The mountain yellow-legged frog has survived for thousands of years in lakes and streams carved by glaciers, living up to nine months under snow and ice and then emerging to issue its raspy chorus across the Sierra Nevada range.
But the frog's call is going silent as a mysterious fungus pushes it toward extinction.
"It's very dramatic," said Yosemite biologist Lara Rachowicz. "One year, you visit a lake and the population will seem fine. The next year you go back, you see a lot of dead frogs scattered along the bottom of the pond. In a couple years the population is gone."
There are about 650 populations left in Yosemite, Sequoia and Kings Canyon national parks, but most lakes have only one to five frogs — not enough to guarantee survival — and 85 percent are infected with the lethal fungus.
The frogs were once so thick that tadpoles frothed in shallow waters, and it was hard not to step on a frog on shore.
Their decline began with the artificial stocking of trout in Sierra lakes — first carried in buckets by mule and then dropped by plane — for sport fishing. The voracious predator pushed the frogs into isolated lakes.
The remaining frogs can't withstand the fungus and can't travel far enough in trout-infested streams to repopulate the depleted habitat.
The frog population has dropped by 10 percent a year for five years, Rachowicz said at a gathering last month of 24 experts trying to save the frog.
The chytrid fungus, linked to the extinction of amphibians from Australia to Costa Rica, grows on frog skin, making it hard to use their pores and regulate water intake. The frogs die of thirst in the water, Rachowicz said.
Despite the threat of extinction, the U.S. Fish and Wildlife Service lacks funds to make the frog an endangered species. Federal officials also questioned what good it would do, because the fungus isn't coming from agriculture or development that can be curbed.
"It's an act-of-God type thing," said Harry McQuillen, chief of the endangered species recovery branch of the agency's Sacramento office. "How do you deal with something that seems overwhelmingly out of your control?"
The fungus is frightening because it kills frogs quickly even in untouched habitats, scientists said.
His research offers the first solid clue to an international scientific mystery — the disappearance of as many as 112 amphibian species since 1980.
U.S. biologists will look at breeding the critters in captivity, which has not been done successfully. They may also re-establish frogs in areas where they've disappeared, and remove more nonnative trout from some high Sierra lakes. Trout removal has had promising results in Sequoia and Kings Canyon, but could prove unpopular with anglers.
"Recreational fishing is a long-standing, valid activity in the park, and we recognize that," said Steve Thompson, Yosemite's lead wildlife biologist. "But the park has a dual mission, to protect resources and provide for their enjoyment. If you don't protect the resources, it'll prevent the enjoyment."