MIGRATION OF ANIMALS. The word mi gration is it-eil in two sen-es: either to refer to thew periodical deluges of such as are made by Many spades of bird.: and by some mammals. and by a few insects: or to those irregular dispersion, by oven.rnwiling and lark of food or water.
NI In mAt-.-. Among mammals migrations in the first sense are mainly efaifined to certain d neva. which gul a rly move from and In the polar -pa-. with the alternat hig seasons. Regular seasonal movements, truly migratory but short. are practiced by many land animals, especially the herbivores. All deer, goats. sheep. antelopes. and the like, which dwell in mountainous regions, regularly ascend the heights in early summer to get the new find safer solitudes. escape the lowland (lies, and otherwise better themselves. In the fall they come down as the snow and cold increase upon the heights, and seek the valleys or the neighboring plains. The American bison formerly was wont to retreat from the moun tains to the plains during severe winters, while those on the northerly plains tended to move south. Before the time of railroads the great body of the pronghorns of the plains used to migrate from the northern area of their range to the milder regions south of the Platte River. and returned north in the spring. Still more
striking is the regular and prolonged annual migration of the caribou from the Arctic shores of America to the southerly interior, especially in the region north and east of Hudson Bay; they cannot live so far north during the winter, but go back as soon as the snow melts in spring. In all these cases there is an accompanying migra tion of certain large predaceous animals, such as wolves, which depend upon the grazers for food. Similar facts may be cited from the plain re gions of Asia, Australia, Patagonia. the Sahara, and South Africa, where seasonal changes, either of cold or drought or the parching of pasturage, compel annual migrations to and from other regions not far distant. It will he seen that these movements are under compulsion of the lack of food (or frequently in desert regions of water), and are continued only when and so far as is necessary. Mammals are too slow and hampered in their movements on land to make long, rapid journeys, such as a bird or fish is able to accomplish through unobstructed air or water; and most mammals either can find food all the year round. or have acquired the power, by storage of provisions or by sinking into dormancy, of tiding over the seasons of scarcity.