What's Causing Bird and Amphibian Decline?

Cameron Walker
for National Geographic News
November 8, 2004

Species in the air and on the ground are in deep trouble, according to two recent studies tallying declines in bird and amphibian populations.

While many factors may be causing this, climate change could be behind amphibians' decline, while habitat loss is whittling away bird populations.

Nearly 1 in 3 of the 5,743 described amphibian species are in decline, according to survey results released last month. At least nine species have disappeared since 1980.

"It was much worse than we expected," said Simon Stuart, leader of the Global Amphibian Assessment organized by the World Conservation Union (IUCN), Conservation International, and the Virginia-based conservation nonprofit NatureServe.

"The evidence of amphibian decline is getting clearer and clearer," said Stuart Pimm, a conservation biologist at Duke University in Durham, North Carolina. In a group of 435 species suffering rapid declines, nearly half face neither vanishing habitat nor overexploitation. "It's beyond the normal cause, habitat destruction," Pimm said.

Birds were added to the lineup of species in trouble when the U.S. National Audubon Society released its first State of the Birds report, also last month, documenting the decline of nearly 30 percent of North America's birds.

From past bird surveys, researchers had known the extent of the problem, said Greg Butcher, director of bird conservation for the Audubon Society. "This is just a way of laying it out in black and white," said Butcher, who led the State of the Birds project.

Even though scientists have identified only one-tenth of the estimated 15 million species of birds worldwide, Pimm said, it's clear that species have gone missing. "There's a bunch of things that just aren't there anymore," he said.

Amphibians in Trouble

The amphibian study identified a group of species that is in decline for no readily obvious reason. These "enigmatic decline" species may be suffering from a combination of infectious disease and a changing climate, said Stuart, the amphibian study leader.

Amphibians have extremely thin skin, which makes them sensitive to slight changes in temperature, humidity, and air and water quality. It's also made them highly susceptible to chytridiomycosis, a fungal disease that appeared in the last two decades, first in Australia and Central America. The fungus has now spread to amphibians worldwide, and at least eight species have likely vanished as a result; an additional 113 species have not been found in the wild in recent years and may also have disappeared.

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