There is huge variation in the migratory habits of North American birds. Meadowlarks, song sparrows, and bluejays make such short migrations that specific locations appear to have resident birds all year long, even though individual birds actually move in and replace others of their kind who have also moved. Some oceanic birds migrate inland and then back to the ocean. Some mountainous species migrate by elevation. In broad, simple terms, though, most migratory birds fly north in the spring to nest and then south in the fall to winter, either in the southern United States, or in Central or South America.
Some species fly only at night.
Wind direction and currents, weather, topography, and appropriate stopover habitats dictate flight patterns. Curiously, few northbound birds follow an identical route going south as going north. The bird's system of built-in navigation is not entirely understood by biologists. Techniques among species vary, but they apparently include combinations of celestial navigation, visual landscape clues, the setting and rising sun, sense of smell, and the Earth's magnetic fields. And a miraculous genetic coding that comes at birth.