SPECIAL TO THE WASHINGTON POST
Monday, July 6, 1998 ; Page A03
For a long time, biologists literally could not believe
their eyes. It appeared that frogs and other amphibians were disappearing around the
world. But findings from several "hot spots" during the past year have persuaded
most scientists that the declines are indeed real.
"I think we're close to consensus now," said David Wake of the University of
California at Berkeley.
No one knows how many of the world's approximately 4,000 amphibian species may be
affected, and some areas rich in amphibian life -- notably Mexico and Africa -- have yet
to be evaluated. There are also vexing inconsistencies. Some species continue to thrive in
highly polluted, densely populated areas, while other populations crash in faraway places
side-by-side with species that are apparently unperturbed.
Nor do scientists yet have conclusive proof as to what may be causing any of the
declines. But there are four prime suspects: increasing ultraviolet radiation resulting
from ozone depletion, global climate change, pesticides and new diseases -- including a
recently discovered skin infection caused by a class of aquatic fungi not previously known
to affect vertebrates.
Scientists are concerned by amphibian declines for several reasons. Sometimes described
as sensitive "sentinels" because of their permeable skin, variable diets and a
life cycle that is partly aquatic and partly terrestrial, amphibians are without question
vulnerable to environmental insult.
Scientists have long known that habitat loss through human encroachment -- road
building, suburban sprawl, logging, agriculture, mining and fisheries management practices
-- is the leading cause of amphibian disappearance.
But beginning in the late 1970s, field herpetologists started noticing that amphibians
were becoming less abundant even in areas that seemed unaffected by human activity. The
mysterious losses from supposedly pristine habitats continued through the 1980s, a decade
that produced several extinctions, including the disappearance of the rare and beautiful
golden toad, which vanished shortly after it was discovered in a remote nature preserve
high in the mountains of Costa Rica. Other significant declines were reported from mainly
mountainous regions in Australia, much of Central America, parts of South America and in
the western United States and Canada.
But many scientists remained dubious. Through the mid-1990s, the scientific literature
contained more sniping than hard data. Skeptics, who saw the decline reports as alarmist,
argued that amphibian populations have such large natural fluctuations that no short-term
study could show a long-term trend. And they pointed out that the historical prevalence of
amphibians was largely unknown in most places.
But the evidence for widespread, unexplained declines mounted.
J. Alan Pounds and his colleagues in Costa Rica answered many of the skeptics late last
year with a statistical study of amphibian declines in the same mountain region that was
formerly home to the golden toad. Pounds's five-year survey showed that natural population
fluctuations could not explain the disappearance of 20 species of frogs and toads -- about
40 percent of the local total.
This spring, researcher Karen Lips reported still more amphibian declines in highland
regions of Costa Rica and Panama. Lips established a correlation between more aquatic
species and the probability of decline -- a finding that she said argues for disease or
chemical contamination as probable causes. Lips's work attracted attention for an
additional observation: She actually found large numbers of dead and dying frogs in the
jungle, in itself a startling finding.
"No dead or disabled frog can last long in the rain forest," Wake said.
"Finding any at all suggests to me that there must have been many, many more that
were not seen."
Necropsies performed on frogs recovered by Lips showed their skin was infected by a
parasitic fungus called a chytrid, which researchers now believe may be associated with
amphibian declines in Australia and Central America. Chytrid fungi, which also have
infected captive amphibians in several zoos, are believed to impair respiration because
many frogs and toads breathe through their skins. But it remains unclear whether the
fungus is the primary cause of death or a secondary effect of some other environmental
In California, Gary Fellers of the U.S. Geological Survey documented significant
declines in several frog and toad species in seemingly pristine areas along the spine of
the Sierra Nevada Mountains, including inside the protected confines of Yosemite National
Park, where amphibian records go back 75 years.
Fellers's work, which is being done under arduous, high-altitude conditions at 4,000
remote sites, is one of the most ambitious monitoring efforts underway anywhere. What
alarms scientists most about his preliminary findings is that the declines are all
occurring on the western slopes of the mountains -- the side facing California's heavily
agricultural central valley. Fellers believes pesticides atmospherically transported to
the mountains are a likely cause of the declines.
David Green, a herpetologist at McGill University in Montreal, at first suspected at
least some initial reports reflected only temporary local shifts in amphibian populations
and not larger changes. Now, he said, he is surprised and distressed by the complete
disappearance of the leopard frog from British Columbia.
The leopard frog is one of perhaps 10 species that Green now believes are in decline in
his country, where he heads the endangered species program. "And this is happening in
Canada," Green said, "which for the most part is pristine compared to the
At a world herpetology conference last summer in Prague, Wake and George Rabb, longtime
head of the international Species Survival Commission, decided to seek federal assistance
in creating a more centralized U.S. research effort.
Interior Secretary Bruce Babbitt last March requested a briefing by scientists studying
amphibian population declines as well as the outbreak of leg deformities occurring in
frogs and toads across the United States and Canada. "What these scientists told
me," Babbitt said, "hit like a flash of light in the night. They illuminated a
landscape of potential extinction that extends all the way around the world."
Babbitt arranged a second briefing in May for himself, Health and Human Services
Secretary Donna E. Shalala and Environmental Protection Agency Administrator Carol M.
Browner. The group, which also included Neal Lane, then of the National Science
Foundation, and Kathleen A. McGinty, chair of the White House Council on Environmental
Quality, agreed that it didn't want to create a big "Apollo Mission" type of
program, but recognized that there was a pressing need for centralized coordination of the
many scientists and research programs involved, Babbitt said.
Wake said the comparison some people have made between amphibians and the canaries that
once warned coal miners of danger isn't quite right. "If a canary died," Wake
said, "the miners got out of the mine. We don't have that option. We don't have any
place to go."
Cutline: Harlequin frog, Atelopus varius, from Panama
Leopard frog, Rana pipiens, disappeared from British Columbia
IMAGE SOURCES: U.S. Geological Survey; University of Michigan
Articles appear as they were originally printed in The Washington Post and may not
include subsequent corrections.