for National Geographic News
A quarter of all bird species in the United States have declined in population since the 1970s, according to a report issued by the National Audubon Society.
Of more than 800 native U.S. bird species, 201 are included on the group's Watchlist 2000.
Frank Gill, Audubon's chief ornithologist, said the report "is the most comprehensive assessment so far of how American birds are declining."
The report indicates that some birds, such as the California thrasher (Toxostoma redivivum) and the southeast's painted bunting (Passerina ciris), have experienced population free-falls of 50 percent or more over the past three decades.
The population decline has been as high as 70 percent for the cerulean warbler (Denroiica cerulea), found across the eastern United States and especially in Western Virginia, and 80 percent for Henslow's sparrow (Ammaodramus henslowii), which is found in the Midwest.
Audubon issues the report periodically to help guide the allocation of conservation resources, especially for bird species that are seriously declining in population or facing threats such as major habitat loss but are not yet listed as threatened or endangered by the federal government.
Watchlist 2000 includes more than twice as many bird species as those federally designated as endangered or threatened.
The new figure is also twice as many bird species as were listed in the last comparable report by Audubon, which was issued in 1996.
The substantial increase can be accounted for in part by a broader survey range—Watchlist 2000 includes birds of Hawaii and Puerto Rico as well as the continental United States—and the use of a slightly different method for assessing the status of birds in the latest report.
In a population trend representative of many Hawaiian birds, the report says the akikiki (Oreomystis bairdi), a type of honey creeper on the island of Kauai, has declined from about 7,000 in the 1970s to fewer than 1,000 today.
The declining bird populations reflect growing threats to many bird species resulting from habitat loss and fragmentation caused by development and other human activities. Other contributing factors include depleted food sources, the impacts of pollution, incursions of non-native species—particularly on Hawaii—and diseases such as the West Nile virus.
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