A is for Amphibian

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On April 26th, 2021,  Department of Interior Secretary Deb Haaland declared May 2 - 8, 2021 as Amphibian Week in recognition of the vital importance of amphibians (frogs, toads and salamanders) to the nation’s public and private lands.

Did you know that the USGS Ecosystems Mission Area is the biological research arm of the U.S. Department of the Interior?    

USGS Ecosystems Mission Area scientists are leading research and monitoring efforts across the country and in some cases around the globe. Studying topics from amphibians to zoonotic diseases, they provide natural resource managers with the information and data needed to make decisions about the nation’s wildlife and wild places. In the Ecosystems A-Z series, we share just some of the work our scientists are leading from A-Z, starting with amphibians.

Image: Bronze Frog

The bronze frog is common in Louisiana, although amphibian declines are a global problem. (Credit: Dennis Demcheck, U.S. Geological Survey.)

Salamanders, frogs, toads and caecilians (which are limbless and snake-like in appearance) are all amphibians. The United States is home to approximately 300 of the world's estimated 8,000 amphibian species. The number of known species changes periodically as new species are discovered, and new genetic techniques like molecular genetics allow scientists to distinguish among species that are genetically distinct but look the same as other species.

Amphibians are both predator and prey and are considered good indicators of general ecosystem health because of their close association with multiple habitats and sensitivity to different environmental stressors. They can be found in habitats as varied as deserts, prairies, forests and mountains.

Found on all continents except Antarctica, most adult amphibians will eat any live food they can catch and fit in their mouth—insects, small fish and slugs, for example. Life spans in the wild vary among amphibians, normal life spans for most species range for 2 to 10 years or more, but some live substantially longer.

Across the country, USGS scientists are conducting research on amphibians to provide information that helps other agencies manage this historically underappreciated and now declining group. Our scientists have learned that no single threat explains global amphibian declines and instead that a variety of local and global factors are contributing. Habitat loss, disease, contaminants and other threats are all part of the pattern.

Across the Nation

Image of Blake Hossack

USGS scientist Blake Hossack demonstrates swabbing the skin of a boreal toad to detect the amphibian chytrid fungus, to the Conservation Ecology class from the University of Montana. (Credit: USGS)

The USGS ARMI program—Amphibian Research and Monitoring Initiative—is devoted to research on amphibians, because information to support natural resource management decisions related to  amphibians is a major need of our partner agencies. ARMI provides a wide variety of decision support for natural resource managers, but is particularly focused on amphibian disease, as well as science to inform decisions for species that are federally listed as threatened or endangered.

Water is a critical component of ARMI research, and researchers are examining the effects of water availability nationwide to understand how water quality, quantity or timing affect amphibians. This research includes questions about how water quality (e.g., nutrients, chemicals), water budgets (e.g. daily to yearly changes in water availability), storm surge impacts or other hydrologic conditions can affect amphibian life cycles, disease transport or habitat quality.

Another critical effort of ARMI scientists is laboratory research and field surveillance for diseases such Bsal and Bd. Bsal, or Batrachochytrium salamandrivorans, is a pathogen capable of causing significant illness and death in salamanders that to date has not been found in the United States, and Bd, or Batrachochytrium dendrobatidis, is an aquatic fungus that causes Chytridiomycosis, an infectious disease of amphibians. ARMI researchers are estimating the impacts of diseases on the growth of populations to understand how various environmental conditions can be managed to affect disease outcomes.

Close up of a Northern Leopard frog (Lithobates pipiens) in a wetland

Northern Leopard frog (Lithobates pipiens) in a wetland in Worth County, Iowa. Scientists tracked 72 northern leopard frogs in two wetlands in an agricultural setting in Iowa for insights into where and when individual adult frogs are likely exposed to pesticides. (Credit: Clay L. Pierce, USGS Iowa Cooperative Fish and Wildlife Research Unit) 

Even with a national approach to understanding amphibians, there is research that is regionally specific. In the Midwest for example, a pilot project is underway at Indiana Dunes National Park by researchers from the USGS Cooperative Research Unit-Vermont. They are monitoring wildlife species that vocalize, including birds and amphibians, using acoustic sampling. Researchers are using cell phones to collect and transmit acoustic data and imagery automatically and are incorporating cutting-edge technologies and approaches such as machine learning to identify species. This research will help managers take effective actions to restore the wetlands and savannas by providing information on when and where species, especially species that are well camouflaged, are found. This project has the potential to significantly benefit species such as the Northern leopard frog and Fowler’s toad, and provide local community, recreational and educational opportunities.

Image: California Red-legged Frog

California red-legged frog (Rana draytonii) surfaces in a pond in Point Reyes National Seashore, CA. (Credit: Gary M. Fellers, USGS.)

Last year, in a historic and exciting first, the federally-threatened California red-legged frog was successfully reintroduced to southern California where the frogs have been absent for over 20 years. California red-legged frogs were in decline statewide since the 1970s and ultimately disappeared from a 250-mile stretch between southern California and northern Baja California largely due to habitat loss, fungal disease and predation by non-native species. The species was listed under the Endangered Species Act in 1996.

In April 2020, an international group of researchers and conservationists collected eggs from a genetically similar population of red-legged frogs in the Sierra San Pedro Mártir mountain range in Mexico and transported them to Riverside and San Diego counties, California. The eggs were placed into ponds in protective cages, allowing the tadpoles to grow and develop into frogs safely before they are fully released into the wild. To ensure a successful reintroduction, invasive species were removed from the release sites and locations will continue to be closely monitored to protect from any new invaders or other threats.

The binational group of scientists represent agencies and organizations from the United States and Mexico, including the Conservación de Fauna del Noroeste (FAUNO), San Diego Natural History MuseumThe Nature ConservancyU.S. Fish and Wildlife Service and the USGS.

Chiricahua leopard frog with radio tracker

Radio-tracking Chiricahua leopard frogs as part of the amphibian monitoring program coordinated by U.S. Fish and Wildlife Service at Buenos Aires National Wildlife Refuge and the Amphibian Research and Monitoring Initiative (ARMI) of the U.S. Geological Survey. (Credit: Brent H. Sigafus, USGS)

To answer some of the conservation questions in the Southwest, a hands-on approach is currently being implemented for the Chiricahua leopard frog. This species was federally listed as threatened in 2002, primarily in response to habitat loss, threat of invasive predators and disease. A highly aquatic frog spending most of its life in the water, it is native to the southwestern United States and Mexico. Previously found in semi-permanent wetlands and slow-moving sections of canyon streams, the Chiricahua leopard frog populations are now found primarily in isolated ponds constructed for livestock. In southern Arizona, management and recovery efforts are under study with federal, state, university and nonpublic partners on the Buenos Aires National Wildlife Refuge. There, the Chiricahua leopard frog population has been growing since it was reintroduced from tadpoles produced via a captive population that was originally rescued near the refuge. Invasive American bullfrogs, which prey on and compete with the Chiricahua leopard frog, are being removed from most areas within the refuge and from some neighboring areas with remnant leopard frog populations. The greatest threat to leopard frog recovery is likely the American bullfrog and other non-native predators, but growing evidence indicates that leopard frog populations can rebound quickly when predators are managed.

In the Pacific Northwest, ARMI scientists work with state and federal partners to better understand how the Tailed Frog lives in managed forests that are important for timber production.  The two species of tailed frog are the most ancient living frogs in the world and are only found in the northwestern portion of North America.  They have been around since the Cretaceous Era when dinosaurs were still alive and live in and around cold, steep, headwater streams. The tadpoles have large suction-cup like mouths that allow them to cling to rocks in fast currents. These survivors were one of the first vertebrates documented in the blast zone after the eruption of Mt Saint Helens. Current forest practices have improved the habitat conditions for this ancient species compared to historic practices.  

Scientist David Hurtado holds a Sonoran tiger salamander

Scientist David Hurtado holds a Sonoran tiger salamander. (Credit: USGS)


In this episode of the USGS Ecosystems Mission Area Outstanding in the Field podcast series, we describe the USGS’s efforts to track frog populations in the southeast United States. 

USGS researchers are helping unravel the mystery of the federally-endangered Sonoran tiger salamander, native to the United States and Mexico. Found only in one small valley on the Arizona-Sonora border, this salamander is threatened by several factors including the loss of natural wetland habits, frequent die-offs from disease and reproduction with the invasive Barred tiger salamander. Field surveys to look for the Sonoran tiger salamander in Sonora in the 1980s found none, indicating that it was rare or absent. Recent searches, though, show that tiger salamanders are now not only common, but widespread in areas of the Sonora where they were not found in the 1980s.

Whether scientists are marking, radio-tracking, trapping, listening to amphibian calls or evaluating eDNA, USGS researchers are providing the needed answers to critical questions to understand amphibian population declines and to aid in their recovery.