View additional resources, online and in print, for NATURE's "Flight School."

Joseph Duff is one of the leaders of Operation Migration, a nonprofit organization that is using aircraft to restore migrating populations of whooping cranes.

Each spring and fall billions of birds hit the "flyways," atmospheric roads for annual migrations, which can stretch thousands of miles.

For many animals, the urge to move when the days change length and temperatures vary is programmed into their genes.

View additional resources, online and in print, for NATURE's "Earth Navigators."

Animals ranging from giant humpback whales to tiny eels make massive journeys in search of food and mates.

NATURE follows the world's most dauntless creatures in their epic migrations in "Earth Navigators."

While the bear gatherings are extraordinary, so is the story of how the fish find their way back to their home rivers each year.

Every fall, thousands of monarch butterflies fly west to their wintering grounds in California and Mexico, covering the trees with their bright shimmering wings.