evidence to link pesticide use with amphibian decline
use, already considered a factor in the decline of the threatened
California red-legged frog, may also be affecting three additional
frog species, according to a new study being released this week.
California State University, Sacramento environmental studies professor
Carlos Davidson, who had previously linked pesticide use to reductions
in red-legged frog populations, says upwind agricultural use is
also associated with declines in the mountain yellow-legged frog,
the foothill yellow-legged frog and the Cascades frog. "It
strongly suggests wind-borne agrochemicals may be a factor,"
The findings are featured in the current issue of the journal Conservation
Davidson, along with colleagues Brad Schaffer of the Center for
Population Biology at the University of California, Davis, and Mark
Jennings of Rana Resources, studied the effects of four environmental
factors - windborne pesticide use, habitat destruction, UV-B radiation
and climate change on eight declining amphibian species.
control for regional factors, the study combined multiple species
with distinct ranges throughout California, including the California
red-legged frog, California tiger salamander, western spadefoot
toad, arroyo toad and Yosemite toad in addition to the mountain
yellow-legged frog, foothill yellow-legged frog and the Cascades
The researchers compared historic populations with recent survey
data and then analyzed the geographic patterns for possible causes
of the declines. The percentage of formerly occupied sites that
are now absent was high for all species,
from 33 percent absent in the tiger salamander to 83 percent absent
in the mountain yellow-legged frog.
Of the four factors, upwind agricultural land use - with the potential
for windborne pesticides - could be linked to the declines in all
four frog species. Sites that had seen declines had up to four times
more agricultural land use than sites where the species still exist.
Habitat destruction was found to be a factor in declines among tiger
salamanders and the spadefoot toads.
Concerns over sharp declines led the U.S. Fish and Wildlife Service
to add red-legged frogs to the threatened species list in 1996.
The Center for Biological Diversity is now suing the Environmental
Protection Agency for allegedly failing to consult with Fish and
Wildlife about the possible affect on the frogs when pesticides
Davidson is now looking at the association between historic pesticide
use and amphibian declines in California. He and Schaffer are also
studying the effects of low-doses of pesticides on amphibian susceptibility
Media assistance is available by contacting the CSUS public affairs
office at (916) 278-6156. Davidson can be reached at (916) 287-6063.