One of the most amazing feats in all of nature is a bird’s ability to find its way across continents without any apparent training or help.
Take a hen wood duck, for example, that is hatched in a tree cavity or birdhouse in Wisconsin, grows up on nearby water, flies to a southern state to winter, selects a mate, and then leads that mate back to Wisconsin the following spring to breed. How does she find the very nesting cavity in which she was hatched 10 months earlier?
Perhaps even more amazing is the flight of the hummingbird. A baby broad-tailed hummingbird hatches in a Colorado spruce nest in June, grows up in the surrounding envirnment, and then flies, alone, to South America for the winter. This baby bird is not led on this remarkable journey by its parents, because the parents leave Colorado before the youngsters. Apparently, a genetic code tells it when to migrate, where to fly, where to spend the winter in South America, and when and how to return to Colorado the following spring to raise its own family.
Virtually all migratory birds are programmed to migrate when the amount of daylight decreases to a certain point in the fall, and increases to a certain point in the spring. But the haunting question remains, how do birds of the year—babies just hatched a few weeks or months earlier—know where to fly, thousands of miles away, and how to come home in the spring?
-- George H. Harrison