Vanishing Frogs
Welcome to the Vanishing Frogs website Seven species no longer with us Why frogs are vanishing How you can help save frogs Hope for a vanishing frog Test your knowledge of frogs and their plight Frog websites

Why frogs are vanishing

Before we look into the reasons why, should we even care that frogs are vanishing?

o If we humans are responsible, we have a moral obligation to prevent amphibian disappearances.

o Frogs may directly benefit humans. Australia’s gastric-brooding frog, now extinct, had an enzyme-suppression mechanism that might have helped people with gastric ulcers.

o Frogs eat disease-carrying insects.

o Frogs are critical links between predators and the bottom of the food chain (algae, plants, detritus, and such). Frogs feed on many organisms, and many organisms feed on them. Remove the frogs, and important links are knocked out of the food chain.

o Frogs are important indicators of environmental health. Because most frogs spend their early days in water and their adult life on land, changes in both worlds may affect them.

Frog numbers are dropping in at least 140 countries. Biologists have identified a number of reasons but suspect that a combination of factors may be responsible.

Loss of habitat



Introduced aquatic predators

James P. Blair

The number one cause of amphibian decline is habitat loss, and we humans are to blame. By cutting down forests, damming rivers, and draining marshes to build houses and shopping centers, we ravage landscapes around the world.

Evidence: Most amphibians feed and breed in wetlands, so loss of wetlands equals loss of amphibians. In the past half-century the lower 48 states have lost more than half of their estimated original wetlands.

Evidence: Urban development in southern California has gobbled up 75 percent of the range of the endangered arroyo toad (Bufo microscaphus californicus). Now the toad must compete with weekend gold miners, fishermen, campers, and off-road fanatics for use of its few remaining streams.

Evidence: In the United Kingdom, where many breeding ponds have been filled in (as many as 80 percent in some areas), all six native amphibian species have suffered dramatic population declines.

Erik Enderson


Amphibian diseases may be carried from continent to continent by aquarium fish and exotic animals sold as pets. Disease may also spread to frog populations on people’s boots or by birds, insects, and livestock. Before tadpoles are moved from one area to another to reestablish frog populations, biologists give the youngsters a clean bill of health to prevent the spread of disease.

Evidence: A deadly virus is the likely culprit in several recent die-offs of frogs, including spring peepers at Acadia National Park in Maine, wood frog tadpoles in Massachusetts, mink frogs in Minnesota, wood frogs and bullfrogs in North Carolina, and numerous frogs at the Great Smoky Mountains National Park in Tennessee.

Evidence: Several species, such as Costa Rica’s golden toad, may have disappeared because of chytrid (KIH-trid) fungus (see photo). This infectious fungus spreads in water and can wipe out entire populations or species even from pristine habitats. The frogs most affected live in streams in mid- to high-elevation rain forests. Climate change may also play a role.

Evidence: Scientists have detected chytrid fungus on almost a hundred species of amphibians on six continents. More than 40 of those species are in Australia. Chytrid fungi are common in nature, but this is the first one known to have attacked vertebrates.

Evidence: Most studies of amphibian disease are done in a lab or on dead specimens. When Don Nichols, a pathologist at the National Zoological Park in Washington, D.C., put antifungal medication on captive frogs infected with chytrid fungus, the frogs recovered. This method is being used to treat infected frogs in other zoos and private collections.

Eric L. Williams


Amphibians have vanished even from wilderness areas. As Earth’s ozone layer thins, increased ultraviolet radiation may undermine the hatching success of the eggs of certain amphibians. (Most amphibian eggs have a gelatinous coating but no protective shell.) UV radiation can also alter the DNA in frogs’ cells and suppress immune responses. At risk: Frogs that live at cooler, higher elevations and extreme latitudes, where the ozone layer is thinner but where amphibians must bask in the sunlight to regulate body temperature.

Evidence: Increased exposure to ultraviolet radiation may damage the eggs of the Cascade frog (Rana cascadae), which lays its eggs in shallow water in high mountain meadows.

Evidence: Global warming may have caused the erratic weather that ruined the breeding efforts of the golden toad in Costa Rica’s cloud forest. In 1986-87 warm, dry weather dried up the pools before the toads’ larvae had matured. Of a potential 30,000 toads, only 29 survived. The drought may have caused the toads and other amphibians to concentrate at the remaining pools, which facilitated the transmission of disease and resulting death from the chytrid fungus.

Evidence: Eggs and tadpoles need moisture to develop. In southern California the endangered arroyo toad (Bufo microscaphus californicus) lays its eggs in shallow pools created by spring rains. During dry periods the toad can’t reproduce.

Evidence: In times of drought, frogs can become more susceptible to disease or even dry up and die. When drought threatened a colony of Chiricahua leopard frogs (Rana chiricahuensis) in southeastern Arizona, a conservation-minded rancher trucked in a thousand gallons of water a week for two years.

James P. Blair


Since frogs breathe at least partly through their thin, porous skin, they’re very susceptible to toxins. Industrial pollution may be wiping out local populations. In farm areas, herbicides and pesticides run off into the ponds, watering tanks, and irrigation canals where frogs live and breed. Some herbicides interfere with respiration, and certain pesticides and their by-products produce severe limb deformities that prevent frogs from fleeing predators.

Evidence: Pesticides drifting up from farmland may be killing amphibians in California’s Sierra Nevada and other wilderness areas.

Evidence: Acid rain from air pollution can turn lakes, streams, and wetlands into death traps. In Canada, Europe, and the northeastern United States, acid rain has damaged forests and polluted soil and water, making some areas unlivable for frogs.

Cecil Schwalbe



When sport and bait fish, crawfish, and bullfrogs (Rana catesbeiana) invade lakes and wetlands where they’ve never lived, these predators often devour native frogs and their prey. Humans introduce most aquatic predators for sport and food, while others escape from captivity or sneak in as stowaways on potted plants.

Introduced trout have nearly wiped out the mountain yellow-legged frog (Rana muscosa) in California’s Sierra Nevada.

Evidence: In southeastern Arizona sport fish and the bullfrog, introduced from the eastern United States a century ago, have nearly eaten the Chiricahua leopard frog (Rana chiricahuensis) out of its native waters. The aggressive, fast-growing bullfrog devours anything it can fit in its mouth: tarantulas, native frogs, rattlesnakes, bats (see photo), songbirds, and many other creatures. A bullfrog can lay as many as 20,000 eggs per clutch.


People harvest frogs for food as well as for hides, pets, and research. Some states and countries have banned the commercial harvesting of frogs for dissection in biology classes. Frog-friendly alternatives include videotapes, 3-D anatomical models, and interactive CD-ROMs.

Evidence: In the late 1800s the massive collecting of California red-legged frogs (Rana aurora draytonii) for food depleted local populations, which led to the introduction of bullfrogs (Rana catesbeiana).

Evidence: Between 1981 and 1984 Americans devoured more than 6.5 million pounds of frog legs a year, which led to the death of some 26 million frogs annually. Ninety percent came from India and Bangladesh, which banned exports after frog declines led to growing hordes of mosquitoes, malaria, and increased use of pesticides. Now Indonesia supplies most of the frogs for restaurants.