The Aptitude to fly,
Meadows of Majesty concedes
and easy Sweeps of Sky-
Emily Dickinson
Seasonal migrations are hazardous for the participants but necessary for species that require alternate areas for food and nesting. The triggers for this periodic travel can be the change in hours of daylight, variation in temperature, and the availability of food.
Methods of navigation probably depend on the position of the sun, moon and stars, the earth's magnetic field, landmarks, genetics and maybe even smell.
Cornell's Lab of Ornithology and the Audubon Society maintain a website (ebird) where visitors can see beautiful, animated occurrence maps of bird migrations.
