The results, from the most comprehensive inventory ever done of North American birds, point to ecosystems in disarray because of habitat loss and other factors that have yet to be pinned down, researchers say. Yet ecologist Paul Ehrlich at Stanford University in Palo Alto, California, who has been warning about shrinking plant and animal populations for decades, sees some hope in this new jolt of bad news: "It might stir needed action in light of the public interest in our feathered friends."
In past decades, Ehrlich and others have documented the decline of particular bird groups, including migratory songbirds. But 5 years ago, Rosenberg; Peter Marra, a conservation biologist now at Georgetown University in Washington, D.C.; and their colleagues decided to take a broader look at what is happening in North America's skies. They first turned to the North American Breeding Bird Survey, an annual spring census carried out by volunteers across Canada and the United States, which has amassed decades of data about 420 bird species. The team also drew on the Audubon Christmas Bird Count for data on about 55 species found in boreal forests and the Arctic tundra, and on the International Shorebird Survey for trends in shorebirds such as sandpipers and plovers. Aerial surveys of water bodies, swamps, and marshes filled out the picture for waterfowl. All together, they studied 529 bird species, about three-quarters of all species in North America, accounting for more than 90% of the entire bird population.