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 a.s.sociated 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 sc.r.a.p 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 antic.i.p.ated 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 c.o.c.kerell (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 compet.i.tion to the species _sirtalis_ wherever they overlap and perhaps const.i.tutes 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 Rio Grande east of the Continental Divide--from the eastern half of Utah (east of the Wasatch Range), from New Mexico except for the Rio 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 Rio 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.
marcia.n.u.s_, well adapted to conditions in this region, perhaps provide compet.i.tion 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.
Ill.u.s.tration: 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 Rio 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 Rio 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 Rio Casas Grandes must have once been a tributary of the Rio 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._--Rio 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, supral.a.b.i.als pale gray, edged with black posteriorly; chin milky white, with dark edges posteriorly on fifth, sixth and seventh infral.a.b.i.als; 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 inters.p.a.ces 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, supral.a.b.i.als 7-7, infral.a.b.i.als 8-8, ventrals 159, a.n.a.l 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 Rio 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 Rio 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 Rio 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 b.u.t.te 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.