At all seasons they fill their cheek pouches with food to be carried away to their dens, but toward the end of summer or early fall they work industriously laying up stores of seeds and nuts. Sometimes these stores, hidden in chambers excavated for the purpose or in hollow logs and similar places, contain several quarts of beechnuts or other nuts or seeds. Small quantities of such food are hidden here and there under the leaves or in shallow pits in the ground. Store-rooms in one burrow contained a peck of chestnuts, cherry pits, and dogwood berries, and another had a half bushel of hickory nuts. [Illustration: ABERT SQUIRREL _Sciurus aberti_ KAIBAB SQUIRREL _Sciurus kaibabensis_] While at a summer camp I once saw one of these chipmunks give an exhibition of the exquisitely keen power of scent which must be necessary to recover scattered stores. The chipmunk had been coming repeatedly down a wooded slope in full view for twenty-five yards or more to the floor of the porch for food supplied by the campers. While it was absent carrying food to its burrow I placed a few nut meats on the flat top of a stump about fifteen feet to one side of the porch and farther away than the point where the chipmunk was being fed bread crumbs. On its return several minutes later, instead of going as usual to the porch, it ran directly to the stump, climbed up it, and promptly made off with the nuts, which it had evidently located from afar. They sometimes climb beeches and other trees to gather nuts even to a height of fifty or sixty feet, and are commonly seen on low limbs and in bushes. [Illustration: FLYING SQUIRREL _Glaucomys volans_] [Illustration: BLACK-FOOTED FERRET _Mustela nigripes_] The entrances to the burrows are usually under logs, roots, or rocks, or the den may be in a hollow log, stump or base of a tree, or even under a cabin in the woods. The burrows in the ground are commonly a series of tunnels some yards in length, with an oval nest and storage chamber two or three feet underground, and with branches from the main passageway. The nest chamber, a foot or more in diameter, is filled with fragments of dry leaves and other soft vegetable material. One chamber is usually used for sanitary purposes. The used entrance hole is commonly without a sign of dug earth about it, the loose soil from the burrow and its chambers apparently having been thrown out at another opening, which appears to be used for this purpose only and is kept plugged with earth. Throughout most of the northern half of its range these chipmunks usually hibernate from some time in October until March. Their hibernation is far less profound than that of the woodchuck and they not infrequently appear above ground during periods of mild weather, even in midwinter. The hibernating period is shorter in the southern part of the range.