Without the influence of humans, the expected extinction rate for birds would be roughly one species per century, according to Stuart Pimm, professor of conservation ecology at Duke University's Nicholas School of the Environment and Earth Sciences, who is one of the report's principal authors.
"What our study does, for the first time, is provide a well-justified and careful estimate of how much faster bird species are going extinct now than they did before humans began altering their environments," said Pimm, whose research group pioneered the approach of estimating extinction rates on a per-year basis.
"Extinction rates for birds are hugely important, because people really care about birds," he said. "People enjoy them, and bird watching is a big industry. So we know the rates of bird extinctions better than the rates for other groups of species."
"Habitat destruction, selective hunting, invasive alien species and global warming are all affecting natural populations of plants and animals adversely," added Peter Raven, president of the Missouri Botanical Garden, who is co-principal author of the report and a longtime collaborator with Pimm.
The report will appear in the online edition of the Proceedings of the National Academy of Sciences during the week of July 3-7, 2006. Other authors are Alan Peterson, a physician in Walla Walla, Wash., and Paul Ehrlich and Cagan Sekercioglu, conservation biologists at Stanford University.
The researchers calculated that since 1500 -- the beginning of the major period when Europeans began exploring and colonizing large areas of the globe -- birds have been going extinct at a