CHIPMUNKS Genus Tamias
in the squirrel family Sciuridae

Chipmunks are small striped squirrels (genus Tamias) in North America. The first thing for a field observer to recognize is that a chipmunk is different from the only other squirrel that is vaguely similar, the Golden-mantled Ground-Squirrel (left). That colorful squirrel is widespread and easily visible in wooded open country in the mountains throughout western North America. It can be very tame in National Parks like this one in Yosemite. Note that although the Golden-mantled Ground-Squirrel has black-and-white body stripes it lacks any stripes on the face. It is not a chipmunk. All chipmunks have facial stripes. It is difficult to separate them in the field and to tell you the truth I'm putting this page together in hopes I can learn something. I've had unlabelled slides in my files for much too long!

I have two excuses for putting off learning chipmunks for this long. First, I had a job in college skinning birds and mammals for the taxidermy collection at my small rural school. When I was taught to skin chipmunks and squirrels I learned that one must look for and locate the bacula -- the penis bone -- on all males, and tie it to the label on the specimen. It sounded very weird to me at the time, and it still sounds pretty strange today (and no, I'm not making this up). Indeed, if you read Ingles (1965) seminal book on Pacific coast mammals he has a whole appendix on "technique for preparing and preserving bacula" and a page of drawings comparing the bacula of chipmunks. Believe me, it is pretty hard to look for the bacula of chipmunks in the field! [... and in some species the female genital bones -- baubellum -- is also distinctive.]

Second, where I live in Monterey County, California, there is only one chipmunk -- the Merriam's Chipmunk (right or above) -- and therefore no field problems to be worked out. Its habitat and range is chaparral or foothill woodland in the southern half of California" but "may extend up to 7,000 feet in open coniferous forest or pinyon-juniper woodland" (Ingles 1965). This photo is at 5,000' elevation in the Santa Lucia Mts. where the chipmunk was venturing up the skeleton of a burned chaparral shrub after a recent fire. It field characters include the fact that the body stripes are gray and dark brown and that these stripes lack clear demarcation; that the head stripes are brown (black only just before and after the eye); that the back side of ear is unicolored, grayish or buffy; and the fact that the tail is long, usually over 80% of head & body length. All these characters are apparent in this photo.

It is in the Sierra Nevada that chipmunks become a major challenge. Nine species are zonally distributed in the central Sierra from Merriam's Chipmunk (above) in the foothill chaparral to Alpine Chipmunk Tamias alpinus in the talus slopes up near tree level to Panamint Chipmunk T. panamintinus of pinyon-juniper woodlands east of the divide. Ingles (1965) explains that chipmunks well illustrate both the biological principle of Gloger's Rule (that a species of mammal is more heavily pigmented in the more humid areas) and have evolved patterns best suited to their habitat. Thus Merriam's Chipmunk, which lives in dense chaparral where the shadows are not sharply defined, has dingy stripes. Likewise the Alpine Chipmunk which exists in open talus slopes has poorly demarcated stripes. But other species (Least, Lodgepole, Yellow Pine chipmunks) that "inhabit sunlit open forests where light-bathed twigs cast dark shadows" have well-defined light and dark stripes. This character is illustrated by this chipmunk (left) at the base of a huge Giant Sequoia; note how bright the white stripes appear in the dappled light of the understory. This photo may be inadequate for identification but it does illustrate this principle.

According to Johnson (1943) there can be more variation in the coloration of a single chipmunk over the course of a year that there is between species. Sutton (1962) showed differences in chromosomes and some taxonomic changes have been adopted largely on genetic grounds. All of these points make for discouraging reading when thinking about field identification. But Harris (1982) brightens things up be stating that "Fortunately, chipmunks tend to occur in fairly distinct habitats in a given region, so that it is possible to eliminate some species from consideration" although one "must exercise care since the distributional status of some species may be incompletely known."

Using the criteria in Harris (1982), Burt & Grossenheider (1976), Ingles (1965), and, most importantly, the recent monograph by Wilson & Ruff (1999; includes color photos of each species) the chipmunks below are identified as Least Chipmunk (left) and Lodgepole Chipmunk (right). Note that both have well-defined essentially black-and-white stripes compared to the dark-brown and grayish stripes of Merriam's Chipmunk shown above.

The Least Chipmunk (above left) is the common small chipmunk of sagebrush below the pinyon/juniper zone. Its range extends across the entire Great Basin (and I happen to know the photo is of that species because it is the only chipmunk that ranges to northwestern Wyoming where this shot was taken). Because of its wide range and variety of habitats it is the most variable of all chipmunks, but it is also the smallest and has very short ears. It is said that where its range overlaps other species it is dominated by larger chipmunks and therefore restricted to sage and brush habitats. It has much gray to the shoulders and rump, and the striping pattern is sharp. It often runs with its bushy tail held straight up.

Compare the ear size of Least to the somewhat larger Lodgepole Chipmunk (above right). Not only are the ears large but there is a bright white patch behind the ears. The sides are rather bright orange, contrasting with the white body stripes, but there is no outer dark stripe on the body as on Least (left) or Yellow Pine Chipmunk T. amoenus. Note that the shoulders and rump are also washed with orange coloration (not gray as as in the otherwise similar Panamint Chipmunk).

The Alpine Chipmunk (right) is small, rather like the Least, but has longer and more pointed ears, much less distinct body stripes, and is overall gray in appearance. The back of the ear is concolored gray without a white patch. Note also the very black facial stripes. It does have a dark outer stripe on the body and essentially lacks the orangeish sides of Lodgepole Chipmunk [Unita Chipmunk T. umbrinus of the eastern Sierra and isolated Great Basin Mts. lacks the dark outer stripe but has subdued orangeish sides.] The Alpine Chipmunk is usually found above 8,000' elev. (Burt & Grossenheider 1976), or even above 9,000' elev. in the Yosemite Sierra (Ingles 1965, Harris 1982) but my photo was taken at 7,500' elev. in Sequoia Nat'l Park somewhat farther south in the range and at its lowest known elevation limit (Wilson & Ruff 1999).

In researching this page I found a lot of differences in taxonomy between the older texts (Burt & Grossenheider 1976, Ingles 1965, Harris 1982) and newer publications (Jameson & Peeters 1988, Laudenslayer 1991, Wilson & Ruff 1999). Obviously, sometime in the mid-1980s the genus of all chipmunks was revised from the old Eutamias to the current Tamias. Various groups in northeastern and northwestern California were split into several species. There is also much variation in English names but I prefer the names used by Daniel F. Williams in his on-line Checklist of California Mammals. In all but one case these are the names used by Wilson & Ruff (1999; the one exception is discussed below). There are now 13 chipmunks in California as follows (ranges & habitats are generalities; see the texts cited for more specifics. Ranges overlap in numerous locales):

One important point of difference between older and newer taxonomies has been the splitting of the Townsend's Chipmunk complex into four species by Sutton & Nadler (1974) and Sutton (1987). "Townsend's Chipmunks" in the broad sense were the large dark chipmunks of the Pacific Northwest. Now, Townsend's Chipmunk T. townsendi (sensu stricto) is limited in range to Oregon & Washington & s. British Columbia with Yellow-cheeked, Siskiyou, and Allen's Chipmunk occupying various portions of California and southern or eastern Oregon. The splits were based on an analysis of the genital bones (baculum and baubellum) and genetics but also on differences in calls. Siskiyou Chipmunk has a one syllable call that starts at low pitch, rises, and than falls again (looked like an inverted chevron on a sonogram). Yellow-cheeked has a distinctive low-pitched two-or-three syllable "chip-chip" or "chip-chip-chip" pattern. I was just learning about these points in summer 2001 when Rita & I visited Van Damme State Park in Mendocino Co., California. While walking the Fern Canyon trail in a lush wet coastal forest we heard a "chip-chip-chip" sequence numerous times from well up on the mossy limbs of a Bigleaf Maple. I passed it off as a squirrel call but Rita insisted I track it down. It turned out to be my lifer Yellow-cheeked Chipmunk (both photos below).
Note that Yellow-cheeked Chipmunk is also a dark and dingy beast. Indeed, only its central stripe was very apparent on the body. The facial stripes were well-marked, though, and there was a big white patch behind the ears. Note also the bicolored pattern on the back of the ears: dark in front and white behind. The other chipmunk in range here (but usually more inland) is Sonoma Chipmunk which is much redder and has unicolored backs of its ears in summer (but not winter) pelage. I was quite impressed to learn that, like birds, state of plumage (er, pelage) and molt can be important to field identification and that vocalizations can be distinctive and useful!

Since encountering the Yellow-cheeked Chipmunk in July 2001, I've come across "Townsend's" type chipmunks on two other trips to Northern California. The Allen's Chipmunk (right) is the large grayish chipmunk with a rather wide range from coastal Humboldt County (between Eel and Klamath Rivers) to well inland in the mountains. I photographed this one (right) near Lassen Nat'l Park. Note the subdued patterning and clay-colored sides to a grayish chipmunk. This is also a large chipmunk, especially when contrasted with a small chipmunk like the Yellow-pine Chipmunk (below), a bright-sided contrasty little beastie that occurs at higher elevations in Lassen Park.
Of course the first few chipmunks one sees look "small" so it is initially difficult to sort out chipmunks by size. But as one gains some experience with a variety of species the California species start falling into recognizable patterns: big grayish ones (the "Townsend's" group that include Allen's, Yellow-cheeked, and Siskiyou), the bright little ones (Lodgepole, Yellow-pine), the red one (Sonoma) and so on. As to the "bright little ones" note how Yellow-pine (left) has a nice black outer stripe while Lodgepole (shown above as the 2nd & 4th chipmunks on the page, not counting the ground-squirrel) does not.

I'm still sorting out the "Townsend's" group and need more field experience and more details. Must the "Townsend's" type that I saw in the riparian along the south side of the Klamath River (loosely associated with a mixed bird flock centered around Black-capped Chickadees) be an Allen's while one north of the same river is a Siskiyou? Don't know yet but this is a fun project!
 

I'm not going to be able to do much with the final photo in my collection since it's not much of a shot. As it was taken in Cave Creek Canyon in the Chiricahua Mts. of southeast Arizona, it is apparently of a Cliff Chipmunk (below) that is the only species in range. The Cliff Chipmunk actually is has a gray chipmunk with rather dingy pattern (as you can tell from this dingy photo... ahem).

California has the bulk of North America's chipmunks with 13 species. The remaining nine chipmunks in North America are:

Vladimir Dinets tells me that there is one chipmunk in the Old World -- Tamias sibiricus -- and he provided this photograph taken in SE Siberia. Dinets says that "it resembles western American species but is biochemically and morphologically close to Eastern Chipmunk. A Japanese race is sometimes considered a separate species, but Sakhalin population is clearly intermediate between it and nominate sibiricus." Finally, there are two additional chipmunks in Mexico. This brings the world total to 25 species of chipmunks.

Like ground-squirrels, chipmunks are diurnal mammals and hibernate in cold weather. They have internal cheek patches for carrying food. Unlike most ground-squirrels which store fat for energy during dormant periods, chipmunks have large underground caches of food the the occasional periods of waking and for use in early spring in areas still covered by snow. Seeds and fruits constitute most of their diet although the Least Chipmunk eats a fair amount of insects and even lizards. More details are in Ingles (1965).

Bottom line on chipmunks: when in doubt, check the bacula!

PHOTOS: The Golden-mantled Ground-SquirrelSpermophilus lateralis was at Olmstead Pt., Yosemite Nat'l Park, 11 July 1981. The Merriam's Chipmunk Tamias merriami was at China Camp, Los Padres Nat'l Forest, Monterey Co., California, in April 1984. The chipmunk at Grant Grove, Kings Canyon Nat'l Park, in June 1997, is probably the Lodgepole ChipmunkEutamias speciosus. The Least Chipmunk Tamias minimus was at Devils Tower Nat'l Monument, Wyoming, 15 June 1998. The Lodgepole Chipmunk Tamias speciosus was at Devils Postpile Nat'l Monument, Madera Co., California, 19 Aug 1998. The Alpine Chipmunk Tamias alpinus was along the High Sierra trail in Sequoia Nat'l Park, Fresno Co., California, 20 June 1997. The Yellow-cheeked Chipmunk Tamias ochrogenys was in Van Damme State Park, Mendocino Co., California, 30 June 2001. The Allen's Chipmunk Tamias senex was at Battle Creek campground near Lassen Nat'l Park, Tehama Co., California, 15 August 2001 and the Yellow-pine Chipmunk Tamias amoenus was in Lassen Nat'l Park itself, just on the Tehama-Shasta Co. line, that same day. The Cliff Chipmunk Tamias dorsalis was at Cave Creek, Chiricahua Mts., Arizona, in July 1984. The Siberian Chipmunk Tamias sibiricus was at Oo, Buryatia, in SE Siberia, in July 1984. All photos © 2001 Don Roberson,  except that of Tamias sibiricus provided by Vladimir Dinets & used with his permission; all rights reserved.

Literature cited:

Burt, W. H., and R. P. Grossenheider. 1976. A Field Guide to the Mammals. Houghton Mifflin, Boston.

Harris, J. H. 1982. Mammals of the Mono Lake-Tioga Pass Region. Kutsavi Books, Lee Vining, CA.

Ingles, L. G. 1965. Mammals of the Pacific States. Stanford Univ. Press, Stanford, CA.

Jameson, E. W., Jr., and H. J. Peeters. 1988. California Mammals. Univ. of Calif. Press, Berkeley.

Johnson, D. H. 1943. Systematic review of the chipmunks (genus Eutamias) of California. Univ. Cal. Publ. Zool. 48: 63-148.

Laudenslayer, W. F., Jr. 1991. A check-list of the amphibians, reptiles, birds, and mammals of California. Calif. Fish & Game 77: 109-141.

Sutton, D. A. 1962. "Chromosomes of some Sciuridae," abstract of paper given before the Western Society of Naturalists, San Jose, CA, cited in Ingles (1965).

Sutton, D. A. 1987. Analysis of Pacific coast Townsend's Chipmunks (Rodentia: Sciuridae). Southwestern Naturalist 32: 371-376.

Sutton, D. A., and C. F. Nadler. 1974. Systematic revision of three Townsend's Chipmunks (Eutamias townsendii). Southwestern Naturalist 19: 199-211.

Wilson, D. E., and S. Ruff. 1999. The Smithsonian Book of North American Mammals. Smithsonian Instit. Press, Washington, D. C.

TOP
RETURN TO MAMMALS PAGE

GO TO LIST OF FAMILIES OF THE WORLD

GO TO BIRDING THE WORLD PAGE

RETURN TO HOME PAGE

Page created 7-23 June 2001, revised 2 & 11 July 2001, and again 14 Sep 2001