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Geographic Distribution and Taxonomy of the Chipmunks of Wyoming online

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Geographic Distribution and Taxonomy
of the Chipmunks of Wyoming


By

JOHN A. WHITE



University of Kansas Publications

Museum of Natural History

Volume 5, No. 34, pp. 583-610, 3 figures in text

December 1, 1953



University of Kansas
LAWRENCE
1953



UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

Editors: E. Raymond Hall, Chairman, A. Byron Leonard, and Robert W.
Wilson

Volume 5, No. 34, pp. 583-610, 3 figures in text

December 1, 1953


UNIVERSITY OF KANSAS
Lawrence, Kansas


PRINTED BY
FERD VOILAND, JR., STATE PRINTER
TOPEKA, KANSAS
1953




CONTENTS


PAGE

Purpose 586

Methods, Materials, and Acknowledgments 586

Variation 587
Juveniles 587
Young 587
Subadults 588
Adults 588
Old adults 588

Key to the Species of Chipmunks Inhabiting Wyoming 589

Accounts of Species and Subspecies 590
_Eutamias minimus_ 590
_E. m. minimus_ 591
_E. m. consobrinus_ 593
_E. m. pallidus_ 594
_E. m. confinis_ 596
_E. m. silvaticus_ 597
_E. m. operarius_ 598

_Eutamias amoenus_ 602
_E. a. luteiventris_ 602

_Eutamias dorsalis_ 603
_E. d. utahensis_ 604

_Eutamias umbrinus_ 606
_E. u. umbrinus_ 606
_E. u. fremonti_ 607
_E. u. montanus_ 608

Review and Conclusions 609

Literature Cited 610


FIGURES

Figure 1. Subspecies of _Eutamias minimus_ 590

Figure 2. _Eutamias amoenus_ and _Eutamias dorsalis_ 604

Figure 3. Subspecies of _Eutamias umbrinus_ 605




PURPOSE

The purpose of the following account is to: (1) Show what kinds of
chipmunks occur in Wyoming; (2) point out the interrelationships
between these kinds; and (3) account, where possible, for the present
distribution of these animals in Wyoming.


METHODS, MATERIALS, AND ACKNOWLEDGMENTS

Capitalized color terms in the following accounts are of Ridgway,
"Color Standards and Color Nomenclature," Washington, D.C., 1912.

The measurements of the skull that were used in this study were
made as shown in White (1953:566, fig. 1). These are: Greatest
length of skull, zygomatic breadth, cranial breadth, length of
nasals, length of lower tooth-row, condylo-alveolar length of
mandible, and inner mandibular length.

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 hindfoot to the nearest millimeter
rather than in tenths of a millimeter as would have been desirable.
Consequently, I decided against using the length of the ear and
hindfoot in this report.

When the word "significantly" is used in comparisons, it is meant
to show that there is a significant statistical difference between
two or more samples. Whenever eight or more specimens from one
locality were available, the mean, range, standard deviation,
standard error of the mean, and coefficient of variability were
calculated.

Only adult specimens were used in comparison. "Aging" of specimens
is discussed on page 587 of this paper.

The geographic range of each species and subspecies is not
described in writing, for, the localities are plotted on maps along
with the geographic range of each subspecies, and under "specimens
examined" the locality of each specimen or series of specimens is
listed.

In the synonymy of each subspecies there appears, first the first
usage of a name, second the first usage of the name combination now
employed, and third, pure synonyms.

A total of 757 specimens of chipmunks are listed as examined in the
course of preparing this report. Additional specimens were less
carefully examined in the Biological Surveys Collection in
Washington, D.C. Specimens used in my study, unless otherwise
specified, are in the Museum of Natural History, University of
Kansas. The symbols representing the collections containing
specimens studied are as follows:

BS - United States Biological Surveys Collection.
FC - Collection of James S. Findley.
MM - Museum of Zoology, University of Michigan.
NM - United States National Museum.
KU - Museum of Natural History, University of Kansas.

I am grateful to Professor E. Raymond Hall for guidance in my study
and thank Doctors Robert W. Wilson, E. Lendell Cockrum, Keith R.
Kelson, A. Byron Leonard, Rollin H. Baker, and others at the Museum
of Natural History and Department of Zoology, University of Kansas,
for encouragement and advice. My wife, Alice M. White, made the
illustrations and helped me in many ways.

For permission to borrow and to study specimens, I thank Dr. W. H.
Burt of the Museum of Zoology, University of Michigan, Miss Viola
S. Schantz of the United States Fish and Wildlife Service, Mr.
Colin C. Sanborn of the Chicago Natural History Museum, and Mr.
James S. Findley.

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


VARIATION

Secondary sexual variation in chipmunks is small; the females are
slightly larger than the males. This difference in size is so slight
that it can be ignored when making taxonomic comparisons, for, large
samples of males and females of like age and from the same locality
were compared and were found statistically not to be significantly
different. This is in agreement with Johnson (1943:70) and Hall
(1946:329).

Variations of taxonomic worth are treated in the accounts of species
and subspecies.

Individual variation is slight, for, the analyses of measurements of
the skulls of series of specimens of like age, reveal markedly low
coefficients of variability resembling those published by Larrison
(1949).

The age-categories here recognized are based primarily on the structure
of the skull.

_Juveniles._ - Nasals proportionally shorter and more pointed anteriorly
than in other categories; zygomatic arches more appressed to cranium;
suture separating basisphenoid and presphenoid noticeably "open";
deciduous P4 and p4 show no wear through enamel; M3 and m3 not yet
erupted; peglike deciduous P3 strongly leaning posteriorly; molars show
no wear through enamel; parietals paperlike or thin; skull convex
dorsally; 1 to 1-1/2 months of age.

_Young._ - Nasals of adult proportions; zygomatic arches still
noticeably appressed anteriorly to cranium; suture between basisphenoid
and presphenoid still "open"; nasals rounded, no longer so pointed as
in juveniles; deciduous P4 and p4 show wear through enamel layer, and
in some specimens, permanent P4 and p4 can be seen beneath; roots of
deciduous P4 and p4 clearly show erosion beneath; M3 and m3 fully
erupted; peglike deciduous P3 still present; parietals noticeably
thicker and less paperlike; skull flattened (not so convex dorsally),
but not so flattened as in adults; 1-1/2 to 4 months of age.

In both juveniles and young the P4 and p4 are deciduous and differ in
occlusal pattern from the permanent P4 and p4. In the deciduous P4 the
anterior cingulum is projected strongly anteriorly forming the apex of
the sharpest angle of a triangle, whereas the permanent P4 is
trapezoidal in occlusal pattern. In the deciduous p4 the protoconid and
metaconid are close together giving this tooth a triangular appearance
in occlusal pattern, whereas this pattern in permanent p4 is
trapezoidal (see Hall 1926:390).

_Subadults._ - Adult configuration of skull reached; suture between
basisphenoid and presphenoid completely closed; nasals rounded
anteriorly; permanent P4 and p4 show no wear through enamel layer; wear
through enamel layer of molars noticeable, especially through
protocones; peglike permanent P3 slanting only slightly posteriorly;
skull only slightly convex dorsally; parietals solid and resistant to
pressure; lambdoidal crest weakly developed; 4 to 10 months of age.

_Adults._ - Lambdoidal crest well developed; supraorbital ridges
pronounced; P4 and p4 show wear through enamel layer and frequently as
worn as molars; noticeable wear on lophs and lophids of molars;
occlusal pattern always visible; ten months to 2 years of age.

_Old adults._ - Ridges and crests extremely well developed; occlusal
pattern of molariform teeth obliterated or nearly so; P3 noticeably
worn; 2 to 4 years or older.

The hypohyal and ceratohyal bones of the hyoid apparatus are distinct
from one another in juveniles and young, but are fused in subadults,
adults, and old adults.

Lack of suitable material prevented me from studying chipmunks younger
than juveniles. The patterns of growth of these younger chipmunks
probably closely follow the changes described by Hall (1926) for
_Citellus beecheyi_.

The tip of the baculum in juveniles and young is proportionally longer,
in relation to the shaft, than in subadults, adults, and old adults.

Juvenal (juveniles and young) pelage in chipmunks is characterized by
silkiness and sparseness, especially on the venter. The coloration of
this juvenal pelage resembles that of adults in winter pelage which is
duller than adult summer pelage. Adult pelage (subadults, adults, and
old adults) is not so silky as juvenal pelage, but there are more
hairs, especially on the venter. The color pattern is the same in both
juvenal and adult pelages.

Chipmunks are born naked and blind and in about two weeks the "body is
covered with silken hair clearly demonstrating the color pattern so
characteristic of chipmunks...." (Shaw 1944:282). This "silken hair" is
replaced by adult summer pelage, and juvenal chipmunks which are
molting into adult summer pelage closely resemble the adult males, and
later on in the summer, the adult females. Adult females molt later, as
a rule, than adult males probably because of lactation. Summer molt
begins, on chipmunks in Wyoming and South Dakota, in the latter part of
June and is completed by the latter part of August or the first part of
September.

Summer molt begins, topographically, in the region of the head and
progresses posteriorly to the base of the tail, for, the tail does not
molt into summer pelage. The winter molt starts at the same time at the
tip of the tail and at the base of the tail, and from each place
proceeds anteriorly. The sequence described above is the rule;
exceptionally, there are some specimens which molted in patches. In
most skins, molts are easily detected because distinct molt-lines were
formed. The above description of molting is based on study of a large
series of specimens of _Eutamias minimus silvaticus_ taken in several
seasons of the year.

The summer pelage is bright, more especially on the sides. In late
summer the pelage on the tail is markedly worn, and the hairs around
its outer margin are broken. In texture, the summer pelage is not so
soft as winter pelage, and this is probably owing to the presence of
large amounts of "kinky" underfur in the winter pelage.

The winter pelage is soft, dull in color, and gives the specimen a
grayish or an umbrous appearance. The guard hairs are longer than in
the summer pelage.


KEY TO THE SPECIES OF THE CHIPMUNKS OF WYOMING

1. Dorsal stripes faint; general tone of upper parts grayish.
_Eutamias dorsalis_, p. 603

1'. Dorsal stripes distinct; general tone of upper parts tawny (not
grayish).

2. Venter yellowish or buff; tip of baculum more than 30 per
cent of length of shaft; shaft of baculum not widened at base.
_Eutamias amoenus_, p. 602

2'. Venter white; tip of baculum less than 29 per cent of
length of shaft - if more than 29 per cent, shaft widened at
base.

3. Size small to medium; greatest length of skull less
than 34 mm.; shaft of baculum not widened at base;
outermost dorsal dark stripe never obsolete _Eutamias
minimus_, p. 590

3'. Size large; greatest length of skull rarely less than
34 mm.; shaft of baculum widened at base; outermost dorsal
dark stripe often obsolete, never strongly evident.
_Eutamias umbrinus_, p. 606


ACCOUNTS OF SPECIES AND SUBSPECIES

Eutamias minimus (Bachman)

_Diagnosis._ - Size small; tip of baculum of adults less than 28 per
cent of length of shaft; outermost dorsal dark stripes distinct;
skull small to medium; when skull medium, zygomatic breadth not
proportionally narrower.

_Comparisons._ - From _Eutamias amoenus luteiventris_, the only
subspecies of that species in Wyoming, _E. minimus_ differs in:
Size smaller; tip of baculum in adults less than 28 per cent of
length of shaft; zygomatic arches proportionally wider; underparts
white or with less yellow or tawny.

From _E. umbrinus_, _E. minimus_ differs in: Size smaller; general
tone of upper parts lighter; base of baculum not widened but almost
as narrow as least diameter of shaft.

[Illustration: FIG. 1. Known occurrence and probable geographic
distribution of the subspecies of _Eutamias minimus_ in Wyoming. The
symbols for locality records are as follows: Circles, specimens
reported but not examined; solid circles, precise localities of
specimens examined; solid triangles, localities of specimens
examined, known only to county.

1. _E. m. minimus_
2. _E. m. consobrinus_
3. _E. m. pallidus_
4. _E. m. confinis_
5. _E. m. silvaticus_
6. _E. m. operarius_

From _E. dorsalis utahensis_, the only subspecies of this species in
Wyoming, _E. minimus_ differs in: Dorsal dark stripes distinct and
usually blackish; skull smaller; tip of baculum of adults less than
28 per cent of length of shaft.]

_Remarks._ - This is the smallest of the species of chipmunks in
Wyoming, and in the state can be readily distinguished from the other
species by the smaller size and by the characteristic proportions of
the baculum.

_E. minimus_ occurs in all the Life-zones of Wyoming, and inhabits open
country, such as in the great expanses where sagebrush (_Artemesia_
sp.) is predominant, or inhabits the edges of forests, never occurring
in the forest proper.

Analyses of measurements of the skull indicate that of the six
subspecies of _E. minimus_ that are found in Wyoming, two are small
(_E. m. minimus_ and _E. m. consobrinus_) and the other four are large
(_E. m. pallidus_, _E. m. confinis_, _E. m. silvaticus_, and _E. m.
operarius_). Within these size-groups the subspecies can be
distinguished by differences in color pattern.


Eutamias minimus minimus (Bachman)

_Tamias minimus_ Bachman, Jour. Acad. Nat. Sci. Philadelphia, 8(pt.
1):71, 1839.

_Eutamias minimus_, Miller and Rehn, Proc. Boston Soc. Nat. Hist.,
30:42, December 27, 1901.

_Type._ - Obtained on Green River, near mouth of Big Sandy Creek,
Sweetwater County, Wyoming. Age, sex, collector, and date when
obtained, not surely known.

_Diagnosis._ - Size small; general tone of upper parts pale grayish
brown; baculum small.

_Description._ - _Color pattern_: Crown Pinkish Buff mixed with
grayish white; facial stripes Snuff Brown mixed with black;
anterior margin of ear Drab washed with Cinnamon; hairs inside
posterior part of pinna Light Pinkish Cinnamon; posterior margin of
ear and postauricular patch grayish white; median dorsal dark
stripe black with Sayal Brown along margins; lateral pair of dark
stripes Sayal Brown more or less mixed with Fuscous; pairs of light
dorsal stripes grayish white and tinged with Buff; rump and thighs
Smoke Gray; dorsal surface of tail Fuscous Black mixed with
Cinnamon Buff; ventral surface of tail Sayal Brown or Clay Color,
Blackish Brown mixed with Cinnamon Buff around margins; antiplantar
and antipalmar surfaces of feet Pale Pinkish Buff; underparts
creamy white. _Skull_ and _Baculum_: Small but proportionally the
same as in other subspecies of _E. minimus_.

_Comparisons._ - From _E. m. consobrinus_, the subspecies to the
west and south, _E. m. minimus_ differs in: Over-all tone of upper
parts lighter; underside of tail lighter.

From _E. m. pallidus_, the subspecies to the north and northeast,
_E. m. minimus_ differs in: Size smaller; skull shorter and
narrower; mandible shorter and shallower; baculum shorter; slightly
paler.

From _E. m. confinis_, the subspecies in the Big Horn Mountains,
_E. m. minimus_ differs in: Size smaller; skull shorter and
narrower; mandible shorter and shallower; baculum shorter; paler.

From _E. m. operarius_, the subspecies to the east and southeast,
_E. m. minimus_ differs in: Size smaller; skull shorter and
narrower; mandible shorter and shallower; baculum shorter; paler.

_Remarks._ - _E. m. minimus_ is the smallest of the chipmunks that
occur in Wyoming. This pale little squirrel is found in the Red
Desert in Sweetwater County, where the features distinctive of the
subspecies are most strongly developed. Specimens from western
Sweetwater County and northwestern Uinta County are intergrades
between _E. m. minimus_ and _E. m. consobrinus_ and are referable
to _E. m. minimus_.

_Specimens examined._ - Total number 167.

_Sublette Co._: 60 mi. SE Jackson [Teton County], 1 (MM); 2 mi. SE
Big Sandy, 1.

_Fremont Co._: 40 mi. E Dubois, 1; 12 mi. N and 3 mi. W Shoshoni,
4,650 ft., 2; 9 mi. N and 3 mi. E Shoshoni, 4,700 ft., 2; 7 mi. N
and 3 mi. E Shoshoni, 4,700 ft., 3; 2-1/2 mi. W Shoshoni, 4,800
ft., 1; Granite Mountains, 6; Mount Crooks, 8,600 ft., 6.

_Natrona Co._: 27 mi. N and 1 mi. E Powder River, 6,075 ft., 2; 15
mi. N and 1 mi. W Waltman, 1; 9 mi. S and 9 mi. W Waltman, 6,950
ft., 1; 16 mi. S and 11 mi. W Waltman, 6,950 ft., 2; Sun Ranch, 5
mi. W Independence Rock, 6,000 ft., 4; 9 mi. W and 1 mi. N
Independence Rock, 1; 5 mi. W and 1 mi. S Independence Rock, 2.

_Uinta Co._: 15 mi. WSW Granger [Sweetwater County], 1; 10 mi. SW
Granger [Sweetwater County], 10 (MM).

_Sweetwater Co._: Farson, 6,580 ft., 11; 5 mi. E Farson, 1; 27 mi.
N Table Rock, 1 (MM); 27 mi. N and 37 mi. E Rock Springs, 6,700
ft., 1; 25 mi. N and 38 mi. E Rock Springs, 6,700 ft., 3; Junction
of Big Sandy Creek and Green River, 6,400 ft., 7 (3MM); 17 mi. N
and 6 mi. W Rock Springs, 7,000 ft., 1; Thayer Junction, 9 (MM);
Table Rock, 1 (MM); Wamsutter, 1 (MM); Green River, 4 (MM); Bitter
Creek, 2 (FC); 13 mi. S and 14 mi. E Rock Springs, 6,650 ft., 2; 18
mi. S Bitter Creek, 6,800 ft., 2; 22 mi. SSW Bitter Creek, 5; 26
mi. S and 21 mi. W Rock Springs, 3; Kinney Ranch, 6,800 ft., 21 mi.
S Bitter Creek, 15; 30 mi. S Bitter Creek, 2; 32 mi. S and 22 mi. W
Rock Springs, 1; 32 mi. S and 22 mi. E Rock Springs, 7,025 ft., 12;
33 mi. S Bitter Creek, 6,900 ft., 6; 3 mi. W Green River, and 2 mi.
N Utah Boundary, 1; 1/2 mi. N Junction Henrys Fork and Utah
Boundary, 2; 1 mi. N Linwood, Utah, 1 (MM).

_Carbon Co._: 18 mi. NNE Sinclair, 6,500 ft., 2; Rawlins, 1; 30 mi.
E Rawlins, 6,750 ft., 2; Bridgers Pass, 18 mi. SW Rawlins, 7,500
ft., 1.

_Additional records_ (Howell 1929:38): _Lincoln Co._: Fontanelle;
Opal. _Sublette Co._: Big Piney; Green River at junction with New
Fork; Muddy Creek, near Big Sandy Creek. _Fremont Co._: Jackeys
Creek, 3 mi. S Dubois; Wind River near mouth of Meadow Creek; Ft.
Washakie; Green Mountains, 8 mi. E Rongis. _Natrona Co._: Bitter
Creek, near Powder River; Rattlesnake Mountains; Casper;
Independence Rock. _Sweetwater Co._: Eden, Steamboat Mountain;
Superior; Maxon; Green River, 4 mi. N Linwood, Utah; Henrys Fork,
at mouth of Burnt Fork. _Carbon Co._: Canyon Creek, 12 mi. S
Alcova; Ferris Mountains; Shirley; Shirley Mountains; 8-1/2 mi. SE
Lost Soldier [= Bairoil]; Ft. Steele; Sulphur Springs. _Albany
Co._: Spring Creek, 10 mi. W Marshall; Sheep Creek. _County
uncertain_: Little Sandy River; Green River.


Eutamias minimus consobrinus (J. A. Allen)

_Tamias minimus consobrinus_ J. A. Allen, Bull. Amer. Mus. Nat.
Hist. 3:112, June, 1890.

_Eutamias minimus consobrinus_, Miller and Rehn, Proc. Boston Soc.
Nat. Hist. 30:42, December 27, 1901.

_Eutamias lectus_ J. A. Allen, Brooklyn Inst. Mus. Sci. Bull.
1:117, March 31, 1905 (not in Wyoming), type from Beaver Valley,
Utah.

_Eutamias consobrinus clarus_ Bailey, Proc. Biol. Soc. Washington,
31:31, May 16, 1918, type from Swan Lake Valley, Yellowstone
National Park, Wyoming.

_Type._ - Male, adult, skull and skin, No. 186456 (NM); from near
Barclay, Parley's Canyon, Wasatch Mountains, Salt Lake County,
Utah; obtained on October 31, 1888, by Vernon Bailey; original No.
361.

_Diagnosis._ - Size small; over-all tone of upper parts grayish
brown; baculum small, as in _E. m. minimus_.

_Description._ - _Color pattern_: Crown Smoke Gray mixed with
Ochraceous Tawny; upper facial stripe Fuscous; other facial stripes
Fuscous or Fuscous Black mixed with Tawny; hairs inside posterior
part of pinna Light Ochraceous Buff; anterior margin of ear
Ochraceous Tawny; posterior margin of ear and postauricular patch
grayish white; median dorsal dark stripe black with Ochraceous
Tawny along margins; other dorsal dark stripes black mixed with
Ochraceous Tawny; median pair of dorsal light stripes grayish white
with Ochraceous Tawny along margins; lateral pair of light dorsal
stripes white; sides Ochraceous Tawny or Light Sayal Brown; rump
and thighs Smoke Gray mixed with Cinnamon Buff; dorsal surface of
tail Fuscous Black mixed with Cinnamon Buff; ventral surface of
tail Sayal Brown, Fuscous Black along margin, and Cinnamon Buff or
Ochraceous Buff along outermost edge; antipalmar and antiplantar
surfaces of feet Light Pinkish Cinnamon or Pinkish Buff; underparts
grayish white mixed slightly with Buff. _Skull_ and _Baculum_:
Small but proportionally the same as in other subspecies of _E.
minimus_.

_Comparisons._ - From _E. m. pallidus_, the subspecies to the east,
_E. m. consobrinus_ differs in: Color darker; size smaller; skull
narrower and shorter; baculum shorter.

From _E. m. confinis_, the subspecies from the Big Horn Mountains,
_E. m. consobrinus_ differs in: Over-all tone of upper parts less
grayish; underside of tail lighter; skull narrower and shorter;
baculum shorter.

For comparisons with _E. m. minimus_ see the account of that
subspecies.

_Remarks._ - Specimens of this subspecies from the area between the
Uinta Mountains and the mountains of the Wyoming and Wind River ranges,
are clearly intergrades between _E. m. consobrinus_ and _E. m. minimus_


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