There are as many styles of migration as there are types of birds. Some birds migrate during the day while others fly at night. Some fly alone while others flock together. Some flocks are highly ordered while others are loose congregations.
Some birds travel at high altitudes while others fly low.
Some fly over water while others stay over land. Migration is one of the most widely studied areas of bird biology, yet it is still poorly understood. People have observed and noted migrations for centuries, yet we still have only a handful of theories about how birds accomplish such impressive flights each year. Migration seems to be triggered by a combination of shortening days and seasonal atmospheric changes, which allow cold fronts to carry frigid air on strong winds. As temperatures drop, insects and plants die while amphibians and rodents hibernate, causing food sources to become scarce.