As has been shown by Allen, the species of birds of the temperate and boreal zones of North America were derived in part from the Old World, in part from types almost universally distributed throughout the warmer latitudes, and in part from tropical America, but to a marked extent the species present developed where they are now found. This generalization is in harmony with the geographical relations of the continent to other land areas, and with the fundamental principles of evolution. _Migrations._--Among the many facts of interest to the geographer in connection with the bird life, none present a more fascinating field for study than the annual migrations in which a very large number of the species participate. As one travels northward from Mexico or the Gulf States, the number of species of birds which remain in essentially the same area throughout the year, or the _residents_ as they are termed, becomes less and less. In New England and about the southern shores of the Great Lakes there are about 30 species which remain all winter and may justly claim to be citizens. Besides these, there are several visitors that come from the north and belong to the vast army of migrants, but which are contented with a comparatively small change of position during the periods of greatest cold or heaviest snow. In the far north the number of residents is still more restricted. On the tundras fringing the arctic coast even the snow-owls, snow-buntings, and the ptarmigans, the hardiest of birds, move southward during the winter to the shelter of the subarctic forest, and bird life on the vast frozen morasses is practically, if not absolutely, wanting. The millions of birds that journey southward each fall begin their return migrations at the first promise of spring. Even during unusually mild spells of weather in winter, temporary northward movements occur. The migratory birds are actuated by such a strong desire to regain their nesting places and summer homes that they embrace every opportunity to journey towards them, and not infrequently suffer severely for the risks they take. In some instances species which have begun their northward flight too soon are killed by thousands owing to a return of severely cold weather or die for lack of food.