supply and kind of soil. It would seem that centers of population may arise through the historical circumstance of original settlement by first-comers. This would be particularly the case in fields newly invaded, where descendants would establish their burrows in the near vicinity of their pioneer parents.
Digging operations were carried on by us during the breeding season of the ground squirrel, in quest of all obtainable facts in regard to their habits underground. Three general types of burrows were encountered. The male squirrels were usually found in short, shallow, simple burrows at the outskirts of the "colony." The burrow belonging to a male herewith illustrated (fig. 6) proved to be longer than usual with males,
Fig. 7. Plot (plan and elevation) of used nesting burrow of a female "digger" squirrel, as excavated by J. Dixon and G. R. Stewart on a west slope in Strawberry Canyon near Berkeley, April 6, 1918.
Entrance at left; old nest chambers at a; refuse sump at b; used nest at extreme right, which was found to contain the mother and four small young.
Total length of burrow, 22 feet; average diameter, 4½ inches; greatest depth reached, 30 inches; volumetric content, 44⁄5 cubic feet.
and reached to a greater depth, but its simplicity is characteristic for that sex. We failed to secure a single male squirrel in any burrow found to be occupied by a female with young. It is believed that at least during the breeding season the male squirrels live altogether by themselves in their own individual burrows.
A burrow from which a female and four young with eyes still unopened were secured is shown in fig. 7, It will be seen from this illustration that the nest burrow of the female is relatively complicated. This particular burrow was extremely difficult to follow on account of the many turns and "blind alleys."
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