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Amphibian Declines Driven by Complex Causes

Producer - Vince Patton
Videographers - Michael Bendixen, Todd Sonflieth, Nicholas Fisher, Frank Swanson
Editor - Michael Bendixen

A tadpole live in a tank in a lab at Oregon State University

A tadpole live in a tank in a lab at Oregon State University


Only one group of animals on the planet can start life as eggs floating in little more than jelly, hatch into swimmers entirely underwater, then completely morph their bodies to grow legs and ultimately crawl out to live on land. Amphibians’ ability to adapt may account for some of the longest-surviving species across Earth’s history.

However, adaptation has met its limits. For those who study amphibians, there has been one steady constant for the last two decades; in many locations they’re getting harder to find.

Today, the decline of amphibians is accepted fact. Twenty years ago that was not the case.

Two scientists, working independently, appeared on Oregon Field Guide in 1993 to sound the alarm that amphibians were disappearing around the globe.

Today, if they felt boastful, they’d be justified in saying, “I told you so.”

“In 1993 we didn’t know exactly what was going on,” says Professor Andrew Blaustein of Oregon State University’s zoology department. “It was still controversial to say that amphibian populations were in decline. We were just trying to figure out whether they were in decline. We thought they were.”

Marc Hayes, a senior research scientist with the Washington Department of Fish & Wildlife (WADFW), says, “It took awhile for things to get rolling, but the really positive thing is that many people are paying attention now.”

Two decades of research by Hayes and Blaustein has shown no easy answers as to why amphibian numbers have plummeted.

Blaustein made headlines in the early ’90s with his conclusions that ultraviolet radiation affected survival of some frogs. Lesser noticed were his findings about the same time that a water mold also affected many amphibians.

Oregon spotted frogs have disappeared from nearly 90 percent of their historic range.

Oregon spotted frogs have disappeared from nearly 90 percent of their historic range.

Vince Patton/OPB

“People love simple answers,” Blaustein says. “I don’t think it’s a simple answer why amphibian populations decline.Everybody always has their favorite hypothesis.”

In addition to UV radiation and water mold, Blaustein’s team of graduate students have looked for the chytrid fungus which has also been linked to frog die-offs.

He sends his students to places like Lost Lake, an alpine getaway just off Santiam Pass in Oregon’s central Cascades. Western toad populations are about half what they were 20 years ago at the lake, but still reasonably easy to catch. Equipped with sterile gloves and cotton swabs appropriate to a medical clinic, the budding scientists catch toads and rub the swabs up and down the toads’ bellies and legs.

Later tests in the lab reveal the chytrid fungus is present not only at Lost Lake, but at every lake Blaustein’s team has sampled.

Blaustein says, “The species that we look at, all of them tend to have a really different response to this fungus. So we have some species in the lab that die really, really quickly. Some species that don’t die at all.”

Unfriendly Neighbors

Bullfrogs are not native to the Northwest and frequently drive out native amphibians from their historic habitats.

Bullfrogs are not native to the Northwest and frequently drive out native amphibians from their historic habitats.

Vince Patton/OPB

WADFW’s Hayes supervises another avenue of research that investigates how much aggressive bullfrogs are to blame for the demise of frogs. He says Oregon spotted frogs have disappeared from nearly 90 percent of their historic range.

Yet one small group of spotted frogs bucks that trend. At Conboy Lake National Wildlife Refuge in southwest Washington, spotted frogs appear to live harmoniously with the larger, and usually predatory, bullfrogs.

“It really stuck out as the odd place,” says Hayes. He’s guiding Portland State University graduate student Kyle Tidwell who’s found that spotted frogs at Conboy Lake have found the best survival tactic is to just stand still.

When a predator dives from above, like a bird, the frogs jump away fast.

But if they approach from the side as a bullfrog would, even an animal as large as Tidwell himself, the frog just stands still. Tidwell often can wade slowly right up to the spotted frogs with his arm outstretched while the frog simply remains frozen in place.

“If you are a prey item for a bullfrog, it’s a good career move to remain still,” says Tidwell. “A bullfrog won’t see you. He won’t eat you. A theory that I have is that these spotted frogs here at Conboy Lake may be adapted to not moving and are thus not seen by the bullfrogs.”

So are big, bad bullfrogs getting a bad rap?

Tidwell says, “It is unclear as of yet.”

In addition to bullfrogs,  disease, mold, UV radiation and pesticides, Hayes and Blaustein agree that humans pose the greatest risk when they continue to bulldoze frogs from their homes in the name of development.

Says Blaustein, “The major problem is habitat alteration. Habitat destruction. We’re destroying their habits.”

Hayes adds, “If we’ve got things going on with frogs, we should be concerned about the general condition of habitat for humans as well.”

In 1993, when Oregon Field Guide first met him, Hayes was predicting that spotted frogs would soon be added to the endangered species list. 20 years later it appears that is about to finally happen.

“I think it’s a critically important step,” says Hayes. “Most of the endangered species acts at the state level don’t have an enormous amount of strength and when it steps up to a federal situation, it increases the attention on the species and help for the species enormously.”

A recent study from the U.S. Geological Survey says that in another 20 years, frogs could disappear entirely from half of the places they live in the United States.

WEB EXTRA: Toad With Fifth Leg

20 years of research confirms amphibians are still declining and the causes are complex.

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Most Recent Broadcast: October 31, 2013