For centuries people have marveled as some birds mysteriously disappear each fall. As late as the 16th century people thought birds hibernated! Rather than ending the mystery, the discovery of migration has prompted even more questions.
Many factors help birds migrate. Genetics may explain the direction, timing and distance of migration for some species. But others, like geese and cranes, learn migration routes through social contacts with family and other flock members.
Birds use landmarks like rivers, mountains and forests to orient themselves over familiar territory. The sun acts as a daytime compass, and birds are able to compensate for its movement to keep a straight course. On overcast days, at night, or over featureless oceans, birds use the stars and the earth’s magnetic field to guide them.
Many birds have heightened senses that may assist in navigating. Some birds have pressure sensors in their middle ear that can detect an approaching weather front. The eyes of other species are very sensitive. And some birds have heightened senses of smell and memory for those odors which help them find their way.
Why do birds migrate? Usually cold weather in the fall eliminates food sources, requiring birds to move where food is plentiful. Bird migration is a complex truly amazing phenomenon which continues to excite and puzzle backyard bird watchers and ornithologists alike!
One of the best places in Portland to see the fall migration is Sauvie Island. Ducks, geese, cranes and eagles will delight the eyes in numbers not seen anywhere else in the metro area. Don’t forget to take your binoculars!