Some common migratory birds include hummingbirds, blue jays, orioles, thrushes and Arctic terns. Ornithologists classify migratory birds into three categories: short-distance, middle-distance and long-distance migrants. The motivation to migrate is one of the main deciding factors in the type of migration a species undertakes.
For example, short-distance migrants, such as the bridled titmouse and the blue grouse, are generally permanent residents of the range they inhabit but exhibit migratory tendencies within specific areas of that range or from higher to lower elevations. The majority of this type migrate in search of more abundant food sources.
The motivation to migrate of middle- and long-distance migrants, such as the eastern bluebird, magnolia warbler, whooping crane and the blue-winged teal, is often more complex than that of short-term migrants. Triggers include the search for food sources, breeding and nesting necessities, changes in the weather, genetic makeup and a host of other elements.
Long-range migrants such as raptors, vultures and shorebirds breed in the north and winter in the tropics. The Arctic tern migrates from its breeding grounds in northern Canada to its home in Antarctica, a 24,000-mile journey roundtrip. While Arctic terns commonly follow two pathways on this huge journey, other migratory behavior is not as consistent. Even subspecies within a migratory species may follow very different patterns and employ different navigation tactics.