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Airdate: Sep 23, 1999
Scientist: Scott Weidensaul


What if the complex routes of migrating birds began with a simple wrong turn?

This season, literally billions of birds will migrate in search of a winter habitat with an abundance of food. These are ancient journeys which may have begun with a simple wrong turn. I'm Jim Metzner, and this is the Pulse of the Planet, presented by the American Museum of Natural History.

"There's a lot of controversy about how migration developed, and a lot of competing theories. It probably is a mixture of competition and climate and food availability. And probably partly just accident."

Scott Weidensaul is author of Living on the Wind, a book about bird migration. He tells us that the changing migration of one bird- the Rufus hummingbird- is offering scientists an example of evolution in action.

"Rufus hummingbirds, from the west coast normally migrate down into the highlands of central Mexico, but a certain percentage of them are born with a faulty sense of orientation and instead of flying south into Mexico, they sort of veer off at a 30 degree angle and wind up in the southeast US. Now if they did that 200 years ago, when Alabama and Georgia were covered with thick forest, they would have starved to death in the winter. But now they end up in a place like Atlanta, or Birmingham, where people have flowers through the winter and a mild winter, where people have hummingbird feeders. It's a great place for a hummingbird to be. And so they're surviving; they're returning home, they're breeding, they're passing that gene on and we're seeing what appears to be a rapid evolution of a new migratory route among these hummingbirds. And if it continues like this and if there is any kind of environmental degradation in Mexico that makes that a less desirable place for these birds to winter, you could actually see a replacement of one migratory route with another. Now that's speculation and we're a long way from that, but it's exciting to see this process in development. It's one of the first times we've been able to see this happen."

Pulse of the Planet is presented by the American Museum of Natural History. Additional funding for this series has been provided by the National Science Foundation. I'm Jim Metzner.