While the winter habitat of most birds in the temperate and boreal portions of the continent is to the south of their summer homes, the annual migration is not in all cases great in amount. Some species move only a few hundred, or possibly a few score, miles. Even the winter residents make short migrations, dependent on weather conditions. The greater part of the migratory birds, however, pass the winter in the Gulf States, Mexico, the West Indies, and Central and South America. In some cases they go well to the south of the equator. The annual flight going and coming measured in a straight line, between the nesting place and the winter home, cannot be less in many instances than from 8,000 to 10,000 or 12,000 miles. An interesting fact in this connection is that certain species follow definite routes. The region moved over annually, if marked on a map, would resemble two open or partially opened fans, with their handles pointing towards each other and connected by a narrow band. The causes of the annual migrations of birds have received much study and been the subject of much speculation. The general consensus of opinion in this connection seems to be that the birds are controlled largely by what we in our ignorance term instinct. The true beginning of the migration seems to be in the fall, when the birds are driven from their homes by cold or, perhaps more accurately in most cases, by scarcity of food. This, however, is not the whole story, since many species start southward before cold weather approaches and while food is yet abundant. Then, too, crippled individuals have been known to survive the winter in regions from which their summer companions have departed. Instinct, therefore, plays a part in even the fall migration, where at first glance sufficient physical reasons may seemingly be claimed for it. During the spring migration the birds are moved by a strong impulse to regain their breeding-grounds. Each species seems to have adapted itself to certain conditions of temperature, food, etc., through long ages of development, and acquired a subtle faculty of regaining the environment to which it is best adapted, as soon as the adverse conditions that caused it to leave its home are ameliorated. How a particular bird is enabled to return to the nest it built the year previous is not known. The study of the homing instinct of pigeons assists in this direction, however, and suggests that birds are endowed with something answering to a sixth sense--that is, a sense of direction or of orientation. _Spring-time Music._--The northward-flowing tide of life each spring brings to the temperate zone of North America a marvellous change not only in colour and movements, but in sound. This is the season of bird courtship and more than usual happiness among the feathered millions. From shore to shore of the continent a chorus more seductive than sirens' songs pulsates on the breezes.