8/27/1999 629

AGRICULTURE LINKED TO RED-LEGGED FROG DECLINE IN CALIFORNIA

Global decline of amphibians has been attributed to everything from UV radiation to global warming. The first concrete evidence that agriculture may play a role in this decline was presented in June by Carlos Davidson of UC Davis at a Society for Conservation Biology meeting. Davidson and H. Bradley Shaffer, also of UC Davis, studied the case of the California red-legged frog, which was once found from the coast to the Sierra Nevada but today is restricted chiefly to the central coast. They looked for links between the frogs' decline at a given site and factors including UV radiation, global warming, urbanization, and agriculture.

Agriculture had the strongest link to the red-legged frog decline. Frogs were more likely to have died out at sites that were upwind of greater amounts of agriculture, suggesting that wind-borne agrochemicals may have caused the frogs' decline. Davidson and Shaffer determined the prevailing wind direction for each site and drew a 90-mile long triangle facing into the wind for each site. They found that in sites where red-legged frogs have died out, about 19% of this triangle was agricultural land. In contrast, for sites where red-legged frogs still survive today, only about 3% of the triangle was agricultural land.

Davidson cautions that while these findings are significant, they do not prove that agricultural chemicals are wiping out red-legged frogs. "It's a huge leap to say that the amounts of pesticides that get up to the Sierra Nevada kill frogs," he says. "But it's a pattern that suggests that we should look into the role of pesticides in frog declines further."