Question: How do geese find their way back after they fly south?
- S.S., Peabody, Mass.Answer: Geese - and most of North America's nearly 800 bird species - migrate regularly to follow the food supply as the seasons change. Many species can migrate incredibly long distances.
Lesser snow geese that summer in Siberia, for instance, can winter in California's Central Valley. Pintails from Alaska have been found in Guatemala - nearly 5,000 miles away, according to the comprehensive book, "Ducks, Geese and Swans of North America," by waterfowl biologist Frank C. Bellrose. There's even evidence, Bellrose says, that blue-winged teals from New England fly non-stop over the Atlantic in grueling journeys that can top 2,000 miles.
Migrating birds can fly from a few feet above sea level to altitudes of over 20,000 feet, although most fly between 3,000 and 10,000 feet, says John Takekawa, a biologist with the United States Geological Survey who uses satellite radio collars to study the migration of snow geese.
Migrating birds often remain faithful to their breeding area and return to the same spot as adults to lay eggs and fledge young.
So how do they find their way back?
Birds make extensive use of landmarks that are visible from the air. "Most likely it's rivers and mountain ranges," Takekawa says. "We see them follow rivers."
Some studies have indicated that birds can overshoot their destination when flying on overcast nights with low-hanging clouds - when they can't see familiar cues on the ground.
Migrating birds may also use a variety of other cues, including the sun and the stars, Bellrose says. But many birds find their way even when flying between layers of clouds that block views of both ground and sky. They may be using Earth's magnetic field as a guide.
Birds also learn routes from their parents.
"Young birds are probably following older birds," Takekawa says. "Young birds go south with their family and learn the route. The first trip they're learning. The second trip they're getting it down. The third or fourth trip, they're on their own."
You can follow snow geese as they migrate - and even see the field notes of Takekawa and his colleagues - at the National Audubon Society's "wild wings" Web site: (http://north.audubon.org).