The Global Amphibian Decline:
Trends, Causes, and Challenges

Cascades frog (Rana cascadae)
photo by Frank Ely

Introduction

Global Trends
North America
Central and South America
Australia
Europe

Causes
Habitat Modification
Exotic Species
Acidification and Toxic Contiminants
Ultraviolet Radiation
Climate Change
Pathogens

Challenges

Bibliography

Links

Regional Trends: North America

The most systematic reports of amphibian declines have come from western North America, where most reports have concerned frogs of the genus Rana and true toads in the genus Bufo. The Wyoming toad (Bufo hemiophrys baxteri) began to decline in the 1970s and is considered extinct except for a single wild population found in 1987; no egg masses have been found in this population since 1991, indicating little or no recruitment of new individuals. The boreal toad (Bufo boreas boreas), once widely distributed and abundant in the southern Rocky Mountains, southeast Wyoming, and northern New Mexico, is declining throughout its range. The Vegas Valley leopard frog (Rana fisheri) is probably extinct, while the relict frog (Rana onca) is declining in Nevada and southwestern Utah. Northern leopard frogs (Rana pipiens) have declined throughout their range in the United States and Canada. The spotted frog (Rana petiosa) has declined in both the United States and Canada. The Tarahumara frog (Rana tarahumara) has disappeared in southeastern Arizona and the northern Sonora. The California red-legged frog (Rana aurora draytonii) was once the most common frog in California, but is now listed as an endangered species. The cascades frog (Rana cascadae, above) has declined in California and Oregon. Censuses also indicate that the tiger salamander (Ambystoma tigrinum) is declining in the Colorado Rockies.

Notably, all native frog and toad species in the Yosemite area of the California Sierra Nevada have experienced declines or losses of local populations over the last century. Such a decline in an entire frog fauna in a large, diverse region is unprecedented. The Yosemite toad (Bufo canorus) has declined throughout its range. The mountain yellow-legged frog (Rana muscosa) has disappeared from lower altitudes as well as from many high-elevation lakes and streams, going from being the most abundant species to one of the most rare. The Pacific treefrog (Hyla regilla) is relatively common and widespread throughout its range, though populations in the Yosemite area are faring poorly.