Page:Natural History of the Ground Squirrels of California.djvu/119

Rh of the lower levels; but the metropolis of the species is in the middle region among the salt-bushes (Atriplex) which thickly dot these plains.

This ground squirrel is soon driven out when fields come under cultivation. It clings closely to the wild land and apparently rarely if ever invades adjoining ground which may happen to be under cultivation. Thus in May, 1918, at the mouth of San Emigdio Creek, Kern County, we found these squirrels quite abundant on three sides of an extensive alfalfa field which was entirely surrounded by virgin tracts of the salt-bush (Atriplex), yet during our stay of nearly two weeks, not a single Nelson Squirrel was observed to enter this field or even to touch a leaf of the alfalfa.

As usually encountered, the Nelson Squirrels are seen scurrying rapidly across open places between clumps of salt-bushes, or else, more rarely, standing straight up to their full height in true "picket-pin" fashion just before they disappear down their burrows. The normal mode of travel is by a series of short rapid jumps of from 6 to 12 inches. When approaching a hole leisurely, or when foraging about, the animals sometimes slow down into a walk.

These squirrels are not early risers, being rarely found abroad until well after sun-up. At the mouth of San Emigdio Creek, during the second week in May, Nelson Squirrels began to appear at the entrances to their burrows in the south-facing overhanging bank of a wash, between 8 and 8:15 in the morning. They appeared earlier in the day at this point than elsewhere in the vicinity, doubtless because this bank first received the full force of the early morning sun. Ten o'clock marked the period of greatest activity. The squirrels under observation disappeared each day between 11:30 and 12 o'clock and were rarely seen again until 2:30 in the afternoon, when they began to reappear in the shade of certain dense-foliaged salt-bushes that grew on the brink of the wash. Although they were frequently seen to bask in the rays of the early morning sunshine, these squirrels shunned the direct sunlight at noonday. As early even as 10 o'clock in the morning one female was seen repeatedly to seek shelter in the shade of a fencepost (J. Dixon, MS).

The tail of the Nelson Antelope Squirrel, as with the Desert Antelope Squirrel, is the most conspicuous feature about the animal. When running, the tail is curved forward over the back, in which position the creamy under surface is most effectively displayed so that at a distance one receives the impression that merely a bit of thistledown is blowing along over the sand. The body of the animal, with its ground-like tone of color, practically disappears. This illusion is furthered by the twitching of the tail and by the momentary pauses of the animal which correspond closely with the usual interrupted flight of a tuft of thistledown.

When the squirrel is foraging about on all four legs, or else sitting up, the tail is held curved forward over the back; in fact, one rarely sees the tail held in any other position (see fig. 28). At such times the tip of the tail is often curved slightly upward or outward. When excited or frightened the tail of the animal is twitched rapidly fore and aft, but rarely or never sideways. One individual observed at a distance of ten feet was seen to vibrate its tail intermittently with exceeding rapidity, there being half-minute intervals between the periods of