MAMMALS. 47 



contents of their stomachs iisiiiilly show a finely jnasticated mass of 

 green j^nlp, in which fil)ers of roots, bulhs, and ])lant steins may be 

 detected among the strealvS and spots of bright-colored th)Wcr and 

 berry stains, some particles of seed capsnles, and occasionally bits of 

 grasshoppers and other insect or animal remains. Their stomachs 

 are large and, except early in the morning, seem always to be filled 

 to their utmost cajiacity. The tender, starchy bidbs of the great 

 dogtooth violet are one of their favorite foods and often the moun- 

 tain sides are thickly pitted with little cavities from which the squir- 

 rels have extracted them. Camas and onions and other small bulbs 

 also are dug and eaten and the seed-laden heads of grasses are a 

 favorite autumn food. Toward the close of the season the squirrels 

 find more ripening seeds and these form a greater share of their food 

 than earlier. Consequently at this season they are taking on the 

 necessary winter's fat more rapidly and their appetites and capacity 

 seem to know no bounds. 



Usually four to six young are born early in May in the warm 

 grassy nests underground, and early in June these are beginning to 

 appear outside the burrows, Avhere they play aljout in interesting 

 little family groups. A month later they are half-grown, getting 

 their own food from the green plants, flowers, berries, and insects, 

 and are growing rapidly. By the first of September they are nearly 

 full-grown, and even the young have accumulated a considerable 

 quantity of fat inside their skins for winter fuel. 



The old males are the first to become very fat and hibernate, and, 

 strange to say, those at the lower levels hibernate considerably earlier 

 than those high up in the mountains, apparently because they have 

 had more time to accumulate their store of fat. The old females are 

 next to disappear, and last of all the later broods of young which 

 were still busily gathering food near timberline up to August 24, 

 long after inost of the animals had disappeared from the surface in 

 the low valleys. In their big warm nests deep underground they 

 sleep through the long winter, apparently without waking, as no 

 food is stored for winter use and they must depend entirely on their 

 supply of fat. Early in April they begin to reappear in the lower 

 part of their range, but it is probable that they are considerably later 

 in emerging from hibernation at the upper levels, which at that time 

 are still deeply buried in snow. 



Their winter dens are well made and the best of them are used 

 year after year. On July 27, at 7,000 feet altitude near Piegan 

 Pass, I selected one of the numerous large mounds over the mountain 

 side for a careful study of the den. A little fresh earth was being 

 added to the mound each day. A trap set at the entrance caught a mod- 

 erately fat old female that was evidently preparing her winter quar- 

 ters. The mound at the entrance of the burrow contained about -i 



