SEATTLE--Evidence is piling up that global warming is affecting birds. Now, a study suggests that some woodpeckers within a population may adjust better to the rising mercury than others. But researchers say it's difficult to predict what these and other findings will mean for bird populations.
In the pine forests of North Carolina, Jeffrey Walters of Virginia Polytechnic Institute and State University in Blacksburg has been studying red-cockaded woodpeckers for 2 decades, gathering data on breeding behavior and reproductive success from hundreds of tagged individuals. At the meeting of the American Ornithologists' Union and the Society of Canadian Ornithologists here on 18 August, Walters presented work done with Karin Schiegg and others, showing that over the last 19 years, female woodpeckers have been laying their eggs 4 days earlier in response to warmer inland temperatures and increased rainfall on the coast. The adjustment was made by individual birds throughout their lifetimes. Because red-cockaded woodpeckers that breed earlier generally raise more young, the team thinks it's beneficial for a bird to breed as early as the climate will allow.
Some woodpeckers couldn't adapt, however. Novice breeders and females breeding with a new mate failed to adjust their egg-laying, suggesting that birds need to be familiar with their mates to respond to environmental change. Also failing to shift were inbred birds. Biologists have long known that inbreeding reduces animals' abilities to deal with environmental challenges, but this is the first such demonstration with climate change, the researchers say. They add that species with small isolated populations, like the red-cockaded woodpecker, may have many inbred birds--and could have trouble adapting to climate change.
The new study adds to a growing but complex body of evidence about the effects of climate change on birds. While Walters thinks that breeding earlier is beneficial for woodpeckers, a study published earlier this year showed that for blue tits, it might mean food shortages (ScienceNOW, 30 March). "I'm not sure anyone's sure what it all means," says Todd Engstrom of Tall Timbers Research Station in Tallahassee, Florida. But "it's very obvious that birds are very good indicators of climate change," he says. "The pieces of evidence are really coming together now."
Walters's Avian Ecology Group at Virginia Polytechnic Institute and State University
Comprehensive bibliography on effects of climate change on species and ecosystems
More on the red-cockaded woodpecker, from the U.S. Fish and Wildlife Service