If you've ever watched birds at a feeder, you've seen changes in how many birds feed from season to seasons and year to year. Do some of the long-term shifts reflect changes in the environment and climate? To find out, the Cornell Lab of Ornithology's Project FeederWatch is asking bird watchers for help.

FeederWatchers count the birds at their feeders each week and send the information to the lab. They've helped document unusual bird sightings, winter movements and shifting ranges of some bird species over the past 20 years. To see the effects of global climate change, scientists say they need new and veteran participants alike to help count birds.

"Being a FeederWatcher is easy and fun, and at the same time, helps generate the world's largest database on feeder-bird populations," says project leader David Bonter. "Since we started in 1987, nearly 40,000 people have submitted observations, adding up to well over 1.5 million checklists."

Some of the most dramatic changes revealed by data collected during two decades of Project FeederWatch may be related to changes in climate, he says.

"We're seeing hummingbirds turning up much farther north than usual during the winter," says Bonter. "Warblers and other insect-eaters are also lingering longer into the northern winter, possibly because of warmer temperatures. Bird count data gathered in the coming years will really help us focus on these trends and what might be causing them."

The 21st season of Project FeederWatch runs from Nov. 10 through April 4. All ages and skill levels are welcome. To learn more or to register, visit http://www.birds.cornell.edu or call toll-free (800) 843-2473.

- Cornell University