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Figure 3.—Migration of the cliff swallow, a day migrant that instead of flying across the Caribbean Sea as does the blackpolled warbler (see fig. 6), follows around the coast of Central America, where food is readily obtained. (See p. 25.)

An interesting comparison of the flights of day and night migrants may be made through a consideration of the spring migrations of the blackpolled warbler and the cliff swallow. Both spend the winter in South America, at which season they are neighbors. But when the impulse comes to start northward toward their respective breeding grounds, the warblers strike straight across the Caribbean Sea to Florida (fig. 6), while the swallows begin their journey by a westward flight of several hundred miles to Panama (fig. 3.). Thence they move leisurely along the western shore of the Caribbean Sea to Mexico, and continuing to avoid a long trip over water, they go completely around the western end of the Gulf of Mexico. This circuitous route adds more than 2,000 miles to the journey of the swallows that nest in Nova Scotia. The question may be asked: "Why should the swallow select a route so much longer and more roundabout than that taken by the blackpolled warbler?" The simple explanation is that the swallow is a day migrant while the warbler travels at night. The migration of the warbler is made up of a series of long, nocturnal flights, alternated with days of rest and feeding in favorable localities. The swallow, on the other hand, starts its migration several weeks earlier and catches each day's ration of flying insects during a few hours of aerial evolutions, which at the same time carry it slowly in the proper direction. Flying along the insect-teeming shores of the Gulf of Mexico, the 2,000 extra miles that are added to the migration route are but a fraction of the distance that these birds cover in pursuit of their daily food.