4, pp. 123-129.
Cooke, W. W.
1888. Report on bird migration in the Mississippi Valley in the
years 1884 and 1885. U. S. Dept. Agr., Div. Econ. Ornith. Bull.
2, 313 pp., illus.
1904. Distribution and migration of North American warblers. U. S.
Dept. Agr., Div. Biol. Survey Bull. 18, 142 pp.
1904. The effect of altitude on bird migration. The Auk, vol. 21,
pp. 338-341.
1905a. Routes of bird migration. The Auk, vol. 22, pp. 1-11.
1905b. The winter ranges of the warblers (_Mniotiltidae_). The Auk,
vol. 22, pp. 296-299.
1906. Distribution and migration of North American ducks, geese,
and swans. U. S. Dept. Agr., Bur. Biol. Survey Bull, 26, 90 pp.
1908. Averaging migration dates. The Auk, vol. 25, pp. 485-486.
1910. Distribution and migration of North American shore birds. U.
S. Dept. Agr., Bur. Biol. Survey Bull. 35, 100 pp., illus.
1913a. Distribution and migration of North American herons and
their allies. U. S. Dept. Agr., Bur. Biol. Survey Bull. 45, 70
pp., illus.
1913b. The relation of bird migration to the weather. The Auk, vol.
30, pp. 205-221, illus.
1914. Distribution and migration of North American rails and their
allies. U. S. Dept. Agr. Bull. 128, 50 pp. illus,
1915a. Bird migration. U. S. Dept. Agr. Bull. 185, 47 pp., illus.
1915b. Bird migration in the Mackenzie Valley. The Auk, vol. 32,
pp. 442-459, illus.
1915c. Distribution and migration of North American gulls and their
allies. U. S. Dept. Agr. Bull. 292, 70 pp., illus.
1915d. The yellow-billed loon: A problem in migration. The Condor,
vol. 17, pp. 213-214.
Coues, E.
1878. Birds of the Colorado Valley, a repository of scientific and
popular information concerning North American ornithology. U. S.
Dept. Interior Misc. Pub. II, 807 pp., illus.
DeLury, Ralph E.
1938. Sunspot Influences. Jour. Royal Astron. Soc. of Can., pt. 1,
March 1938, pt. 2, April 1938, 50 pp.
Dixon, Joseph
1916. Migration of the yellow-billed loon. The Auk, vol. 33, No. 4,
pp. 370-376.
Eaton, Richard Jefferson
1933-34. The migratory movements of certain colonies of herring
gulls. Bird-Banding, vol. 4, No. 4, pp. 165-176; vol. 5, No. 1,
pp. 1-19; vol. 5, No. 2, pp. 70-84.
Earner, Donald S.
1945. The return of robins to their birthplaces. Bird-Banding, vol.
16, No. 3, pp. 81-99.
Furlong, W. R.
1933. Land-birds in a gale at sea. Bird Lore, vol. 35, No. 5, pp.
263-265.
Gätke, H.
1895. Heligoland as an ornithological observatory, the results
of fifty years' experience. (Transl. from the German by R.
Rosenstock). 599 pp., illus. Edinburgh.
Gordon, Donald A.
1948. Some considerations of bird migration: continental drift and
bird migration. Science, vol. 108, pp. 705-711.
Griffin, Donald R.
1940. Homing experiments with Leach's petrels. The Auk, vol. 57,
No. 1, pp. 61-74.
1943. Homing experiments with herring gulls and common terns.
Bird-Banding, vol. 14, No. 1 and 2, pp. 7-33.
1944. The sensory basis of bird navigation. Quart. Rev. of Biol.,
vol. 19, No. 1, pp. 15-31.
Grinnell, J.
1931. Some angles in the problem of bird migration. The Auk, vol.
48, pp. 22-32.
Gross, A. O.
1927. The snowy owl migration of 1926-27. The Auk, vol. 44, pp.
479-493, illus.
1947. Cyclic invasions of the snowy owl and the migration of
1945-46. The Auk, vol. 64, No. 4, pp. 584-601.
Harrison, T. H.
1931. On the normal flight speeds of birds. Brit. Birds, vol. 25,
pp. 86-96. Jaeger, Edmund C.
1948. Does the poor-will "hibernate"? The Condor, vol. 50, p. 45.
1949. Further observations on the hibernation of the poor-will. The
Condor, vol. 51, pp. 105-109.
Lewis, Harrison F.
1937. Migrations of the American brant (_Branta bernicla hrota_).
The Auk, vol. 54, pp. 73-95.
Lincoln, F. C.
1917. Bohemian waxwing (_Bombycilla garrula_) in Colorado. The Auk,
vol. 34, p. 341.
1922. Trapping ducks for banding purposes: with an account of the
results obtained from one waterfowl station. The Auk, vol. 39,
pp. 322-334, illus.
1924a. Banding notes on the migration of the pintail. The Condor,
vol. 26, pp. 88-90.
1924b. Returns from banded birds, 1920 to 1923, U. S. Dept. Agr.
Bull.
1268, 56 pp., illus.
1926. The migration of the cackling goose. The Condor, vol. 28, pp.
153-157, illus.
1927a. Notes on the migration of young common terns. Northeastern
Bird Banding Assoc. Bull., vol. 3, pp. 23-28, illus.
1927b. Returns from banded birds, 1923 to 1926. U. S. Dept. Agr.
Tech. Bull. No. 32, 95 pp., illus.
1928. The migration of young North American herring gulls. The Auk,
vol. 45, pp. 49-59.
1934a. Distribution and migration of the redhead (_Nyroca
americana_). Trans. 20th Am. Game Conf., pp. 280-287, map.
1934b. The operation of homing instinct. Bird-Banding, vol. 5, No.
4, pp. 149-155.
1935a. Ancestral highways of the sky. American Forests, vol. 41,
No. 4, pp. 157, 159, and 196, 4 figs.
1935b. The migration of North American birds. U. S. Dept. Agr. Cir.
363, 72 pp., 29 figs., bibliog.
1935c. The waterfowl flyways of North America. U. S. Dept. Agr,
Cir. 342, 12 pp., illus.
1936. Trans-Atlantic flight of gull-billed tern. The Auk, vol. 53,
No. 3,
1937a. The enigma of bird migration. Sci. Digest, vol. 1. No. 5,
pp. 63-65.
1937b. Our greatest travelers. In "The Book of Birds," Nat. Geog.
Soc, vol. 2, pp. 301-350, 1937.
1939a. The migration of American birds. Doubleday, Doran & Co., New
York, pp. i-xii and 1-189, col. pl. i-xii, maps 1-22.
1939b. The individual vs. the species in migration studies. The
Auk, vol. 56, No. 3, pp. 250-254.
1940. When the dove travels. Outdoor Georgia, vol. 1. No. 4, pp. 9
and 22 (1 map).
1941. The waterfowl flyways. "Wild Ducks," Am. Wildlife Inst., pp.
20-29.
1942a. La migración de aves en el Hemisferio Occidental. Pub.
and dist. by Panam. Sec. of the Int. Comm. for the Protection
of Birds. Pp. 1-12, illus. (maps). Both Spanish and English
versions.
1942b. Migration routes and flyways. In "Ducks, Geese and Swans of
North America," by Francis H. Kortright, Am. Wildlife Inst., pp.
47-53.
1944a. Regulation by flyways. Am. Rifleman, vol. 92, No. 11, pp.
21-23, 26, illus. (3 maps).
1944b. Chimney swift winter range discovered. The Auk, vol. 61, No.
4, pp. 604-609, map.
1945a. The mourning dove as a game bird. Fish and Wildlife Serv.
Cir. 10, pp. 1-8, illus.
1945b. Flyway regulations. Trans. 10th N. A. Wildlife Conf., pp.
50-51.
1946. Keeping up with the waterfowl. Audubon Mag., vol. 48, No. 3,
pp. 194-205, 7 illus., 10 maps. Reprinted as Fish and Wildlife
Serv. Leaflet 294, April 1947, pp. 1-10.
1949. The Mississippi flyway. Lead-off chapter in "Wildfowling
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_Index_
Advantages of migration, 6
Aerial obstructions, 76
Altitudes of travel, 26
Ancestral home theory, 8
Arctic route, 68
Aristotle, 2, 4, 5
Atlantic coast route, 53
Atlantic oceanic route, 48
Baldpate, 62
Banding studies, 81, 92
Blackbird, 32, 33, 60
Brewer's, 32
European, 4
red-winged, 22, 32, 33, 35, 37
rusty, 70
yellow-headed, 32
Bluebird, 9, 34, 37, 81
Bluethroat, 19
Bobolink, 32, 55, 56 (map), 69, 70, 71
Bobwhite, 32, 34, 82, 83
Brant, 57, 58
Atlantic, 57
Black, 68
Bullbat, 32
Bunting, snow, 34
Canvasback, 58
Cardinal, 34, 82
Chickadee, 7, 72
black-capped, 83
Carolina, 83
Chuck-wills-widow, 55
Clarke, W. E., 4, 6
Compsothlypidae, 32
Conclusions, 85
Continental drift, theory of, 11
Coot, 55
Coues, Elliott, 4
Cowbird, 29
Crane, 2, 4, 6, 16, 26, 27, 28
Creeper, brown, 75
Crossbill, 7, 32, 74
Crow, 20, 22, 32
Clark's, 73
Cuckoo, black-billed, 55
yellow-billed, 55
Diurnal migration, 15
Diving birds, 16
Dove, 4
mourning, 19
turtle, 2, 6
Duck, 2, 15, 16, 19, 20, 21, 32, 33, 37, 42, 58, 60, 61, 62, 68
black, 20, 33, 58, 61
eider, 68
scaup, 58
sea, 59, 63
Eel, 29
Egret, 73
Eider, 68
Evolution of migration routes, 70
Exhaustion, 78
Falcon, peregrine, 19
Fall flights, 37
Finch, 43
house, 82
purple, 74
rosy, 72
Fishes, 29
Flicker, 70
Flight speed, 18
Flycatcher, 15, 19, 31
Fly ways, 46
Atlantic, 49 (map), 58
Mississippi, 50 (map)
Central, 51 (map)
Pacific, 52 (map)
Gätke, Heinrich, 19
Goose, 2, 4, 15, 16, 19, 20, 21, 33, 59, 60, 61, 62
blue, 22, 32, 61, 62
cackling, 63
Canada, 15, 21, 22 (map), 32, 58, 59, 81
emperor, 68
Ross's, 64 (map)
snow, 32, 72
Gordon, Donald A., 30
Goshawk, 12
Grackle, 37
bronzed, 32
Great Lakes route, 60
Grebe, 34
Grosbeak, 45, 74
black-headed, 37
evening, 74
pine, 72
rose-breasted, 33, 45, 46 (map)
Gross, Alfred O., 74
Groups, movements of, 12
Grouse, ruffed, 82
Gull, 16, 68, 73, 78
herring, 73
Ross's, 68
Hawk, 2, 16, 19, 26, 34, 42
broad-winged, 16
Cooper's, 16
duck, 19, 20
red-tailed, 16
rough-legged, 16
sharp-shinned, 16
Swainson's, 16
Herodotus, 2
Heron, 19, 20, 73
black-crowned night, 73
little blue, 73
snowy, 73
Hesiod, 2
Hesperornis, 11
Hibernation, 4
Homer, 2
Homing instinct, 30
Hummingbird, ruby-throated, 79
Ichthyornis, 11
Influence of weather, 80
Insects, 29
Jacksnipe, 37
Jaeger, Edmund C., 5
Jaeger, parasitic, 68
Jay, blue, 34, 83
Junco, 10, 34, 72
slate-colored, 37, 70, 75
Kingbird, 32, 42, 55
Kingfisher, belted, 34
Kinglet, 77
golden-crowned, 75
Kite, 4
Kittiwake, red-legged, 68
Knot, 11, 42
Lapwing, 28
Lark, horned, 19
meadow, 34, 76
Lewis, Harrison F., 57
Lincoln, Frederick C., 5
Long distance migrations, 38
Longspur, 34, 76
Lapland, 37, 75
Loon, 16
yellow-billed, 84, 85
Mackenzie Valley route, 60
Magnetic sense, 30
Magnus, Olaus, 4
Mallard, 22, 31, 33, 58
Man-o'-war bird, 30
Martin, purple, 12
Migration, advantages of, 6
altitudes, 26
distances, 38
diurnal, 15
fall, 37
historical accounts, 4
long distance, 38
mystery of, 4
nocturnal, 15
origin, 7
perils, 75
problems, 81
routes, 41
segregation during, 31
short, 34
species and groups, 12
speed, 18
theories of causes, 7
undetermined, 34
vagrant, 73
variable, 35
vertical, 72
weather, 80
Mississippi Valley route, 60
Mockingbird, 83
Movements of residents, 82
Movements of species and groups, 12
Murre, 29
Mystery of migration, 4
Nighthawk, 9, 16, 32, 38, 55, 60, 70
Nocturnal migration, 15
Northern ancestral home theory, 8
Nutcracker, Clark's, 73
Nuthatch, 7
white-breasted, 83
Orientation, 28
Origin of migration, 7
Oriole, 15
orchard, 9
Ovenbird, 70, 78, 80
Owl, great horned, 34
screech, 83
snowy, 12, 74
Pacific coast route, 63
Pacific oceanic route, 66
Passerella iliaca, 35
Pelican, 4, 16, 26
Perils, aerial obstructions, 76
exhaustion, 78
migration, 75
storms, 75
Pewee, western wood, 72
Phalarope, 33
northern, 27
Photoperiodism, theory of, 9
Pigeon, homing, 30, 31
Pintail, 22, 55, 62, 79
Pipit, 73
Pliny, 4
Plover, 15
golden, 11, 19, 48, 49, 51, 54 (map), 66, 68, 71, 79
upland, 15
Poor-will, 5
Problems, migration, 81
banding studies, 81
migration of the white-throated sparrow, 84
migration of the yellow-billed loon, 84
movements of residents, 82
Quail, 2, 34
California, 82
migratory, 2
Rail, 4, 15
Carolina, 79
Raven, 19
Redhead, 58, 62, 85
Redpoll, 12
Redstart, 14, 45, 47 (map), 70, 78
Residents, movements of, 82
Robin, 9, 22, 24, 33, 34, 35, 61, 70, 76
Routes, 41, 53 (map)
Arctic, 68
Atlantic coast, 53
Atlantic oceanic, 48
"bobolink," 55, 56 (map)
evolution of, 70
flyways, 46
Great Lakes, 60
Great Plains, 62
Mackenzie Valley, 60
Mississippi Valley, 60
narrow, 42
Pacific coast, 63
Pacific oceanic, 66
Rocky Mountain, 62
wide, 42
Rowan, William, 10
Salmon, 29
Sanderling, 11, 27
Sandpiper, 15, 27
Bartramian, 15
purple, 42
Sapsucker, Williamson's, 72
Scaup, 58
Scoter, 63
white-winged, 59, 65
Segregation, 31
Shore bird, 9, 11, 12, 32, 33, 38, 42, 48, 50, 55, 57, 60, 61
Short and undetermined migrations, 34
Shrike, 19, 34
loggerhead, 37
Snipe, 15
Wilson's, 37
Snowbird, 10
Sora, 79
Southern ancestral home theory, 8
Sparrow, 15, 31, 32, 34, 60, 76, 77
chipping, 37, 70
field, 37
fox, 35, 36 (map)
Harris's, 43 (map), 44, 45
Ipswich, 43
song, 33, 34
swamp, 75
tree, 34, 37, 75
vesper, 37
white-throated, 75, 84
Species, movements of, 12
Speed, flight, 18
migration, 18
Starling, 4
Stork, 2, 4, 6, 27
Storms, 75
Swallow, 2, 4, 6, 9, 17, 18, 26, 32, 34, 57
bank, 55
barn, 20, 38, 60
cliff, 16, 17 (map), 26, 38
hibernating, 4
Swan, 4
Swift, 4, 16, 19, 20, 34
chimney, 4, 32
Tanager, 55, 66
scarlet, 33, 44 (map), 45
western, 65 (map), 66, 67 (map)
Teal, blue-winged, 20, 55, 58, 60
Tern, arctic, 11, 38, 39 (map), 40, 41, 68
common, 40
Forster's, 40
noddy, 30
sooty, 30
Theories of migration, 7
Thrush, 4, 15, 19, 21, 27, 31, 38, 60, 77
gray-cheeked, 21, 23 (map), 55
hermit, 75
wood, 55
Titlark, 73
Titmouse, 34
tufted, 82
Transmutation, 5
Turd us migratorius, 35
Turnstone, 11
Turtle [dove], 2, 6
Vagrant migration, 73
Variable migrations within species, 35
Vertical migration, 72
Vireo, 15, 55, 75, 77
red-eyed, 69 (map), 70
Vulture, 26
turkey, 34
Warbler, 15, 17, 18, 27, 60, 75, 76
black and white, 12, 13 (map), 14 (map)
blackpolled, 16, 18, 24, 25 (map), 55, 60, 70
black-throated blue, 14
Cape May, 37
golden-winged, 63
Kentucky, 63
myrtle, 61, 70
palm, 37
pine, 37
summer, 21
wood, 31, 32
worm-eating, 63
yellow, 14, 21, 70
Waterfowl, 20, 47, 55, 58, 59, 61, 64,93
Waxwing, 32, 33
Bohemian, 12, 74
Weather, influence of, 80
Wheatear, Greenland, 11
Widgeon, 55
American, 62
Woodcock, 37
Woodpecker, 34
Wren, 15
Carolina, 34, 82, 83
long-billed marsh, 33
rock, 37
winter, 34, 75
Wrentit, 82
Yeagley, Henry L., 30
Yellowlegs, lesser, 21
Yellowthroat, Maryland, 35, 78
* * * * *
Transcriber Note
Illustrations moved to prevent splitting paragraphs. Minor typos
corrected.
*** End of this LibraryBlog Digital Book "USFWS Circular 16: Migration of Birds (1950)" ***
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