Toads in Turmoil.

Up to one third of the nation's amphibians --frogs, toads, and salamanders--have vanished in part of their native habitats, claims the U.S. Geological Survey. "Some frogs, for example, have totally disappeared from Colorado's most pristine forest areas," says Michael Alexander, a climatologist (climate scientist) at the National Oceanic and Atmospheric Administration. Alexander studies frogs in Rocky Mountain National Park--the site of thousands of mysterious amphibian deaths over the last two decades.

The possible culprit: an unidentified skin fungus (type of organism like mold or mildew). Since amphibians absorb oxygen through their skin to breathe, a fungal infection can suffocate them. Colorado's leopard frogs and boreal toads may be victims of fungal-related die-offs: 70 to 95 percent of sites in Colorado, once abundant with boreal toads are now entirely devoid of them.

Though the fungus origin is unknown, some scientists think amphibians may be more vulnerable to illnesses because of air and water pollution, and exposure to excess ultraviolet light due to ozone depletion, the loss of Earth's protective layer of atmosphere. Since scientists consider amphibians indicator species, highly sensitive to environmental change, their decline may be a grim sign for the future of other animals.