Defenders Magazine

Slipping Away

Frogs, salamanders and other amphibians are sliding into oblivion

by Sara Shipley Hiles

© Brad Wilson/Atlanta Botanical Garden (captive)

In the wetlands of northwest Iowa, where hunters once collected 20 million frogs a year for their meaty legs, there is only one leopard frog left for every thousand frogs the pioneers saw.

In southern Missouri's mountain streams, scientists struggle to protect dwindling populations of the Ozark hellbender, a wrinkled, primitive salamander that can grow to two feet long.

All around the planet, amphibians such as these are in trouble. It's not just the colorful, exotic rainforest species that are disappearing, but also the common frogs, toads, newts and salamanders that people used to see in backyards across America. A third of all amphibian species are considered threatened, making them the most vulnerable group of animals in the world. By comparison, 12 percent of birds and 23 percent of mammals are threatened.

Amphibians—named for the Greek word for "double life"—are moist-skinned vertebrates that have distinct larval and adult stages. Typically spending part of their lives on land and part in water, these change artists have thrived on Earth for 360 million years. But without swift action, many scientists and conservationists believe that much of their diversity will soon vanish. An estimated 120 of approximately 6,000 known amphibian species have disappeared in the past 25 years, and another 2,000 to 3,000 species may go extinct in our lifetimes.

"It sounds like hyperbole, but really, this is the greatest conservation challenge humanity has ever faced," says Kevin Zippel, program officer for Amphibian Ark, a $50-million effort to collect critically endangered species from the wild for protection and breeding in zoos and aquariums. "The world hasn't seen an extinction crisis like this since the dinosaurs died out."

The Amphibian Ark is part of a larger program, the Amphibian Conservation Action Plan, created by staff from conservation groups, universities, zoos, government agencies and others around the world. This is a broad plan to counter threats to amphibians, which range from habitat loss, disease and overharvesting to global warming, pollution and UV radiation. The estimated cost of this effort is $400 million over a five-year period.

To help raise awareness and funding for amphibians, organizers have dubbed 2008 the "Year of the Frog." The campaign kicked off on New Year's Eve with a series of "leap year" events focused on the plight of amphibians. Other activities planned for the year include a worldwide petition drive and special events at zoos, aquariums and museums. The tone of these celebrations is light, but the crisis behind it often has herpetologists speaking in somber tones.

"These are tragic circumstances we find ourselves in," says George Rabb, retired president of the Brookfield Zoo in Chicago and a member of Defenders of Wildlife's board. "We either do something to give amphibians some security, or it's likely that many of these creatures will absolutely vanish from this Earth."

The most urgent problem, scientists say, is a fungus that can kill up to 80 percent of native amphibians within months of its arrival in an area. Formally known as Batrachochytrium dendrobatidis, or Bd for short, the deadly agent is commonly referred to as a chytrid fungus.

Biologist Karen Lips helped track the fungus' wavelike spread through Central America. In 1992, she encountered a handful of dead frogs in Costa Rica, but she didn't think much of it. Four years later, when she found 50 dead frogs at a site in Panama, she knew something was wrong. The frogs looked fine, but they didn't move, as if they had been frozen in place. "It's like they went to sleep sitting on their little rock or leaf, and they just died right there," says Lips, who works at Southern Illinois University in Carbondale.

The frogs died of a chytrid infection, but no one knew that at the time. The fungal disease wasn't identified until 1997, when scientists from around the world gathered to look at the organism under an electron microscope and agreed that it was the same pathogen decimating frogs from Australia to the United Kingdom. Since then, the fungus has been discovered in most of the world, with a few exceptions, such as Madagascar, New Guinea and parts of Asia, Rabb says.

The origin of the fungus is still a mystery. The prevailing hypothesis holds that it originated in Africa and spread around the globe through the export of the African clawed frog, a common lab animal once used in human pregnancy testing. More recently, trade in the American bullfrog and other species used for food and pets may have spread the fungus, but no one is quite sure how it gets around. It is unstoppable and untreatable in the wild. "We can't really track it in nature yet," Lips says. "We just stake it out and wait for it to get there."

Some amphibians appear to be immune to the disease, but others are completely wiped out. Joe Mendelson, curator of herpetology at Zoo Atlanta, compares the spread of chytrid to the smallpox epidemic that swept through Native American populations after European settlers arrived, leaving few survivors. "That's what we have with amphibians right now—groups that have survived," he says. "In southern Mexico, at one of my study sites, there are still amphibians there, but you're looking at what was left after everything else was killed."

After witnessing six or seven population crashes and finding hundreds of dead frogs in Central America, Lips is shifting some of her work to the United States. She plans to embark on a survey of frogs across Illinois to see how widespread the pathogen is there. "Honestly, we're limited in what we can do down there (in Central America), because we're running out of frogs," she says.

Such sobering realizations have led to amphibian rescue missions like one Mendelson helped lead at a site known as El Valle in Panama in 2005. With the blessing of the Panamanian government, a team of Americans and Panamanians conducted what Mendelson calls a "pre-emptive conservation strike," capturing about 600 frogs from 35 species and taking them back to facilities in Atlanta. At the same time, the Houston Zoo was building an amphibian conservation center in Panama. Within a year of the extraction, the fungus showed up at El Valle and wreaked its havoc, and "now the place is almost completely frogless," Mendelson says.

The Amphibian Ark program promotes more of these rescue operations for about 500 species deemed to be in imminent danger. Zippel says the Ark will target many species in tropical forests, where the fungus is hitting particularly hard, but it will also include American species such as the California mountain yellow-legged frog and the Mississippi gopher frog. Each species will be housed in two biologically secure facilities to guard against unexpected loss. For remote areas, commercial shipping containers can be converted into self-contained labs run on solar power. "Literally, wherever amphibians are in need, we can put one" of the labs, Zippel says.

The idea is to keep a sliver of the population alive so that the animals can be released to the wild when—or if—it's safe. "We could have the fungus cured tomorrow, or never," Zippel says. "It's really a stopgap measure, to buy us some time."

Even if chytrid fungus could be tamed, amphibians face a host of other problems. Habitat loss is still chief among them, according to a 2004 global survey. Mike Lannoo, editor of a comprehensive book about amphibian declines in the United States, blames habitat loss for the one amphibian extinction documented in the United States to date. "The Vegas Valley leopard frog was last seen in 1942. Basically, Bugsy Siegel built Las Vegas over its habitat," Lannoo says.

Of the 291 species remaining in the United States, Lannoo estimates that two-thirds are in decline. About 10 percent are at severe risk. Only a few are increasing in numbers, often because of their introduction into non-native habitats, he said. Even those species that are still common are less so than they once were, he says.

For example, leopard frogs swarmed the shores of Lake Okoboji in northwestern Iowa so heavily a century ago that hunters were able to collect 20 million of the spotted greenish-brown frogs a year. "If you go to that same spot now, which I have, what you find is a three orders of magnitude decrease. You might say there are still plenty of frogs, and that's true, but there are 1,000 times fewer frogs," Lannoo says. Swamp draining in the early 20th century killed the commercial frog industry, and later, amphibians suffered from the application of pesticides and the introduction of carnivorous sport fish such as muskies, he says.

The tiger salamander, the most widespread salamander species in the United States, is another example of a once-common species that has declined. Growing up to a foot long, the tiger salamander is secretive, spending most of its time burrowed underground. While still thriving in some areas, tiger salamanders have been eliminated in much of their former range, and a number of studies have documented sharp drops in local populations.

"The biggest factor in amphibian decline is habitat loss and habitat alteration," Lannoo says. "But as a society, the things we're doing almost universally negatively impact amphibians: global warming, ozone depletion, acid rain, applying pesticides, planting non-native species, moving fish around, spreading disease."

Adding these factors together may create the perfect storm that's killing amphibians. Threats to the Ozark hellbender salamander, for example, include habitat loss, overcollection and pollution from man-made chemicals, such as endocrine disruptors. Recently, researchers found some hellbenders infected with chytrid fungus as well.

Tyrone Hayes, the University of California-Berkeley researcher who has studied the impacts of the weed-killing chemical atrazine on frogs, says that environmental chemicals play a significant role in amphibian decline. Hayes led a recently published study that found immune system damage in frogs exposed to a cocktail of nine pesticides commonly used on corn fields. "I would never say atrazine and other pesticides are causing the global amphibian decline, but I do think they're involved by making them more susceptible to diseases that would otherwise not impact them," he says. (Syngenta, a major manufacturer of atrazine, says its studies have not found the herbicide to be harmful to amphibians. "We saw no effect on sexual development, and no effect on the general health of the animal either," says Tim Pastoor, principal science advisor for Syngenta. Although atrazine is banned in some European countries, the U.S. Environmental Protection Agency re-approved its use in 2006.)

If amphibians disappear, what then? Lips' work has shown a cascade of effects in the ecosystem. Amphibians sit in the middle of the food web, so when frogs go, it affects both the things they eat and the things that eat them. Tadpoles eat algae and sediment in streams, so if there are no tadpoles, algae grow unchecked and sediment increases, leading to changes in water quality and aquatic insects. Adult frogs eat insects, so if there are no hungry frogs, some insect populations boom. And some snakes depend on frogs for food, so without their prey, those snakes may starve to death.

Amphibians also carry secrets of biomedicine that could be lost forever. Researchers at Vanderbilt University in Nashville have discovered anti-microbial substances in the skin of certain frogs that stopped HIV infection. The Australian red-eyed tree frog had the highest levels of such virus-blocking substances. "Theoretically, there could be some kind of cream developed that could protect against HIV transmission," says Louise Rollins-Smith, a microbiologist who participated in the study.

The other selfish reason for humans to take notice is that frogs and salamanders are telling us something, says Robin Moore, an amphibian specialist at Conservation International who is helping to coordinate the worldwide amphibian conservation plan. "Amphibians are sensitive to change, and may simply be the first to go. They are sounding an alarm, an early warning that the ecosystems in which they live are not healthy," he says. "We do not know what will be next to go—birds, mammals—or us?"

Learn more about the conservation of amphibians.

Sara Shipley Hiles is a freelance writer specializing in environmental topics. She teaches journalism at Western Kentucky University.