Migration is an interesting phenomanom and no one knows for sure how avian migration started, although several theories have been presented. Most smaller birds migrate at night and rest and forage during the day. For some birds the migration path in the fall is different from the migration path in the spring.

Some birds migrate only short distances, sometimes moving from higher mountain summer homes to lower elevations within the same mountain range. In general, males do not migrate as far south as do females and young birds. This may be to allow them to return sooner each spring to start setting up and protecting their territories. Another theory is that their generally larger size allows the males to tolerate colder weather better.

Birds do exhibit amazing feats of endurance during migration.

Clark's Nutcracker cannot compete with some of the champion migrators. It may move only a few miles from its high-elevation summer home in the Sierras or the Rockies to the lower elevations in the same mountain range.

The ruby-throated hummingbird migrates non-stop across the Gulf of Mexico twice each year.

Some studies indicate that the blackpole warbler migrates south on a non-stop over-ocean route from southeast Canada and northeastern United States to their wintering grounds in South America. In the spring they take a more leisurely overland route back north.

For pure distance, the Arctic tern is the unrivaled champion. It can travel over 11, 000 miles each year from its summer home in the Arctic to winter residence in southern South America and Antarctica.