Mountain deer and elk who usually range high during the summer go to the lowlands or several miles down the mountains for the winter. They may thus be said to migrate vertically. One thousand feet of descent equals, approximately, the climatic changes of a thousand-mile southward journey. They may thus winter from five to twenty-five miles from where they summered, from one thousand to several thousand feet lower. The elk that winter in the Jackson Hole region have a summer range on the mountains forty or fifty miles away. But elk and deer that have a home territory in the lowlands are likely to be found summer after summer in the same small, unfenced pasture. Moose, caribou, deer, and elk during heavy snows often resort to yarding. Moose and caribou are experts in taking care of themselves during long winters of deep snows. They select a yard which offers the maximum food supply and other winter opportunities. One snowy winter I visited a number of elk that were yarding. High peaks rose snowy and treeless above the home in the forest. The ragged-edged yard was about half a mile long and a quarter of a mile wide. About one half the yard was a swamp covered with birch and willow and a scattering of fir. The remainder was a combination of open spaces, aspen groves, and a thick growth of spruce. Constant trampling compressed the snow and enabled the elk readily to move about. Outside the yard they would have bogged in deep snow. In the swamp the elk reached the moss, weeds, and other growths. But toward spring the grass and weeds had either been eaten or were buried beneath icy snow. The elk then ate aspen twigs and the tops and limbs and bark of birch and willow. Ease of movement in this area enabled the elk to keep enemies at bay. Several times I saw from tracks that lion had entered this selfmade wild life reservation, and on two occasions a number of wolves invaded it. But each time the elk had bunched in a pocket of a trampled space and effectively fought off the wolves. One day late in February I visited the yard. The elk plainly had lost weight but were not in bad condition. While I lingered near the entire herd joined merrily in chase and tag, often racing then wheeling to rear high and fence with heads. If I counted correctly this herd went through the entire winter without the loss of an elk. But the caribou appears to be the only animal which migrates between summer and winter ranges, that is, which makes a long journey of hundreds of miles; as much change of place as made by many species of migrating birds. The main cause for this migration is the food supply, but myriads of mosquitoes in the woods may be one cause of the moose moving each summer far into the north where there are grassy prairies and large openings in the woods. But for winter they seek food and shelter in a yard in the forest.