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The attractive little white-tailed antelope 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 squirrels 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 squirrel 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...).
Other pages have pictures of the slightly larger and much less common San Joaquin antelope squirrel (A. nelsoni) and the Harris's antelope squirrel (A. harrisii) from southern Arizona and Mexico.
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