America's 10 Most Threatened Frogs and Toads
April 28 is Save the Frogs Day! Learn which native amphibians need our help to survive
- Save the Frogs
- Apr 29, 2010
In honor of Save the Frogs Day, April 28, here are ten of the most imperiled frogs in the United States:
1. Sierra Nevada Yellow-Legged Frog (Rana sierrae)
The Sierra Nevada yellow-legged frog was one of the most abundant frog species in California in the early 20th century but has since disappeared from over 90% of the lakes it once inhabited. This is in large part due to a deadly chytrid fungus (Batrachochytrium dendrobatidis) that has spread through the Sierra Nevada mountains in the last decade and decimated the frog's populations. The chytrid fungus has driven up to 100 amphibian species worldwide to complete extinction in recent decades. Pesticides from California's Central Valley also contribute to the species' decline. The windborne chemicals accumulate in the high mountains and are eventually pulled by gravity into the streams and lakes where the frogs live and breed. To make matters worse, non-native trout have been introduced into the naturally fishless mountain lakes the frog inhabits. These invasive trout are voracious predators of tadpoles and can eat frog populations to extinction. Fortunately, frog populations can recover when trout are removed from the lakes. Sierra Nevada yellow-legged-frogs are yellowish or reddish brown from above, with black or brown spots or lichen-like markings. They are highly aquatic and are always found within a meter or two from the edge of water.
2. Dusky Gopher Frog (Rana sevosa)
The dusky gopher frog is a large gray frog from the southeastern United States. While the gopher frog formerly ranged across much of eastern Louisiana, southern Mississippi and southwest Alabama, the the species has disappeared from almost all of its range and now occurs only at one or two breeding ponds in southern Mississippi. The name "gopher frog" refers to the dependence of these frogs on burrows created by gopher tortoises, in which gopher frogs spend most of their lives. But problematically, the tortoises themselves are an endangered species and their burrows are increasingly difficult for gopher frogs to find. During heavy rains, gopher frogs emerge from the tortoise burrows and move to ponds to breed. These frogs are quite selective about the ponds in which they breed: They require ponds that dry out during the winter and are therefore free from fish that would eat their eggs and tadpoles. Unfortunately, temporary ponds preferred by gopher frogs are often drained by humans or altered to hold water throughout the year and stocked with fish.
3. Arroyo Toad (Bufo californicus)
Ranging in color from greenish gray to olive or tan, the arroyo toad is a stout little amphibian with a flattened face akin to that of a pug. Highly specialized in its habitat needs, the toad depends on wide sandy river channels for breeding and is only found in southern California and Mexico's Baja California. In order to successfully reproduce, the arroyo toad requires rivers with a low flow during the spring breeding season. Throughout most of the year the toads lie low, living underground in rodent burrows and crevices, avoiding the hot and dry temperatures brought on by the California summer. In the spring, after winter rains have subsided and stream flows have calmed, male and female toads unite to breed. Under the cover of the moon and stars, male toads call out to their female companions with a high-pitched, rapid trill that sounds like an electronic motor. When the male and female toads meet, eggs are fertilized and tadpoles soon emerge. The tadpoles feed on algae and metamorphose quickly before their aquatic nurseries evaporate in the summer heat. Unfortunately, the arroyo toad is threatened with extinction due to invasive plants and animals, habitat loss, pollution, and climate change, which is drying up its stream habitats.
4. California Red-Legged Frog (Rana draytonii)
California red-legged frogs are the largest native frogs in the western United States. Despite their robust size, the frogs have disappeared from over 70% of their former range. Reasons for decline include habitat destruction and degradation; invasive predators such as bullfrogs, crayfish and mosquitofish; contamination of freshwater habitats; and disease. These handsome frogs are distinguished by reddish-brown to salmon pink coloration, jaunty dark tiger striping on their legs and a pungent, garlicky odor when they are handled. Large females are capable of catching and consuming prey as large as mice and small frogs, though their primary food source is invertebrates. In December-April, timing dependent on the breeding location, males emit a low, burbling, chuckling call in ponds and slow streams to attract females for mating. The result is a grapefruit-sized egg mass attached to emergent vegetation that contains about 2,000 eggs. These eggs hatch into tadpoles that will spend the summer eating plant matter and detritus until they are large enough to metamorphose, generally in the late summer. Ways to help conserve these frogs and other natives include protecting local wetlands, allowing wetlands to follow natural inundation and drying schedules and spreading the word that non-natives should not be released into the wild.
5. Oregon Spotted Frog (Rana pretiosa)
The Oregon spotted frog is a highly aquatic species adapted to living in warm water, a life history unique among Pacific Northwest amphibians. This lifestyle makes Oregon spotted frogs particularly vulnerable to threats from invasive, predatory warm water species introduced to the region. The latter include the American bullfrog (Lithobates catesbeianus) and various spiny-rayed pan fishes (basses, sunfishes). An aquatic lifestyle and a habit of laying eggs in shallow water also make Oregon spotted frogs vulnerable to changes in aquatic habitat. Human-altered aquatic habitat also often favors warm-water predators, so distinguishing the effects of habitat change from those of these predators is often difficult. Invasive exotic plants such as reed canarygrass (Phalaris arundinacea) and yellow flag (Iris decorum) are also thought to impact Oregon spotted frogs in ways that remain poorly understood. Both these plants regularly grow in dense thickets that make unsuitable egg-laying habitat and may impede frog movements. Historically occurring from southwestern British Columbia to northeastern California, the frogs are thought to be extirpated from California, the Willamette Valley of Oregon, and most of the Puget Trough. The frogs are not listed under the U.S. Endangered Species Act, though they are a candidate species. Today, only 40-odd populations remain across their historic range, a number far fewer than the already federally protected California red-legged frog.
6. Foothill Yellow-Legged Frog (Rana boylii)
The foothill yellow-legged frog is endemic to California and Oregon's rivers, many of which have been altered by hydroelectric projects and irrigation systems. The frogs lay their eggs in wide sunlit channels with abundant algae for grazing tadpoles to metamorphose. Genetic research shows that this strategy has been successful for 8 million years, yet it has only taken the last 150 for humans to permanently and drastically transform the riverscapes of the Sierra and Pacific Coast Ranges. Human appropriation of rivers to provide drinking water, deliver irrigation and produce electricity affects stream flow volumes and temperature and has resulted in the disappearance of the frogs from over 50% of their historic localities. The frogs are now rare in rivers with reservoirs and hydroelectric projects and in areas near large dams. Poorly timed flow releases from dams kill eggs and tadpoles, and many non-native predators flourish under the altered flow conditions. Foothill yellow-legged frogs require intact habitat not just at the large rivers, but throughout the watershed, and often move several kilometers, from large rivers to small creeks. The species' current listing as a California Species of Special Concern does not provide the frog with adequate legal protection. For foothill yellow-legged frogs to persist, the species should be listed as threatened.
7. Amargosa Toad (Bufo nelsoni)
The Amargosa toad occurs in Oasis Valley in and around the town of Beatty in Western Nevada. In this extremely arid environment, where rainfall averages four to six inches per year, the toad's survival depends heavily on pools and streams fed by springs. As you might guess, these springs are a valuable commodity for humans as well. So it's no surprise that most of the springs in the valley are privately owned. This could have presented a significant problem for conservation efforts, but for the past 15 years landowners in Oasis Valley have been more than willing to work with the agencies responsible for managing the toad. This partnership has worked to preserve, maintain and create habitat for the toad while also promoting the long-term economic health of the community. The Beatty Habitat and Trails Committee is currently working on a plan to create a trail through town along the Amargosa River, with the Amargosa toad being one of the star attractions. It is hoped that the trail will attract travelers and local residents alike and provide an avenue to teach them about the toad and its habitat.
8. Chiricahua Leopard Frog (Rana chiricauhensis)
Chiricahua leopard frogs (Rana chiricauhensis) live in the middle elevations of mountains in the southwestern United States and northern Mexico. In the 1990's, field biologists reported large numbers of dead and dying frogs from eight different locations in eastern, central, and southern Arizona. The deaths were determined to have been caused by a chytrid fungus. Humans ship nearly 100 million amphibians intercontinentally each year, for the food, pet, bait and laboratory trades, all with virtually no disease testing or quarantine. Sick frogs inevitably escape into the wild and infect native populations. Genetic evidence suggests that the Chiricahua leopard frog species also includes the Ramsey Canyon frog, a group of frogs from southern Arizona that are known for their ability to call under water. Another genetically distinct group of Chiricahua frog populations in central Arizona have almost completely disappeared from their native range and are now being bred in captivity by the Phoenix Zoo and the Arizona Game and Fish Department.
9. Tarahumara Frog (Rana tarahumarae)
Tarahumara frogs are canyon dwellers whose historic range extends from the southwestern United States down to central Mexico. Tarahumara frog die-offs were first noted in 1974, and in the early 1980's the frogs became extinct in the United States. The cause of Tarahumara frog declines is unclear, but the chytrid fungus (Batrachochytrium dendrobatidis) has been found on dead and dying Tarahumara frogs in the field. Introduced species such as bullfrogs and crayfish have also been implicated in the declines of Chiricahua frogs (above). All seven native ranid frog species in Arizona have experienced significant population declines in recent decades. Efforts are currently underway to reintroduce Tarahumara frogs to parts of their former range in southern Arizona.
10. Florida Bog Frog (Rana okaloosae)
Very little is known about the ecology of the Florida bog frog, which was first discovered and described as a new species in the early 1980's. These rare and poorly understood frogs live in a small area of the Florida panhandle, where only a couple dozen populations are known to exist. Bog frogs live and breed in shallow seeps and surrounding streams. The frogs are threatened by residential developments in parts of their range, largely because humans often alter the bogs and streams inhabited by bog frogs. Fortunately, most known populations are located within Eglin Air Force Base, where development is not a threat.
This article was a collaborative project of SAVE THE FROGS, The National Wildlife Federation, and a network of amphibian biologists across the United States, including Steven Whitfield, Nina D’Amore, Frank Santana, Amy Yahnke, Marc Hayes,Brian Hobbs, Sarah Kupferberg, Ryan Peek, Greg Ruthig and Kerry Kriger.
