Numerous holes in the sides of gullies and in the banks of washes form the most conspicuous signs of the presence of the Nelson Squirrel. Tracks and mounds at the entrances to burrows are not as noticeable as one would expect from the number and size of the animals. Trails from the burrows to the feeding grounds of this species are usually not well defined. In one place near the mouth of San Emigdio Creek these squirrels were obliged to cross a large dusty area in traveling back and forth between their burrows and their feeding grounds. Numerous tracks in this dusty spot showed that the squirrels in this colony did not follow definite trails, but that each individual chose his own route. In passing around a projecting bank, however, the tracks were found to converge for a short distance into broad, well-beaten paths six to eight inches wide.
The favorite location for burrows of this squirrel is, as already stated, in the sides of banks at the edges of washes or gullies. The burrows usually enter near the bottom of the bank. The entrances to the burrows vary from 1½ to 8 inches in diameter. The largest holes are in soft ground beneath horizontal hard strata in the bank and their large diameter is due at least in part to the weathering or caving in of the soft earth. The burrows of smallest diameter are found in hard, level ground at the roots of Atriplex bushes. The entrances to burrows in the banks are from six inches to fifty feet apart. These bank burrows run back in a generally horizontal direction and are interconnected to a considerable extent under the bank. This was proven by seeing a certain squirrel, known by sight to the observer, disappear into one hole and then in a few minutes reappear at the mouth of an adjoining burrow twenty or more feet distant.
All of the eight burrows dug into by various persons from this museum have proven to be simply refuge burrows, with only one entrance; that is, not of the intercommunicating type. Squirrels were found to reappear in from 5 to 15 minutes after they were chased into such burrows. These refuge burrows were found to be short, less than twelve feet in length; shallow, less than three feet in depth; and of small size, less than two inches in diameter. In three cases the squirrels were gassed in these burrows and an hour later dug out. Two of the animals were found dead near the wasteball at the entrance of the burrow, where they had evidently been overcome by the gas when attempting to make their way out.
No nests were found in any of the burrows that were dug out, although nesting burrows were particularly sought for. Consequently we have no information to offer regarding this phase of the animal's life history.
The Nelson Squirrels found near the mouth of San Emigdio Creek were found to be moderately infested with fleas. The squirrels were often seen to stretch out to their full length and roll over and wallow about in the fine powdery alkaline dust which in many places was an inch deep under the overhanging banks along the edges of the washes. Such dust baths, which were frequently indulged in with considerable evident satisfaction by the squirrels, are likely to serve in keeping the pelage of the animal clean as well as to discourage the fleas.
Our data regarding the breeding of Ammospermophilus nelsoni is scanty. The breeding season appears to be much earlier in this species than in the case of the Fisher Ground Squirrel in the same region.
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