Taxonomy of the Chipmunks, Eutamias quadrivittatus and Eutamias umbrinus Part 1

Taxonomy of the Chipmunks, Eutamias quadrivittatus and Eutamias umbrinus.

by John A. White.

The differences in anatomy and color between many species of chipmunks are subtle, and refined techniques are required to discover them.

When "measuring" chipmunks taxonomically, it is necessary to use a "chipmunk scale" and not, for example, a "pocket-gopher scale." In explanation, some species of pocket gophers closely allied to each other, and even some subspecies of the same species, differ markedly in color and in size and shape of parts of the skeleton; comparable differences are not so p.r.o.nounced among many species of chipmunks.

HISTORICAL SUMMARY

Merriam (1905) was the first to show clearly that _Eutamias quadrivittatus_ is a distinct species, and pointed out that _E.

amoenus operarius_ (= _E. minimus operarius_) is a small species which resembles, and is found in some areas together with, _E.

quadrivittatus_.

Howell (1929) placed under _E. quadrivittatus_ the following subspecies: _E. q. quadrivittatus_, _E. q. hopiensis_, _E. q.

inyoensis_, _E. q. frater_, _E. q. sequoiensis_, and _E. q.

speciosus_.

Hardy (1945) placed _E. adsitus_ under _E. quadrivittatus_ as _E. q.

adsitus_, and Kelson (1951) placed _E. umbrinus_ under _E.

quadrivittatus_ as _E. q. umbrinus_.

Johnson (1943) re-established _E. speciosus_ as a separate species, and in California left only _E. q. inyoensis_ in _E. quadrivittatus_.

Thus, since 1943 the recognized subspecies of _E. quadrivittatus_ have been: _E. q. quadrivittatus_, _E. q. hopiensis_, _E. q. inyoensis_, _E. q. nevadensis_, _E. q. umbrinus_, and _E. q. adsitus_.

METHODS, MATERIALS, AND ACKNOWLEDGMENTS

Capitalized color terms, which are used in descriptions and comparisons, are of Ridgway, "Color Standards and Color Nomenclature," Washington, D. C., 1912.

In the synonymy of each subspecies there appears only the first usage of a name, second the first usage of the name combination now employed unless a new combination is proposed by me, and third pure synonyms. The last is recognizable as such because the type locality is appended to each.

Unless otherwise specified, all specimens are in the Museum of Natural History, University of Kansas. The various collections of inst.i.tutions and of private persons are indicated by the following symbols:

AM--American Museum of Natural History.

BS--United States Biological Surveys Collection.

CM--Colorado Museum of Natural History.

DC--Collection of Donald R. d.i.c.key (now the collection of the University of California at Los Angeles).

FC--Collection of James S. Findley.

KU--Museum of Natural History, University of Kansas.

MM--Museum of Zoology, University of Michigan.

NM--United States National Museum.

UU--Museum of Zoology, University of Utah.

WC--Collection of Edward R. Warren, Colorado College.

Of the external measurements, only the total length and the length of the tail are recorded in table 1. Some field collectors measured the ear from the notch and others from the crown; most collectors measured the length of the hind foot to the nearest millimeter rather than in tenths of a millimeter, as would have been desired. Consequently, I decided against using the lengths of the ear and hind foot in the study here reported on.

The measurements of the skull were made as shown in figure 1.

[Ill.u.s.tration: FIG. 1. Dorsal view of skull and a lateral and a medial view of the right lower jaw to show points between which measurements of the skull were taken. 1-3/4. Based on _Eutamias ruficaudus ruficaudus_, from 6 mi. S St. Mary, 6500 ft., Glacier Co., Montana. A to A'--greatest length of skull; B to B'--length of nasals; C to C'--zygomatic breadth; D to D'--least interorbital constriction; E to E'--cranial breadth; F to F'--inner mandibular length; G to G'--condylo-alveolar length of mandible.]

A total number of 434 specimens are listed as examined in this study, and additionally, numerous other specimens were superficially examined in the United States Biological Surveys Collection. Bacula of each of the named kinds of chipmunks in this paper, were examined.

Whenever two or more samples are stated to be significantly different, the meaning is that the difference is statistically significant.

The geographic distribution of each subspecies and the localities of specimens or series of specimens are plotted on the map (fig. 2).

When comparisons were made to ascertain specific and subspecific differences, only adults, or animals in which the enamel was worn through on the permanent P4 and p4 were used.

Within this age range, only specimens in comparable pelage were used to ascertain differences in color.

Miss Viola S. Schantz of the United States Fish and Wildlife Service, Mr. Alfred Bailey of the Colorado Museum of Natural History, Dr. W. H. Burt of the Museum of Zoology of the University of Michigan, Dr. Stephen D. Durrant of the Museum of Zoology of the University of Utah, Dr. Robert M. Stabler, curator of the Warren Collection of Colorado College, and Mr.

James S. Findley, generously loaned specimens for my use.

Doctors E. Raymond Hall, Rollin H. Baker, Robert W. Wilson, Keith R. Kelson, E. Lendell c.o.c.krum, and other friends and a.s.sociates have given valued suggestions and a.s.sistance. My wife, Alice M. White, made the ill.u.s.trations and helped me record and a.n.a.lyze the data.

a.s.sistance with field work is acknowledged from the Kansas University Endowment a.s.sociation, the National Science Foundation, and the United States Navy, Office of Naval Research, through contract No. NR161 791.

ACCOUNTS OF SPECIES AND SUBSPECIES

=Eutamias quadrivittatus= (Say)

_Diagnosis._--Size medium; general tone of upper parts tawny; cranial breadth averaging between 16.0 and 16.8 mm.; baculum distinguishable from that of any other species by the combination of width of base less than 1/4 of length of shaft, shaft having a maximum diameter of more than 1/4 mm., and height of keel 1/4 of length of tip.

=Eutamias quadrivittatus quadrivittatus= (Say)

_Sciurus quadrivittatus_ Say, in Jones, Long's Expedition to Rocky Mountains, 2:45, 1823.

_Eutamias quadrivittatus_, Miller and Rehn, Proc.

Boston Soc. Nat. Hist., 30:43, December 27, 1901.

_Tamias quadrivittatus gracilis_ J. A. Allen, Bull.

Amer. Mus. Nat. Hist., 3:99, June 1890, Type from San Pedro, Santa Fe Co., New Mexico.

_Eutamias quadrivittatus animosus_ Warren, Proc.

Biol. Soc. Washington, 22:105, June 25, 1909. Type from Irwin Ranch, Las Animas County, Colorado.

_Type._--None designated; from along Arkansas River, about 26 mi. below Canon City, Fremont County, Colorado; obtained on July 18, 1820.

_Diagnosis._--Size medium; dorsal dark stripes blackish; sides Cinnamon to Clay Color; crown Light Drab; baculum large.

_Description._--_Color pattern_: Head Cinnamon, shaded on crown to Light Drab; ocular stripe Fuscous Black, with Cinnamon along margins; other facial stripes Fuscous mixed with Cinnamon; ears Fuscous Black, Ochraceous-Tawny on anterior margin, grayish white on posterior margin and on postauricular patch; dark dorsal stripes black with Ochraceous-Tawny along margins; outer pair of dark stripes often mainly Tawny; light dorsal stripes grayish white, outer pair usually creamy white; sides Ochraceous-Tawny, shaded in the region of the shoulder with Cinnamon; rump and thighs Cinnamon-Buff mixed with Smoke Gray; antipalmar surfaces of forefeet Cinnamon-Buff; antiplantar surfaces of hind feet Pinkish Buff; dorsal surface of tail Fuscous Black, overlaid with Pinkish Buff; ventral surface of tail Ochraceous-Tawny, Fuscous Black along margin, Pinkish Buff along outermost edge; underparts creamy white. _Skull_: Large; braincase well inflated; zygomatic arches strong and slightly appressed to skull. _Baculum_: Large; long and slender.

_Comparisons._--From _E. q. hopiensis_, the only other subspecies in this species, _E. q. quadrivittatus_ differs in: Dorsal dark stripes blackish; crown grayer; rump and thighs grayer; general tone of upper parts darker.

_Remarks._--Specimens from the Chuska Mountains, Zuni Mountains, and Blanco, New Mexico, are intergrades between _E. q. quadrivittatus_ and _E. q. hopiensis_, but are referable to _E. q. quadrivittatus_.

In north-central Colorado _E. umbrinus_ occurs in the spruce and pine forests at higher alt.i.tudes, while to the south and east of this area _E. q. quadrivittatus_ occurs in growths of pinon in lower, semiarid areas. In the northern half of New Mexico and in south-central Colorado, _E. q. quadrivittatus_ occurs not only in semiarid habitats but also in the moist habitats of the forests of higher alt.i.tudes.