I once spent an entire summer
catching frogs. Most people, I gather, do this in elementary
school: I was in my early 20s, with a supposedly marketable college
degree. I guess I should have done something a little, well, more
mature.
But I had an excuse. I’d been hired by the
U.S. Geological Survey to spend several months wading through the
lakes and streams of the northern Sierra Nevada. I set out each
morning with my work partner, waders and butterfly nets in tow, and
we caught, weighed, recorded and released every slippery frog, toad
and salamander we could find.
During those long summer
days, we tromped through miles of mud and thickets of weeds, got
lost, got frustrated, and, along the way, saw some of the loveliest
spots in the Sierra. We even got paid. At the time, I
couldn’t have asked for a better job.
Ultimately,
though, ours was a tragic task. The stacks of data sheets we mailed
to our boss each week told a tiny part of a global tale, and the
story wasn’t a good one. Throughout the world, many species
of amphibians are in dramatic decline, and those in the mountains
we surveyed were no exception to the trend.
Our boss,
herpetologist Gary Fellers, had already documented what he called a
“collapse” of frog populations in the Yosemite area: Over the
previous century, he and a colleague had found, most native frogs
and toads in and around the park had declined, and one species had
disappeared entirely. Fellers had then begun an ambitious statewide
survey of frogs and other amphibians throughout California; by the
time I and my fellow fieldworkers played our modest part in the
survey in the mid-1990s, he’d found that the situation
throughout the state was similarly grim.
The passage of
time hasn’t improved the outlook for the world’s
amphibians. A little over a year ago, in 2004, a global assessment
of frog, toad, and salamander populations showed that nearly a
third of known amphibian populations are in danger of extinction.
Theories for the global decline have abounded for
decades, and clues continue to crop up, but proof is frustratingly
scarce. Are scientists witnessing the effects of pesticides and
herbicides? Habitat loss? Exotic predators? Ultraviolet radiation?
Disease? Global warming? The only thing most observers can agree on
is that the problem isn’t simple: More than one factor is
likely to blame.
Last week, a study in the journal Nature
presented evidence for an ominous new argument. Researchers looked
at amphibian survey records from about 50 different sites in
Central and South America, charting the timing of extinction for
about 70 different species of harlequin frogs. They found that
these disappearances occurred in lockstep with warming global
temperatures.
The biologists argue that warming
temperatures created clouds, which — ironically —
cooled temperatures on the ground in some places, making conditions
more favorable to a fatal fungus and hurrying the frogs’
journey to extinction.
“Disease is the bullet killing
frogs, but climate change is pulling the trigger,” ecologist Alan
Pounds, an author of the study, told the journal. The casualties
could be widespread, since the disease in question — known as
chytrid fungus— already bedevils frogs in many other regions
of the world, including North America.
This finding
doesn’t settle the scientific debate. It’s still likely
that a whole host of factors are causing amphibian declines, with
different causes leading the way in different places. But the study
makes a powerful case that global warming influences disease
outbreaks, and, in turn, leads to species extinctions.
I
know: This is just More Bad News. You’ve heard enough to last
a lifetime. But this is bad news worth knowing, and not only if you
happen to like frogs. Biologists have long argued that amphibians,
with their delicate, porous skins, are the proverbial canaries in
the coal mine, the species most sensitive to global environmental
change. What happens to them could, down the road, happen to us,
and the sooner we can tease apart the reasons, the more time we
have to foresee and head off the consequences.
So in an
age when ecologists, and other people who keep an eye on the
natural world, are often outshone by their colleagues in more
glamorous scientific fields, it’s worth remembering that
humble observation can yield some very useful information. The
world is changing in ways we can’t imagine; we need a lot of
reliable witnesses.
I’ll bet that the legions of
footloose young biologists who survey frogs in Latin America also
love their long seasons in the forest, and are often saddened by
what they find. Now they, and we, have at least one explanation.
Michelle Nijhuis is a contributor to Writers on
the Range, a service of High Country
News(hcn.org). She is a free lance writer in Paonia,
Colorado.
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