Climate change increases the number of endangered species.
The buff-breasted sandpiper manages to fly from Alaska to Argentina each fall, but the sturdy little two-ounce shorebird is proving no match against man. Oil development in its breeding grounds in the arctic and the conversion of grasslands to soybean fields at its wintering grounds in South America are changing its takeoff and landing sites so radically that the sandpiper, after rebounding somewhat from near-extinction in the 1920s, is again on the decline. And it's in good company. Today the National Audubon Society and the American Bird Conservancy are issuing their WatchList 2007, a compendium of bird species in peril, and the buff-breasted sandpiper joins 177 other species in the continental United States plus 39 in Hawaii whose numbers have declined or are declining toward unsustainable levels. The number of threatened species is up 11 percent since the last watch list was issued in 2002.
The WatchList puts 59 continental and 39 Hawaiian birds on the "red list" of greatest concern, and 119 in the "yellow" category of populations that are seriously declining or already rare. As has been the case for decades, habitat loss, predation and invasive species are the chief culprits behind the decline. But now there is a new entrant on the list of threats: global warming.
Among the most imperiled species that regularly breed in the continental United States are the gunnison sage-grouse, a chickenlike resident of southwest Colorado and adjacent parts of Utah. Drought, which is worsening with global warming, as well as habitat loss and excessive grazing, have slashed its population to fewer than 5,000. The black-capped vireo is officially endangered, the victim of suburban development, conversion of scrubland to agriculture and parasitism by brown-headed cowbirds. Cowbirds lay their eggs in vireo nests, where their chicks out-compete vireo chicks for food brought back by parents.
Suburbanites who put out black-oil sunflower seeds for their local songbirds are small compensation for the threat that suburbanization itself poses to several species. The red-cockaded woodpecker, for instance, has seen its home in the Southeast's long-leaf pine forests converted to suburbs and farms, isolating populations and slashing its numbers.
Habitat loss and hunting have long led the list of threats to birds (and other species), but climate change has joined the list. The Kittlitz murrelet, for instance, breeds and feeds around Alaska's tidewater glaciers, which are retreating as the world warms. Drought and other consequences of climate change are threatening the survival of the lesser prairie-chicken of Kansas, Colorado, Oklahoma, New Mexico and Texas. The warming arctic is melting the habitat of the spectacled eider and making it easier for foxes, mink, gulls and jaegers to snatch chicks from their nests. In addition, the warming seas are altering the distribution of clams, a chief source of winter food for eiders.
Not surprisingly, the rise in sea levels due to global warming isn't helping shorebirds. The sharp-tailed sparrow, for instance, lives only in a narrow band of salt marsh along the Atlantic and Gulf coasts. As seas rise, its home shrinks. Global warming is also altering ocean circulation and the distribution of fish, mollusks and other bird foods, with the result that the Xantus's murrelet, for instance, which nests on islands off Southern California, and other coastal seabirds are imperiled due to food shortages.
Not all the news is grim. The status of some WatchList species has improved, with the population of the California condor having recovered from nine wild birds in 1987 (all of which were brought into captivity so they would not go extinct) to 305, thanks to captive breeding programs. Lead bullets still pose a threat, however, since the condor eats the remains of hunters' kills. There were only 16 whooping cranes in 1941, due to habitat loss and shooting, but a recovery plan focusing on captive breeding in Florida and Wisconsin under the Endangered Species Act has brought the population back over 200 individuals. (Though it didn't help matters that in 2004 hunters shot two whooping cranes in Kansas, mistaking them for sandhill cranes, which are legal to kill.) The piping plover has also benefited from the ESA, which has required protection of this shorebird's beachfront nesting grounds.