It was earlier thought that birds split their time between North America and the tropics of South America to avoid competition for food and mating partners while in warmer climates.
But new research points to the birds moving from the northern climates to avoid harsh winters.
Writing in the journal PNAS, lead author Ben Winger of the University of Chicago says his colleagues studied the evolutionary history and family trees of 823 types of American songbirds.
They found that most migrating species come from ancestors that originated in a temperate climate rather than in the tropics.
This indicates their migratory patterns began as a way to avoid winter’s chill.