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Title: Occurrence of the Garter Snake, Thamnophis sirtalis, in the Great Plains and Rocky Mountains
Author: Fitch, Henry S., 1909-2009, Maslin, T. Paul
Language: English
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Copyright Status: Not copyrighted in the United States. If you live elsewhere check the laws of your country before downloading this ebook. See comments about copyright issues at end of book.

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[Transcriber's Note: Original spelling and punctuation have been
retained.  In particular, both Eutainia and Eutaenia are used in
the original, as are both pickeringi and pickeringii.]



  UNIVERSITY OF KANSAS PUBLICATIONS
  MUSEUM OF NATURAL HISTORY

  VOLUME 13, NO. 5, PP. 289-308, 4 FIGS.
  FEBRUARY 10, 1961



        OCCURRENCE OF THE GARTER SNAKE,
        THAMNOPHIS SIRTALIS,
        IN THE GREAT PLAINS AND ROCKY MOUNTAINS

                       BY

        HENRY S. FITCH AND T. PAUL MASLIN



  UNIVERSITY OF KANSAS
  LAWRENCE
  1961
  UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

  EDITORS: E. RAYMOND HALL, CHAIRMAN, HENRY S. FITCH,
  ROBERT W. WILSON

  VOLUME 13, NO. 5, PP. 289-308, 4 FIGS.
  PUBLISHED FEBRUARY 10, 1961

  UNIVERSITY OF KANSAS
  LAWRENCE, KANSAS

  PRINTED IN
  THE STATE PRINTING PLANT
  TOPEKA, KANSAS
  1961



  OCCURRENCE OF THE GARTER SNAKE, THAMNOPHIS SIRTALIS, IN THE GREAT
                     PLAINS AND ROCKY MOUNTAINS

                               BY

                 HENRY S. FITCH AND T. PAUL MASLIN


INTRODUCTION

The common garter snake (_Thamnophis sirtalis_) has by far the most
extensive geographic range of any North American reptile, covering
most of the continental United States from the Atlantic to the Pacific
and from south of the Mexican boundary far north into Canada and
southeastern Alaska. Of the several recognized subspecies, the eastern
_T. s. sirtalis_ has the most extensive range, but that of _T. s.
parietalis_ in the region between the Mississippi River and the
Rocky Mountains is almost as large. The more western _T. s. fitchi_
occurring from the Oregon and California coasts east through the
northern Great Basin, has the third largest range, while the far
western subspecies _pickeringi_, _concinnus_, _infernalis_ and
_tetrataenia_, and the Texan _T. s. annectens_ all have relatively
small ranges.

Since the publication of Ruthven's revision of the genus _Thamnophis_
more than 50 years ago, little attention has been devoted to the study
of this widespread and variable species, except in the Pacific Coast
states (Van Denburgh, 1918; Fitch, 1941; Fox, 1951). However, Brown
(1950) described the new subspecies _annectens_ in eastern Texas,
and many local studies have helped to clarify the distribution of the
species in the eastern part of the continent and to define the zone of
intergradation between the subspecies _sirtalis_ and _parietalis_. In
our study attention has been focused upon _parietalis_ in an
attempt to determine its western limits and its relationships to the
subspecies that replace it farther west.


TAXONOMIC HISTORY

_Thamnophis sirtalis parietalis_ Say was described (as _Coluber
parietalis_) in 1823 from a specimen obtained in what is now
Washington County, Nebraska, on the west side of the Missouri River
three miles upstream from the mouth of Boyer's River [Iowa], or
approximately eight miles north of Omaha. Although the type locality
was unequivocally stated in the original description, Nebraska was not
mentioned since the state was not yet in existence. Because the mouth
of Boyer's River, the landmark by means of which the type locality is
defined, is in Iowa, the impression has been imparted that the type
locality itself is in Iowa (Schmidt, 1953:175), and to our knowledge
the type locality has never been associated with Nebraska in the
literature.

Like all the more western subspecies, _parietalis_ is strikingly
different from typical _sirtalis_ in having conspicuous red markings.
The relationship between the two was early recognized. Several of
the other subspecies were originally described as distinct species.
_Coluber infernalis_ Blainville, 1835; _Tropidonotus concinnus_
Hallowell, 1852; _Eutainia pickeringi_ Baird and Girard, 1853; and
others now considered synonyms eventually came to be recognized
as conspecific with _Thamnophis sirtalis_. Ruthven (1908:166-173)
allocated all western _sirtalis_ to either _parietalis_ or
_concinnus_, the latter including the populations of the northwest
coast in Oregon, Washington and British Columbia.

Subsequent more detailed studies by later workers with more abundant
material led to the recognition of some subspecies that Ruthven
thought invalid and led to the resurrection of some names that he
had placed in synonomy. Van Denburgh and Slevin (1918:198) recognized
_infernalis_ as the subspecies occurring over most of California and
southern Oregon, differing from more northern populations in having
more numerous ventrals and caudals and a paler ground color. Fitch
(1941:575) revived the name _pickeringii_ for a melanistic population
of western Washington and southwestern British Columbia, restricting
the name _concinnus_ to a red-headed and melanistic population of
northwestern Oregon, and restricting the name _infernalis_ to a
pale-colored population in the coastal strip of California.

These changes left most of the populations formerly included in
_concinnus_ and _infernalis_ without a name, and Fitch (_op. cit._)
revived _Thamnophis sirtalis tetrataenia_ (Cope) to apply to
them. However, Fox (1951:257) demonstrated that the type of _T. s.
tetrataenia_ came from the San Francisco peninsula (rather than
from "Pit River, California" as erroneously stated in the original
description) and that the name was applicable to a localized
peninsular population rather than to the wide-ranging far western
subspecies, which he named _T. s. fitchi_. The range of _fitchi_
includes California west of the Colorado and Mohave deserts
(except for the narrow strip of coast occupied by _infernalis_ and
_tetrataenia_), Oregon except the northwestern part, Washington east
of the Cascade Range, most of British Columbia, extreme southeastern
Alaska (occurring farther north than any other terrestrial reptile of
North America) and parts of Idaho.

Neither Fox (1951) nor Fitch (1941) defined the eastern limits of
_fitchi_ or discussed its relationship to the subspecies _parietalis_.
Wright and Wright (1957:849) stated: "Fitch ... did not even mention
the big scrap basket form _parietalis_, from which he pulled _T. s.
fitchi_ (old _tetrataenia_). That comparison remains to be made, and
the east boundary of _fitchi_ and the west boundary of _parietalis_
are still nebulous." We have undertaken to define better than has been
done before the ranges of _parietalis_ and _fitchi_ and to list
the diagnostic characters separating these two subspecies. Freshly
collected material of both has been compared. At the time of his 1941
revision the senior author had never seen a live or recently preserved
specimen of _parietalis_.


DISCONTINUITY OF RANGE

Wherever it occurs at all, the common garter snake is usually
abundant. Because of its diurnal habits and the concentration of its
populations along watercourses, it is not likely to be overlooked.
There are few, if any, remaining large areas in the United States
where herpetologists have not carried on field work. It may be
anticipated that certain rare and secretive species will still be
found far from any known stations of occurrence, and seeming gaps in
the ranges of these species will eventually be filled. But for the
common garter snake the negative evidence provided by the lack of
records from extensive areas should be taken into account in mapping
the range.

Most large collections of garter snakes contain misidentified
specimens. The diagnostic differences in color and pattern are often
obscured, especially if the specimens are poorly preserved. Many
specimens deviate from the scalation typical of the form they
represent, and key out to other species. Isolated records should
therefore be accepted with caution. A case in point is Colorado
University Museum No. 46, from Buford, Rio Blanco County, Colorado,
originally identified by Cockerell (1910:131) as _Thamnophis sirtalis
parietalis_. This specimen, and another, now lost, from Meeker in the
same county seemingly served as the basis for mapping the range of
_sirtalis_ across the western half of Colorado, for there seem to
be no other records from this part of the state. However, a
re-examination of the specimen from Buford shows it to be an atypical
individual of another species, _T. elegans vagrans_. A specimen of
_T. radix haydeni_ (Col. U. Mus. No. 3165) was the basis for Maslin's
(1959:53) record of _parietalis_ in Baca County on the north fork
of the Cimarron River in southeastern Colorado. Brown (1950:203) has
mentioned the difficulty of defining the range of _sirtalis_ in the
southern Great Plains because of misidentifications of the similar _T.
radix_.

The range of the common garter snake has never been adequately mapped
in the Rocky Mountain and Great Basin states. Recent general works
(Smith, 1956:291; Wright and Wright 1957:834; Stebbins 1954:505;
Conant 1958:328) which have shown maps of the over-all range of
_sirtalis_, differ sharply as to the extent of its distribution
in Texas, New Mexico and Arizona, but all show its distribution as
continuous over the more northern Great Basin and Rocky Mountain
states. However, specimens and specific locality records from
this extensive area seem to be scarce and some are based on early
collections of doubtful provenance. Throughout this region the low
rainfall, fluctuating and uncertain water supply, and general lack of
mesic vegetation along many of the streams render the habitat rather
hostile to garter snakes in general. _Thamnophis elegans vagrans_,
highly adapted to conditions in this region and generally distributed
over it, doubtless offers intensive competition to the species
_sirtalis_ wherever they overlap and perhaps constitutes a limiting
factor for _sirtalis_ in some drainage basins.

Convincing records of _sirtalis_ are lacking from all of
Colorado--except for those in the drainage basins of the South Platte,
and the Río Grande east of the Continental Divide--from the eastern
half of Utah (east of the Wasatch Range), from New Mexico except for
the Río Grande drainage (with one record each for the Canadian and
Pecos river drainages), from southwestern Wyoming (at least that
part in the Colorado River drainage basin), from the western half of
Oklahoma, and from Texas, except the eastern and extreme western and
northern parts. The species occurs in Nevada only near that state's
western and northern boundaries. The range is therefore much different
than it has been depicted heretofore, with the populations living east
of the Continental Divide widely separated from those to the west
for the entire length of the Rocky Mountains south of the Yellowstone
National Park region. The populations of northern Utah, southern
Idaho, and Nevada, which have been considered _parietalis_ are thus
far removed from the main population of that subspecies to the east
and are isolated from them by the barrier of the Continental Divide
and arid regions farther west.

Although some of the records published for _Thamnophis sirtalis_ are
erroneous, being based on misidentifications of other species, various
outlying records, including those in western Kansas, the Panhandle of
Texas, and southeastern New Mexico probably represent localized relict
populations that have survived from a time when the species was more
generally distributed in this region. The population of _T. sirtalis_
in the Río Grande drainage of New Mexico is geographically isolated
and remote from other populations of the species. Except for a few
isolated and highly localized populations the species is absent from
the Republican, Smoky Hill, Arkansas, Cimarron, Canadian, Red, Brazos,
Colorado and Pecos rivers and their tributaries west of the one
hundredth meridian in the arid High Plains.

Streams in this region of High Plains are in most instances unsuitable
habitats because they are in eroded channels, have a variable
and uncertain water supply, and have poorly developed riparian
communities. The marsh and wet meadow habitat preferred by _sirtalis_
in most parts of its range is almost absent. _T. radix_ and _T.
marcianus_, well adapted to conditions in this region, perhaps provide
competition that is limiting to _T. sirtalis_. However, several
well-isolated populations of _sirtalis_ have survived as relicts in
the southern Great Plains, presumably from a time several thousand
years ago when mesic conditions were more prevalent, perhaps in an
early postglacial stage.

       *       *       *       *       *

Illustration: FIG. 1. Map of a part of the United States in
the region of the Great Plains and Rocky Mountains, and adjacent
northwestern Mexico showing supposed range (shaded) and localities of
authenticated occurrence (dots) of _Thamnophis sirtalis_. 1. _T.
s. fitchi_, 2. _T. s. parietalis_, 3. _T. s. annectens_, 4. _T. s.
ornata_. Records from Idaho and Wyoming are based on specimens in
the University of Kansas Museum of Natural History collection. Other
records are based on Woodbury (1931) for Utah, Hudson (1942) for
Nebraska, Maslin (1959) for Colorado, Smith (1956) for Kansas, R. G.
Webb (MS) for Oklahoma, Brown (1950) and Fouquette and Lindsay (1955)
for Texas, Cope (1900), Van Denburgh (1924), Little and Keller (1937)
for New Mexico, and Smith and Taylor (1945) for Mexico.

       *       *       *       *       *

Smith (1956:292) recorded _parietalis_ from three outlying stations
in the western quarter of Kansas, from Wallace, Hamilton and Meade
counties in the drainages of the Smoky Hill River, Arkansas River, and
Cimarron River, respectively. Permanent springs in Meade County State
Park perhaps account for the survival of an isolated colony there.
Several specimens from that locality seen by Fitch in August, 1960,
when recently collected by a University of Michigan field party,
seemed to be of the Texas subspecies _annectens_, as their dorsal
stripes were reddish orange, and markings on the dorsolateral area
were pale yellow rather than red. Specimens from the Texas Panhandle,
from Hemphill County (Brown, 1950:207) and nine miles east of Stinnet,
Hutchison County (Fouquette and Lindsay, 1955:417) likewise are most
nearly like _annectens_ judging from the authors' descriptions. The
specimens from nine miles east of Stinnet averaged large; the two
largest would have attained or slightly exceeded four feet in length
if they had had complete tails. No _sirtalis_ so long as four feet has
been recorded elsewhere.

Records are lacking from the drainages of the Republican, North
Canadian, Brazos and Colorado River drainages in the High Plains, but
possibly isolated populations occur in some of these also. The only
record from the Pecos River drainage is that of Bundy (1951:314) from
Wade's Swamp near Artesia, Eddy County, New Mexico. This locality
is separated by some 140 miles from any other known station of
occurrence.

From extreme southern Colorado south across New Mexico to the Mexican
border _T. sirtalis_ occurs in continuous or nearly continuous
populations in the Río Grande Valley, and has been recorded from many
localities. It has been recorded from relatively few localities of
tributary streams (Los Pinos, Abiqui, Santa Fe) all near the main
valley. There is one record from the Ocate River, a headwaters
tributary of the Canadian River, in the Sangre de Cristo
Mountains near other localities in the Río Grande drainage. The
southwestern-most known locality of occurrence is Casas Grandes in the
Mexican state of Chihuahua some 130 miles southwest of El Paso, Texas,
and near the Continental Divide. The Río Casas Grandes must have once
been a tributary of the Río Grande, but now its desert drainage basin
is isolated.


RE-DESCRIPTION OF A SUBSPECIES FROM NEW MEXICO

Most specimens of a population of _sirtalis_ occurring in New Mexico
are recognizably different from most specimens of other populations.
This New Mexican population is therefore here recognized as a distinct
subspecies:

THAMNOPHIS SIRTALIS ORNATA Baird

  _Eutaenia ornata_ Baird, 1859:16.
  _Eutaenia sirtalis dorsalis_ Cope, 1900:1076.
  _Thamnophis sirtalis parietalis_ (part) Van Denburgh, 1924:222.

    _Type._--U. S. Nat. Mus. No. 960, obtained at El Paso, Texas,
    at some time in the eighteen fifties by Col. J. D. Graham.

    _Range._--Río Grande and vicinity, from Conejos and Costilla
    counties in extreme south-central Colorado south across New
    Mexico to Mexican border. Records from neighboring drainage
    systems, Casas Grandes in Chihuahua and Artesia and Ocate
    River in New Mexico, probably also pertain to _ornata_.

    _Description._--A specimen in the University of New Mexico
    Natural History Museum (E. D. Flaherty No. 560, obtained
    one mile west and one-half mile south of Isleta, Bernalillo
    County, New Mexico, on May 31, 1959) was described as
    follows while its colors were still but little altered by
    preservatives: Top of head olive, supralabials pale gray,
    edged with black posteriorly; chin milky white, with dark
    edges posteriorly on fifth, sixth and seventh infralabials;
    dorsal stripe yellow; including middorsal row of scales and
    little more than adjacent half of row on either side of it;
    dorsolateral area olive-brown with row of black spots on its
    lower half, these spots elliptical, averaging about size
    of one scale on anterior part of body, smaller posteriorly;
    adjacent spots separated by interspaces of approximately
    their own length, irregular black markings on upper half
    of dorsolateral area not forming definite spots but fused
    longitudinally to form continuous black border to dorsal
    stripe; crescent-shaped red markings in areas between scale
    rows three to nine, these markings invading edges of scales,
    and themselves having ill-defined edges blending into the
    darker ground color; lateral stripe pale, yellowish gray,
    limited to scale rows two and three for most of its length,
    but including rows four and five in neck region; row of
    irregular black marks low on each side, with each mark
    centering on anterior part of lower half of scale of first
    row but overlapping onto corners of adjacent ventrals;
    approximately every other scale of first row so marked;
    ventral surface pale, suffused with bluish tint; most of
    ventrals marked on anterior edges with pair of semicircular
    black spots, each situated about two-thirds of distance from
    mid-line to lateral edge of ventral; these marks diminishing
    in size and finally disappearing on posterior part of body;
    ventral surface otherwise immaculate.

    Lepidosis normal for genus and species, with preoculars single
    on each side, supralabials 7-7, infralabials 8-8, ventrals
    159, anal entire, subcaudals 77 (including terminal spine),
    paired except for second, third and fourth; scale rows 19
    from neck slightly beyond mid-body, fifth on left side ending
    opposite 86th ventral; length from snout to vent 670 mm., tail
    202 mm.

    _Comparisons._--From _T. s. parietalis_, _T. s. ornata_
    differs in its consistently pale ground color, olive instead
    of dark brown or black. In respect to color-pattern _ornata_
    stands in approximately the same relation to _parietalis_ as,
    farther west, _T. s. infernalis_, a pale subspecies of the
    California coast, stands in relation to _T. s. fitchi_.
    Nevertheless, _fitchi_ consistently has a dark ground color,
    whereas _parietalis_ is highly variable, and the color of an
    occasional specimen (for example KU 17032 from Douglas County,
    Kansas) matches _ornata_ in olive coloration. These unusually
    pale specimens of _parietalis_ differ from _ornata_ in not
    having a continuous black edge along each side of dorsal
    stripe; black pigment of this area is concentrated into rows
    of spots alternating with those of lower series. From _T. s.
    infernalis_, _ornata_ differs in having paired black spots
    on the ventrals and in having more than three series of red
    crescents on dorsolateral area of each side.

_Remarks._--The type of _ornata_ seems to have been lost, and the
available information concerning it is far from satisfactory. In the
original description, Baird listed three specimens, purportedly from
"Indianola, Texas" (J. H. Clark, 438), from the Río Grande, Texas (J.
H. Clark, 768), and from near San Antonio, Texas (Dr. Kennerley, no
number). None of these three specimens could have been _ornata_ as
conceived of by us because all were collected outside the geographic
range of _ornata_. However, there was also included a plate with a
drawing of a specimen and a reference to an earlier paper (Baird and
Girard, 1853) in which a specimen obtained by Col. Graham "Between
San Antonio and El Paso" was described. Smith and Brown (1946:72) have
presented evidence that this specimen figured (rather than any of the
three specifically mentioned) served as a basis for the plate, and
they therefore considered it to be the holotype of _ornata_, even
though Baird referred this specimen to "_Eutaenia parietalis_ Say" in
the same paper (1859) in which the original description of _ornata_
was published. Cope (1900:1079) listed under _Eutaenia sirtalis
parietalis_ a specimen, U. S. Nat. Mus. No. 960, from El Paso,
obtained by Col. Graham, and referred to it as a type (without
specifying of what it was the type). Smith and Brown (_loc. cit._)
interpreted this statement by Cope as further evidence that the
specimen in question should be considered the type of _ornata_, and
they restricted the type locality, originally stated as "between San
Antonio and El Paso" to "El Paso." Actually all valid records of the
species _sirtalis_ from the vicinity of the Río Grande are from the El
Paso region or from farther north.

It is with some misgivings that we herewith accept the interpretation
proposed by Smith and Brown regarding the applicability of the name
_ornata_ and the designation by these authors of the now missing
specimen from the region of El Paso as the holotype of that form. The
evidence linking the name _ornata_ with the New Mexican subspecies is
tenuous; there is some doubt as to the provenance of U. S. Nat. Mus.
No. 960 (the supposed type), and even more doubt as to whether this
is the specimen depicted in the plate that formed part of the original
description.

Cope (1900:1076) recognized as a distinct subspecies, _Eutaenia
sirtalis dorsalis_, the same population that we recognize herein as
_T. s. ornata_, and Smith (1942:98) considered the name _dorsalis_ to
be a synonym of _T. s. parietalis_. However, it is almost certain
that both authors misapplied the name, since the type of Baird's
and Girard's (1853:31) _Eutainia dorsalis_ was obtained in Coahuila,
Mexico, between Monclova and the Río Grande, far south of the known
range limits of _T. sirtalis_ in Texas. The description does not fit
_T. sirtalis_ and almost certainly pertains to another species.

    _Specimens examined._--Univ. of Kansas Mus. Nat. Hist.
    (hereafter abbreviated to "KU") Nos. 5479 to 5497, from the
    north end of Elephant Butte Reservoir, Sierra County, New
    Mexico, and 8592 and 8593 from near Las Lunas, Valencia
    County, New Mexico; Univ. of New Mexico Mus. Nos. 571 and
    572 (J. S. Findley) from 2 miles west and 1/4 mile north of
    Albuquerque, Bernalillo County, New Mexico, and No. 4021 (E.
    D. Flaherty) from 1 mile west and 1/2 mile south of Isleta,
    Bernalillo County, New Mexico.


DESCRIPTION OF _T. S. PARIETALIS_

From most of the vast area occupied by _parietalis_, material has
not been available to us, and our concept of this subspecies is based
chiefly on specimens and living material from Kansas and northeastern
Colorado. A total of 520 live _parietalis_ has been examined from the
University of Kansas Natural History Reservation some 130 miles south
and a little east of the type locality in Nebraska. These probably
differ but little from typical specimens. The range of individual
variation in pattern is especially notable. In those from the
Reservation, the ground color varies from dull olive-brown to almost
jet black. The markings on the dorsolateral area vary in color, in
shade and in extent. These marks are chiefly confined to the skin
between the scales of rows three to nine. Although most typically
these marks are of some shade of red (hence the name "red-sided garter
snake"), they may be pale buff, or pale greenish yellow, or may even
have a bluish tint. In approximately ten per cent of the specimens
from the Reservation there is no red at all in the pattern, which
hence is similar to that of _T. s. sirtalis_ in the eastern United
States. Only a minority have all the dorsolateral marks red, and
in some of these specimens the marks higher on the sides are
progressively paler red, having a bleached out appearance. Most
typically the marks between rows three to six are some shade of red
while the smaller marks between rows six to nine are pale--yellowish,
greenish, or buffy. In some the pale area of the lateral stripe is in
varying degrees suffused with red, which may extend onto the edges of
the ventrals and even to the underside of the tail.

_T. s. parietalis_ may be diagnosed, on the basis of these snakes from
northeastern Kansas, as follows: Size medium large (length 23.5 to
34.5, or, exceptionally 43.5 inches in adult males; 32.5 to 46.0
inches in adult females), dorsolateral color olive to black.
Approximately every other scale of the third row is bordered above and
anteriorly by a crescent-shaped area of scarlet colored skin. Similar
crescent-shaped areas border the scales of the fourth and fifth rows
and often two adjacent crescents meet at the ends of an intervening
scale and fuse forming an H-shaped mark. Placed alternately with these
markings are similar but smaller crescent-shaped markings on the skin
of the upper half of the dorsolateral area on each side bordering
every other scale of the sixth, seventh and eighth rows. The crescents
of this upper series also may fuse to form series of H-shaped markings
alternating with those of the lower series. The dorsal stripe is
yellow with a faint dusky suffusion; it involves all of the middorsal
scale row and approximately the adjacent half of the row on either
side. The lateral stripe is faint, yellowish gray, chiefly on the
upper half of the second scale row, lower half of third, and the
intervening skin, and is often invaded or suffused by the red marks
of the dorsolateral area. The first scale row, adjacent corners of
the ventrals, and lower half of the second scale row are suffused
with dark pigment and appear dusky, but this area is often marked with
black, setting off the paler area of the lateral stripe. The ventrals
are dull, whitish, faintly suffused with yellowish, greenish or
bluish, each ventral having a black dot usually of semicircular shape
on its anterior margin near the anterolateral corner.


COMPARISON OF _T. S. PARIETALIS_ AND _T. S. FITCHI_

Like most widely ranging subspecies, _parietalis_ and _fitchi_ vary
geographically and local populations often are noticeably different
from typical material. It is possible that future revisors will
recognize additional subspecies, but in the variant populations
known to us the degree of differentiation is slight as compared,
for instance, with that in the subspecies of _Thamnophis elegans_.
Scalation is remarkably uniform in all the subspecies of _sirtalis_,
but coastal and northern populations tend to have fewer ventrals
and subcaudals than do their counterparts farther inland and farther
south. In their geographic variation the ventrals and subcaudals
follow clines, and do not in themselves warrant subspecific divisions.
Variation occurs chiefly in the color and pattern including the
intensity of dark pigmentation of the dorsolateral area, head, ventral
surface and lower edge of the lateral stripe; in extent, position and
shade of red or pale colored markings on the dorsolateral area; in
presence and extent of reddish suffusion on the head, in the region
of the lateral stripe, and on the ventral surface of the tail. Most
of these same characters vary within the subspecies _fitchi_, but the
range of variation is relatively minor. Fitch (_op. cit._:582-584)
described typical populations and also described briefly several small
series from British Columbia, Idaho, Oregon, and California which were
not entirely typical. Most frequent variation was in heavy reddish
suffusion on the sides of the head not found in typical _fitchi_. In
each local population of this subspecies the characters seem to be
remarkably uniform and stable.

       *       *       *       *       *

Illustration: FIG. 2. Diagrammatic drawing of pattern in stretched
skin of _T. s. fitchi_; the pale markings on the black dorsolateral
area are scarlet (× 2-1/2).

       *       *       *       *       *

Illustration: FIG. 3. Diagrammatic drawing of stretched skin of
_T. s. parietalis_; the scarlet markings extend farther dorsally
than in _T. s. fitchi_ and black spots are prominent on the ventrals
laterally. Some individuals of _parietalis_ have much paler ground
color, resembling _ornata_ except in minor details (× 2-1/2).

       *       *       *       *       *

Illustration: FIG. 4. Diagrammatic drawing of stretched skin of
_T. s. ornata_. The ground color is like that of _parietalis_ but
paler with a continuous black area bordering the dorsal stripe (×
2-1/2).

       *       *       *       *       *

_T. s. parietalis_ differs from _fitchi_ in several trenchant
characters, and there are additional slight or average differences
between the two. In approximate order of their importance the
differences are as follows: 1) The red (or pale yellow or green or
buffy) marks on skin between the scales on the upper half of the
dorsolateral area (that is between the sixth and seventh, seventh and
eighth and eighth and ninth scale rows) present in _parietalis_ are
missing in _fitchi_ or are represented by only an occasional small
fleck. 2) The dorsolateral area is black or nearly so in _fitchi_ but
averages paler in _parietalis_, in which a wide range of shades may be
found from black to olive brown. 3) The red of the dorsolateral area
frequently invades the lateral stripe, which sometimes is mostly red,
and may even invade the ventrals in _parietalis_, but in _fitchi_ the
red marks are usually confined to the dorsolateral area, and do not
invade the lateral stripe. 4) The prominent paired black dots
or semicircular marks on the anterior edge of each ventral in
_parietalis_ are largely lacking in _fitchi_, which rarely has any
dark marks on the ventral surface. 5) The dorsal stripe consistently
involves the middorsal scale row and the adjacent half of the next row
on each side, and is bright yellow in _fitchi_, but in _parietalis_
it may be slightly wider, may be duller with more dusky suffusion, and
its edges may be less sharply defined.


INTERMEDIATE AND ATYPICAL POPULATIONS

Of many specimens examined from eastern Oregon, Idaho, Utah, Wyoming
and Colorado, few were typical of either _parietalis_ or _fitchi_.
Many were intermediate in some respects or showed a composite
of characters of the two subspecies. No well-defined belt of
intergradation exists, but the transition extends over more than a
thousand miles, with local populations somewhat isolated and slightly
differentiated along divergent lines. In view of this situation
some plausibility could be claimed for any of several dividing lines
between the subspecies. However, by far the most logical division
is the Continental Divide; south of the Teton Range it constitutes
a broad barrier separating eastern and western populations. Across
Montana and Canada also it constitutes a more or less formidable
barrier, with high altitudes and cold climates that probably are
limiting to garter snakes. With few exceptions the snakes from east of
the Continental Divide are more nearly like _parietalis_ in the sum of
their characters whereas those from west of the Divide are more nearly
like _fitchi_.

In the Teton Range and in Yellowstone National Park these garter
snakes occur in headwater streams up to the Continental Divide.
KU 27956 from Two Ocean Lake 3-1/2 miles northeast of Moran, Teton
County, Wyoming, agrees in its characters with _fitchi_, having the
red lateral marks small and inconspicuous, discernible only on the
anterior half of the body. The dorsolateral area is dark, almost
black. The ventrals lack dark markings.

In Utah, populations of _sirtalis_ occur in the drainages of the Bear,
Weber and Sevier rivers and other smaller streams of the western
half of the state. Obviously the species invaded Utah from the north,
probably at a time when Lake Bonneville, the predecessor of the
present Great Salt Lake, drained into the Snake River of Idaho.
Van Denburgh and Slevin (1918:190) separated from their western
"_concinnus_" and "_infernalis_" and allocated to _parietalis_ the
populations of Utah and southeastern Idaho, but presumably these
authors were not familiar with typical _parietalis_ of the Mid-west.
Subsequent authors (Wright and Wright, 1957:834; Stebbins, 1954:505;
Conant, 1958:328) have followed this arrangement. A re-examination of
specimens from Utah, including living individuals collected at Bear
Lake in the summer of 1959, indicates that they should be assigned to
_fitchi_ rather than to _parietalis_.

Likewise various specimens from the drainage basin of the Snake River
in Idaho are predominantly _fitchi_ in the sum of their characters,
although they differ from that subspecies in its most typical form and
resemble _parietalis_ in some respects. KU 23133 from two miles east
of Notus, Canyon County, Idaho, has the red crescents on the lower
part of the sides (between scale rows six and seven) consistently
developed on the anterior half of the body. KU 21873, a large female
from Bannock County, Idaho, is exceptional in having small lateral
black spots on the ventrals, resembling _parietalis_ most closely in
this respect. Also, it has the red lateral crescents unusually well
developed; the first three series are conspicuous, those of the fourth
series are consistently developed, and those of the fifth series show
occasionally.

Forty-five specimens in the University of Colorado Museum from
northwestern Colorado were subjected to pattern analysis. In three
specimens the dorsolateral black area between the dorsal stripe and
the lateral stripe on each side has no markings, and in eight others
there is only an occasional fleck or crescent on the skin between the
sixth and seventh scale rows. All others have the normal complement of
dorsolateral crescents or flecks between the scales of rows three and
four, four and five, and five and six. But, these specimens vary
in extent of development of the crescents in the upper half of the
dorsolateral area on each side--between scale rows six and seven,
seven and eight, and eight and nine. Only six snakes show traces of
the crescents of the uppermost series (between scale rows eight and
nine). Development of these crescents is variable but in all the
specimens the crescents are confined to the anterior half of the body.
The crescents between rows six and seven and between seven and eight
are present in 20 specimens and in ten of these the crescents are
conspicuous and regularly arranged, often meeting and consequently
form H-shaped markings. In most of the snakes the crescents are best
developed in the second fifth of the body and disappear posteriorly.
In five of the twenty, crescents between rows six and seven are fairly
regular, but those between rows seven and eight are few and appear
only sporadically. In eight specimens there are no crescents between
either rows seven and eight or eight and nine. In eight others the
crescents between rows six and seven are likewise absent, and only the
crescents between rows three to six are present.

These specimens from Colorado also differ from typical _parietalis_ in
having the black spots on the anterolateral edges of the ventrals less
developed. In three of the 45 these spots are lacking entirely and in
four others they are few and small. In the majority of specimens the
spots are from 1/4 to 1/5 the length of the ventrals. In approximately
one-third of the specimens the spots are absent posterior to mid-body.
In five specimens obtained at Sheridan Lake, Pennington County, South
Dakota, in the Black Hills in August, 1960, dorsolateral areas are
dark with red crescents small and inconspicuous, and with black spots
either lacking from the ventrals or only faintly developed. In two
specimens from Sundance, Crook County, northeastern Wyoming, the red
crescents are small and inconspicuous also. In one of these specimens,
KU 28028, small black spots are present in the corners of the
ventrals, but in the other, KU 23654, the spots are absent.

In having the dorsolateral area consistently black, with the three
uppermost series of red crescents reduced or absent, and in having the
ventral black spots reduced or absent, these specimens from Colorado,
Wyoming, and South Dakota differ from more eastern and more typical
_parietalis_, and tend toward _fitchi_, even more strongly than some
Idaho specimens tend toward _parietalis_. Nevertheless, all things
considered, the Continental Divide is the most logical boundary
between the two subspecies, even though occasional individuals and
even local populations deviate from the general trend of characters
from east to west.


ACKNOWLEDGMENTS

    Dr. Doris M. Cochran of the United States National Museum
    kindly furnished information concerning the type specimen of
    _Eutainia dorsalis_ formerly in the National Museum collection
    but now lost. Dr. James S. Findley of the University of New
    Mexico and Dr. Ralph J. Raitt of New Mexico State University
    contributed habitat notes and records of specimens and loaned
    us critical specimens of _T. sirtalis_ from New Mexico. Drs.
    George F. Baxter of the University of Wyoming, John M. Legler
    of the University of Utah, and Wilmer W. Tanner of Brigham
    Young University kindly provided us with information
    concerning the specimens in the collections of their
    respective institutions, and their personal observations
    concerning the distribution of garter snakes in their states.
    Alice V. Fitch, Chester W. Fitch and Donald S. Fitch assisted
    in the collection of fresh specimens in Oregon and Utah and
    the unsuccessful search of many a mosquito-infested meadow in
    southern Wyoming and northwestern Colorado in July, 1959. Dr.
    R. G. Webb made available his MS on reptiles of Oklahoma.

    This taxonomic study of garter snakes originated as a
    by-product of the senior author's study of ecology and
    economic bearing of snakes in the central Plains Region of the
    United States, for which support received from the National
    Science Foundation is gratefully acknowledged.


LITERATURE CITED

BAIRD, S. F.

    1859. Reptiles of the boundary. United States and Mexican
    Bound. Surv., 2, 1-35, 41 pls.

BAIRD, S. F., and GIRARD, C.

    1853. Catalogue of North American reptiles in the Museum of
    the Smithsonian Institution. Smithson. Miscl. Col., part 1,
    Serpents., pp. xvi + 172.

BROWN, B. C.

    1950. An annotated check list of the reptiles and amphibians
    of Texas. Baylor Univ. Studies, pp. xii + 259.

BUNDY, R. E.

    1951. New locality records of reptiles in New Mexico. Copeia,
    1951 (4):314.

COCKERELL, T. D. A.

    1910. Zoology of Colorado. Univ. of Colorado, Boulder, vii +
    262 pp.

CONANT, R.

    1958. A field guide to the reptiles and amphibians of the
    United States and Canada east of the 100th Meridian. Houghton
    Mifflin Co., Boston, xviii + 366 pp.

COPE, E. D.

    1900. The crocodilians, lizards and snakes of North America.
    Rept. U. S. Nat. Mus. for 1898, pp. 153-1270.

FITCH, H. S.

    1941. Geographic variation in garter snakes of the species
    _Thamnophis sirtalis_ in the Pacific Coast region of North
    America. Amer. Midland Nat., 26:570-592.

FOX, W.

    1951. The status of the gartersnake, _Thamnophis sirtalis
    tetrataenia_. Copeia, 1951:257-267.

FOUQUETTE, M. J., and LINDSAY, H. L., JR.

    1955. An ecological survey of reptiles in parts of
    northwestern Texas. Texas Jour. Sci., 7(4):402-421.

HUDSON, G. E.

    1942. The amphibians and reptiles of Nebraska. Nebraska
    Conserv. Bull. No. 24, pp. 1-146.

LITTLE, E. L., JR., and KELLER, J. G.

    1937. Amphibians and reptiles from the Jornada Experimental
    Range, New Mexico. Copeia, 1937 (4):402-421.

MASLIN, T. P.

    1959. An annotated check list of the amphibians and reptiles
    of Colorado. Univ. Colorado Studies, Ser. Biol. No. 6, 98 pp.

RUTHVEN, A. G.

    1908. Variations and genetic relationships of the
    garter-snakes. Bull. U. S. Nat. Mus., 61:xii + 201 pp.

SCHMIDT, K. P.

    1953. A check list of North American amphibians and reptiles.
    Univ. Chicago Press, vii + 280 pp.

SMITH, H. M.

    1942. The synonymy of the garter snakes (_Thamnophis_), with
    notes on Mexican and Central American species. Zoologica,
    27(17):97-123.

    1956. Handbook of amphibians and reptiles of Kansas (2nd ed.).
    Univ. Kansas Mus. Nat. Hist. Misc. Publ. No. 9, 356 pp.

SMITH, H. M., and BROWN, B. B.

    1946. The identity of certain specific names in _Thamnophis_.
    Herpetologica, 3:71-72.

SMITH, H. M., and TAYLOR, E. H.

    1945. An annotated check list and key to the snakes of Mexico.
    Bull. U. S. Nat. Mus., 187, 239 pp.

STEBBINS, R. C.

    1954. Amphibians and reptiles of western North America.
    McGraw-Hill Book Co., Inc., xxiv + 528 pp.

VAN DENBURGH, J.

    1924. Notes on the herpetology of New Mexico, with a list of
    the species known from the state. Proc. California Acad. Sci.,
    4th ser., 13(12):189-250.

VAN DENBURGH, J., and SLEVIN, J.

    1918. The garter-snakes of Western North America. Proc.
    California Acad. Sci., 4th ser., 8:181-270.

WOODBURY, A. M.

    1931. A descriptive catalog of the reptiles of Utah. Univ.
    Utah Biol. Ser., 1(4):1-129.

WRIGHT, A. H., and WRIGHT, A. A.

    1957. Handbook of snakes of the United States and Canada.
    Comstock Publ. Associates, Cornell Univ. Press, vol. 2, pp. i
    + ix and 565-1106.

_Transmitted November 8, 1960._





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