The hibernating habits of the grizzly are not completely understood. The custom probably originated, as did the hibernation of other animals, from the scarcity of food. In a long acquaintance with the grizzly my study of his hibernation has brought scanty returns, though all that I have actually seen has been of the greatest interest. The grizzly hibernates each winter,--"dens up" from three to four months. The length of time is determined apparently by latitude and altitude, by the snow-fall, weather conditions,--whether severe or mild,--and the length of the winter; and perhaps, also, by the peculiarities or the condition of the individual animal. Commonly he hibernates in high altitudes, many going to sleep near or above the timber-line. The place where he hibernates preferably is a natural cave or a large opening beneath rocks. If completely sheltered in a cave, he is commonly satisfied to lie on bare rocks, with nothing over him. In other places, where the snow might come in contact with him, he commonly crawls beneath a huge pile of trash, leaves, sticks, and roots. Snow had drifted deeply over each hibernating-place I have found. That his winter-sleep is more or less restless is shown in the spring by his hairless hips and sides, the hair having been worn off during the winter. This probably is due to frequent turnings from side to side. He is generally fat when he turns in for his winter's sleep; but usually he does not eat anything for a few days before going in. On the few occasions on which I was able to keep track of a bear for several days before he went to sleep he did not eat a single thing during the four or five days that immediately preceded retiring. I have examined a number of grizzlies that were killed while hibernating, and in every instance the stomach and intestines were entirely empty and clean. These facts lead me to think that bears do not eat just before hibernating. Nor do they at once eat heartily on emerging. The instances in which I was able to watch them for the first few days after they emerged from winter quarters showed each time almost a fast. Those observed ate only a few ounces of food during the four or five days immediately after emerging. Each drank a little water. The first thing each ate was a few willow-twigs. Apparently they do not eat heartily until a number of days elapse. On one occasion I carefully watched a grizzly for six days after he emerged from his hibernating-cave. His winter quarters were at timber-line on Battle Mountain, at an altitude of nearly twelve thousand feet. The winter had been of average temperature but scanty snow-fall. I saw him, by chance, just as he was emerging. It was the first day of March. I watched him with a field-glass. He walked about aimlessly for an hour or more, then returned to his sleeping-place without eating or drinking anything.