White-tailed and San Joaquin antelope ground squirrels
The attractive little white-tailed antelope ground squirrel(Ammospermophilus leucurus) is famous among thermoregulatory physiologists and desert ecologists because it is one of very few small desert mammals that remains active aboveground on the hottest summer days. They manage to keep body temperature under control -- despite much hotter ground and air temperatures, and strong sunlight -- by shuttling between open areas and cool refuges, like burrows. When body temperature gets too high (up to about 43-44 C, or 110 F), they run to a cool spot, sprawl on their bellies, and passively cool off without losing water by sweating or panting (below, right). Then they get up and run around some more. Their white undertail -- the source of the 'antelope' name -- is usually carried curled over the back, where it helps reflect sunlight and shade the body (as in the above right photo). These antelope squrrels were photographed in Joshua Tree National Park and in Deep Canyon (near Palm Desert, California) on warm spring days; the pictures were taken around mid-day and I used fill-in flash to soften the harsh shadows The squrrel below at left is a nursing mother, and the one two rows down is, obviously, an adult male in full reproductive condition (I don't like to think about all the cactus spines these guys run over during an average day...).
San Joaquin antelope squirrels:
Images copyright by Mark A. Chappell
The bottom two images on this page are of the closely-related San Joaquin antelope squirrel (A. nelsoni), found in the San Joaquin Valley (the southern part of California's 'Central Valley'), and a few adjoining areas. This species is now endangered because most of its habitat has been converted into farmland and subdivisions. They seem to do well in some cattle ranches, and the two individuals at the bottom of the page were photographed on ranchland in the Panoche Valley (a dry wash on the western edge of the San Joaquin Valley). I apologize for the poor quality of these images; they were scanned from Kodachrome slides taken in 1974.
