A recent revision changed the taxonomic picture; until this revision, five species of our region were placed in the genus Spermophilus. The genus now is considered to be limited to the Old World and the various species in our region have been assigned to the four genera noted above. The Golden Mantled Ground Squirrel (Callospermophilus lateralis) is an inhabitant of highland forests in the northern mountains of New Mexico and in the Mogollon Complex in west-central New Mexico. With its distribution north and northwest of the Chihuahuan Desert Region, it apparently never made it to the mountain ranges bordering the eastern side of the Rio Grande Valley south of the Sangre de Cristo Mountains of northern New Mexico. Presumably, the lowlands south of that mountain range were too hot and dry to support the squirrel by the time the northern mountains could be re-inhabited following the last glaciation.
With its single white lateral stripe, this squirrel frequently is misidentified by laypeople as a chipmunk. Lack of facial and dorsal striping, however, immediately removes it from that group, and the skull also differentiates it from the chipmunks.
The Mexican Ground Squirrel (Ictidomys mexicanus) enters our region from the southeast. Despite range maps showing a westward range north of the Rio Grande to the vicinity of El Paso, there appears to be no specimens from this far west. The Pecos Valley, however, is inhabited. Three somewhat similar species of ground squirrels are identifiable by the nature of their dorsal markings. This species has rows of light-colored spots; the Thirteen-lined Ground Squirrel (Ictidomys tridecemlineatus) alternates stripes and rows of spots, while the Spotted Ground Squirrel (Xerospermophilus spilosoma) has pretty much disorganized spots.
The Spotted Ground Squirrel occurs throughout the region in the flat and rolling terrain below woodland and forest. It is by far the commonest ground squirrel in the non-montane areas.
The Thirteen-lined Ground Squirrel is predominately an eastern plains grassland type that enters the eastern portions of our region, though absent in the southern areas of New Mexico; it has apparently disjunct relictual populations in west-central New Mexico and adjacent Arizona.
The largest of the ground squirrels of the region is the Rock Squirrel (Otospermophilus variegatus), whose general appearance is more like that of a tree squirrel than the other ground squirrels. This mottled black/white/gray squirrel occurs throughout our region, generally in rocky, rough terrain. On occasion, however, it may occur a ways out into intermontane basins where steep-sided arroyos afford burrowing sites. It appears to climb into trees more often than the other ground squirrels.
Three species of antelope squirrels (Ammospermophilus) occur in the region, separated geographically. The White-tailed Antelope Squirrel (A. leucurus) occupies the northwestern quadrant of New Mexico; the Texas Antelope Squirrel (A. interpres) east of the Rio Grande in the U.S., but continuing south into eastern Chihuahua in Mexico; and Harris' Antelope Squirrel (A. harrisii) into the bootheel of New Mexico. The type locality of the Texas Antelope Squirrel is El Paso.
In northwestern New Mexico, the White-tailed Antelope Squirrel frequents sandy soils; the other species in our region generally occupy rocky, rough terrain.
Two species of prairie dogs occur in the region. The Black-tailed Prairie Dog (Cynomys ludovicianus) occupies the grasslands of Trans-Pecos Texas. all but the northwestern quadrant of New Mexico, and northwestern Chihuahua, Mexico (a related species, C. mexicanus, occurs in southern Coahuila and northern San Luis Potosíi in northern Mexico); Gunnison's Prairie Dog (C. gunnisoni) inhabits the remaining grasslands of New Mexico.
The Black-tailed Prairie Dog, once occurring in the millions in the Great Plains and west to southeastern Arizona, has been badly decimated, primarily by government-sponsored campaigns to eradicate them from grasslands occupied by livestock.
Chipmunks (Tamias) are widespread in the Southwestern highlands. Unlike the striped ground and antelope squirrels, chipmunks have both facial and dorsal stripes. Included within our region are the Gray-footed Chipmunk (Tamias canipes), distributed in the mountains east of the Rio Grande from central New Mexico to the Guadalupe Mountains of New Mexico and Texas; the Gray-collared Chipmunk (Tamias cinereicollis) of the western Mogollon Mountains complex; the Cliff Chipmunk (Tamias dorsalis) throughout the western mountains of New Mexico south of the San Juan Basin and continuing south through western Chihuahua; the Least Chipmunk (Tamias minimus) in the northern mountains of New Mexico and with relictual populations in the Sacramento and White mountains of south-central New Mexico; and the Colorado Chipmunk (Tamias quadrivittatus) in the northern quarter of New Mexico and with an isolated population in the Organ Mountains of south-central New Mexico.
Generally chipmunks divide up the habitat elevationally when more than one species occurs in a mountain range. Thus the Least Chipmunk tends to abandon the lower elevations to other species. The Cliff chipmunks, on the other hand, tends to occupy the lower elevations; in the absence of other species, it ascends to higher elevations.
Last Update: 10 Aug 2009
Centennial Museum and Department of Biological Sciences, The University of Texas at El Paso