Frogs On The Verge Of Extinction

They predate the dinosaurs, but they appear to be nearin the same fate: Amphibians, which include frogs, toads and salamanders, are declining worlwide in alarming numbers.

Medicine & Science

October 18, 2004|By Dennis O'Brien | Dennis O'Brien,SUN STAFF

One of the oldest life forms on Earth is disappearing, and no one knows why.

The number of amphibians - a class of creature that predates the dinosaur and includes frogs, toads and salamanders - is declining across the world at astonishing rates.

Costa Rica's golden toad vanished from a pristine wildlife refuge in about three years. Fewer chorus frogs are singing in upstate New York, and the Mississippi gopher frog has all but disappeared from the Southeast.

There could be many reasons: climate change, habitat loss, man-made pollutants, and recently discovered diseases. But researchers acknowledge that they have no clear answers as to why so many extinctions are occurring worldwide - and at such alarming rates.

"There isn't any one angle, or one cause that we know of," said James Hanken, an amphibian expert at Harvard University. "We really don't know the reasons for all these declines."

There is more is at stake than the fate of some water-soaked croakers. Amphibians have been around for 350 million years. Living on water and land, they're among the most ecologically sensitive creatures on Earth. They're a major food source for birds, fish and mammals, and they gobble up disease-bearing insects. So their demise could be a signal that other wildlife is at risk.

"There's no question but that these creatures are the canaries in the coal mine," said Richard A. Seigel, chairman of the biology department at Towson University, who has studied frog populations throughout the United States.

Amphibian populations have not declined significantly in Maryland and nearby states. The wood frog, American toad, bullfrog and spring peeper thrive in area waterways, Seigel said. But with increased development and pollution threatening habitats, their populations might soon begin to drop.

"We know there's a problem, and we just wonder if maybe it's just a matter of time," he said.

A study published online last week by Science Express documents the severity of the problem worldwide. About a third of the 5,743 species of amphibians known to exist - about 1,856 - are threatened with extinction, the report says. By contrast, 12 percent of the world's bird species face a similar threat.

Researchers began documenting amphibians' losses in the 1970s, when they found the Wyoming toad and other amphibian populations declining in several Western states. Scientists have since reported declines of various species of frogs, toads and salamanders in Central and South America, Australia, China and other ecological hotspots.

Declining frog populations became a hot topic in the 1990s, with federal officials setting up a task force, launching a Web site and pumping millions of dollars into research.

"In the case of amphibians, there were a number of sources of the problem, and the concern was, what did it mean for the environment?" said William Brown, adviser to former Interior Secretary Bruce Babbitt.

But the study's authors say their report is the first that puts all the evidence together.

"For years, we knew there were more or less isolated losses of some species in some parts of the world, but no one was looking at this globally. It's only now that we know it's a big issue and a big problem," said Janice S. Chanson, an ecologist at the World Conservation Union and a co-author.

The report, due to be published in the journal Science in a few weeks, was co-written by researchers from the union, Conservation International and NatureServe, all conservation groups.

About 500 researchers in 60 countries participated in the three-year study. Experts counted frogs and toads on field trips and, in many cases, estimated populations based on calls recorded with microphones.

The study found that most threatened species are in the tropical regions that are host to most of the world's amphibians, such as Brazil, Colombia, Ecuador and Mexico. Since 1980, nine species of amphibians have been declared extinct, but another 113 have disappeared or almost disappeared, the report says.

"Things are not going well in a lot of places," Chanson said.

Losses are occurring across the spectrum of frogs, toads and salamanders. Frogs, with smooth moist skin and long thin legs, live mostly in water and hop away to escape predators. Toads are fatter, with shorter legs and rougher skin. They live on land, and many have poisonous skin to keep from being eaten. Salamanders have long tails, are generally smaller and hide under logs and leaves.

The authors blame some declines on habitat loss, pollution and activities such as frog hunting - frog hides are used for wallets in Asia, and their legs are a delicacy in many parts of the world. But almost half of the lost species are dying from "unidentified causes" because they disappear before they can be studied.

"These declines tend to be very rapid, and few of them have actually been observed taking place," the report says.

Some scientists say the best example of such a mysterious decline might be that of the Monteverde golden toad of Costa Rica.

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