Averting Extinction

Scientists are trying to save amphibians by bringing them into captivity.

By Alisa Opar

A decade ago, you might have spotted a Kihansi spray toad in its native Tanzania. But not today; the toads are believed to have gone extinct in the wild.

Now if you want to see one of the penny-sized, bright-yellow amphibians, your best bet is to visit the Bronx Zoo. The zoo’s population of toads is one of a growing number of radical measures to save amphibian species from being wiped off the face of the earth.

When scientists first discovered the species in 1996, thousands were thriving in wetlands alongside the waterfalls in the Kihansi River Gorge in south-central Tanzania. But by 2001, the toads had been pushed to the brink of extinction: The construction of a dam dried out the wetlands, and chytrid fungus—a disease that is decimating amphibian populations around the globe—was ravaging the animals. To save the species, zoo employees, in cooperation with the Tanzanian government, captured about 500 toads, and brought half of them to live in the Bronx (the rest were distributed in other zoos).

Today, the zoo’s 370 toads reside in seven climate-controlled aquariums filled with lush vegetation. They are kept in their own room, separate from other species, to limit the transmission of amphibian diseases.

“We’ll keep the animals here in captivity and propagate them until the time comes that they can be safely reintroduced into the wild,” says Jenny Pramuk, the zoo’s curator of herpetology.  

The Kihansi spray toad is not the only amphibian species that scientists are racing to save. In the last three decades, more than 120 species of frogs, toads, salamanders, and newts have gone extinct. Scientists estimate that one-third to one-half of the 6,000 or so amphibian species are currently threatened with extinction.

In an effort to bolster rapidly declining amphibian populations, hundreds of projects similar to the Kihansi spray toad program are in the works worldwide. The conservation efforts are coordinated by Amphibian Ark, an international conservation organization run by the World Conservation Union and the World Association of Zoos and Aquariums. The group is bringing endangered amphibians into captivity. In doing so, they hope to establish healthy captive colonies while scientists figure out how to protect the animals from chytrid fungus and other stressors and eventually reintroduce them safely into the wild.

The project aims to identify the 500 most endangered amphibian species, and to help establish 500 breeding programs in zoos across the globe that will each host a different type of amphibian. A top priority will be ensuring that species remain in or near their native countries.

“For some species, there are threats, particularly disease and climate change, that we simply don’t have the tools to address in the wild,” says Kevin Zippel, a zoologist and Amphibian Ark’s program officer. “For those species, the only option to avoid extinction is to come into captivity.”

One of the primary culprits killing off amphibians is a fungus. Scientists know that chytrid fungus invades the outer layer of skin, but they don’t yet understand how it kills the creatures, though it might cause them to suffocate. Infected amphibians in captivity can be treated with fungicides, but currently there’s no way to stop the diseases from spreading in the wild.

“We’ve seen amphibian populations decimated by chytrid fungus,” says Karen Lips, a researcher at Southern Illinois University who helped identify the fungus a decade ago. “It’ll move into an area with thriving frog populations and kill about 80 percent of all frogs and about half of all frog species.”

Other factors contributing to amphibian decline include pesticides, habitat loss, and climate change.

The die-offs could have enormous ecological ramifications, potentially disrupting entire ecosystems. Amphibians keep insect populations in check, and serve as a source of food for snakes, birds, and mammals.

Though amphibians might not be as charismatic as the animals that receive most conservation dollars (like pandas and elephants), frogs do have some factors working in their favor: The small creatures are easier to maintain than large mammals, and saving one species from extinction costs as little as $100,000, according to Amphibian Ark.

“You really don’t get better conservation value for the dollar,” says Zippel. “If you took the money it takes to maintain a single elephant for a year, you could save an entire amphibian species from extinction.”  

To help raise the $50 million required to meet its goals, Amphibian Ark has declared 2008 "The Year of the Frog" to rally international support.


Thanks for the very educational story. Good to see that in the Bronx Zoo we have a prototype for what needs to happen everywhere ... for some many other hundreds of species.