In Alaska and the Northwest many bears hibernate in the heights above the timber-line. I have found a number in the mountains of Colorado with winter quarters at an altitude of twelve thousand feet. In southern Colorado and in the Yellowstone Park region many have denned up at about the altitude of six thousand feet. But a grizzly may hibernate anywhere in his territory where he can find or make a den to his liking.
Except when there are cubs, a grizzly dens alone. Accounts which tell of a number of full-grown grizzlies spending the winter in one den lack verification. The cubs are born in the hibernating-den, and they den up with the mother the first, and sometimes the second, winter after their birth. The cubs generally den up together the first winter after they are weaned.
Once in for the winter, the bear is likely to stay in the den for weeks. Most of the time probably is spent sleeping, and, so far as known, without either food or water. A bear may be routed out of his winter quarters without difficulty. Generally his sleep is not heavy enough greatly to deaden his senses. Hunters, trappers, floods, and snow-slides have driven grizzlies from their dens during every stage of hibernation, and in each case a moment after the bear came forth his senses were as alert as ever; he was able either to run away or to fight in his normal manner.
Prospectors in Jefferson Valley, Montana, told me of staking claims and starting to drive a tunnel early one December. A day or two after they began blasting they saw a bear break out of a snowy den and scamper away on the mountain-side. They tracked him to the place where he had holed up again. It was their belief that the noise or the jar of their shots had awakened and re-awakened the bear, until, disgusted, he left the region for a quieter sleeping-place.
A sniffling and grunting attracted my attention one midwinter day as I was snowshoeing along the side of a ravine. Presently, a short distance ahead of me, I saw a grizzly’s nose thrust out of a hole in the snowy slope. Then his head followed. Sleepily the grizzly half-opened his eyes, then closed them again. His shaking and drooping head fell lower and lower, until with a jerk he raised it only to let it droop again. He repeated this performance a number of times. Evidently it was the head of a very sleepy grizzly. Occasionally he opened his eyes for a moment, but he did not seem interested in the outside world and he finally withdrew his head and disappeared in the den.
After midwinter, and especially towards spring, a bear sometimes comes out for fresh air and exercise, or to sun himself. One gray February day, snowshoeing along the Big South Poudre, I chanced to look across an opening from the edge of the woods and saw a grizzly walking round and round in a well-beaten pathway in the snow. Occasionally he reared up, faced about, and walked round in the opposite direction. His den was near by. Half a mile farther on I came upon a bear trail near the entrance to another den. Here the bear had walked back and forth in a pathway that was about sixty feet long. It was beaten down in the snow to a depth of fifteen inches. Two places showed that the bear had rolled and wallowed about in the snow.
Elsewhere, another year, about the middle of March, I examined much-worn pathways near a grizzly’s den. These had been made at least three weeks before and had been used a number of times. One pathway led to the base of a cliff that faced the east, where the bear had probably lain in the morning sun. Another led to a much-used spot that caught the afternoon sun.
Perhaps a bear sometimes becomes tired or restless during his long winter sleep. Now and then he comes forth in spring with the fur worn off his hips, back, or shoulders. He may kill time, when through sleeping, with a short excursion outside the den. If the den is large, he sometimes tramples about like a caged animal.
Climatic conditions, the altitude at which the bear hibernated, and other factors determine the time when grizzlies leave their dens. Most of them come forth during March, but stragglers may not appear until late in April. Mothers with cubs remain in the den a few weeks longer than bears without cubs.
At the limits of tree growth, one cold March day, I came upon the tracks of a grizzly bear descending the mountain. I back-tracked them and found the den in which the grizzly had spent the winter. The inside of the den was gravelly and comparatively clean. Only this single line of tracks led from the den, though the weather had been clear for a week; so I judged this was the first time the grizzly had sauntered forth. It was just sundown when I reached the den. The heights were icy, and I hesitated about continuing across the Divide that night, so concluded to occupy the den. I knew that bears often take a short ramble in the spring and then return to the den, but I took the chances of sharing it with him. I do not know what the grizzly did that night—whether or not he came back. But my fire in the mouth of the den may have kept him at bay.