"Declines of four...species were strongly associated with the amount of upwind agricultural land use, suggesting that wind-borne agrochemicals may be a factor," say Carlos Davidson of California State University, Sacramento; Brad Shaffer of the University of California, Davis; and Mark Jennings of Rana Resources in Davis, California, in the December issue of Conservation Biology.

Davidson and his colleagues studied the effects of four factors thought to play a role in amphibian declines (pesticide use, habitat destruction, UV-B radiation and climate change) on eight species that are declining in California (four frogs, two toads, one spadefoot toad and one salamander). To identify areas where each species used to live but no longer exists, the researchers compared historic distribution records with recent surveys.

Davidson and his colleagues found that of the factors considered, only habitat destruction and pesticides were linked to declines of the amphibians studied. Habitat destruction was based on the amount of urban and agricultural land use in a 3-mile radius around the site, and likely pesticide exposure was based on the amount of upwind agricultural land use.

Habitat destruction was linked to the declines of two species: sites that have lost the California tiger salamander and the Western spadefoot toad had 3 and 6 times more local urbanization, respectively, than sites where these species still live. The spadefoot toad depends on vernal pools, many of which have been destroyed by urbanization or conversion to agriculture.

Pesticides were linked to declines of all four frog species (the mountain yellow-legged frog, foothill yellow-legged frog, California red-legged frog and Cascades frog). Sites that have lost these frogs had abou
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Contact: Carlos Davidson
cdavidson@csus.edu
916-278-6063
Society for Conservation Biology
21-Nov-2002