Amphibian Research in Southern California

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Amphibian populations have declined in many areas around the world. Initially, there was skepticism as to whether the observed declines were merely minor population fluctuations, but it has become increasingly clear that many declines are both real and sustained. At the request of the U.S. Department of the Interior, USGS Western Ecological Research Center (WERC) scientists are supporting the development of a national monitoring program for amphibians to detect stressors in the environment.

Approximately 230 species of frogs, toads, and salamanders make up the amphibian fauna of the continental United States. Their sensitivity to environmental conditions make them ideal sentinels of environmental stress.

Data collected in California clearly documented not just a decline in frog and toad populations, but the collapse of certain species throughout significant portions or their range. The causes of the amphibian losses are largely unknown, but several human and natural factors are suspected, including air pollution, acid precipitation, increases in ultraviolet light, the introduction of native and non-native predatory fish into previously fishless stream and lakes, long-term fire suppression, extended drought, severe freezes, and disease.


Amphibian Research Monitoring Inventory Database (ARMI)

The U.S. Department of the Interior has called for the development of a national program for monitoring amphibians and understanding their declines. This need stems from the overwhelming evidence that this class of vertebrates may be declining faster than other classes and that these declines may be due to environmental degradation, even within apparently pristine wilderness.

Department of the Interior agencies (National Park Service, Bureau of Land Management, Bureau of Indian Affairs, and Fish and Wildlife Service) currently manage very diverse lands and habitats across the nation. These areas are an ideal network to begin developing a national monitoring program for amphibians where these species can serve as an “early warning system” for environmental stress.

The U.S. Southwest has been hit hard by amphibian declines, leaving a high proportion of species as sensitive or endangered. Under the guidance of Dr. Robert Fisher, WERC scientists are looking intensively at California and Arizona in an attempt to begin tracking populations, understand the magnitude of these declines, and identify causes. This area includes a variety of habitats, including high elevation and some low elevation creeks and lakes, vernal pools, and deserts with temporary pools. Data collected on populations living in this region are contributing to the national ARMI database and informing the management of sensitive amphibians.


Mountain Yellow-Legged Frog

Photo of an endangered mountain yellow-legged frog

Mountain yellow-legged frog. (Credit: Adam Backlin, USGS Western Ecological Research Center. Public domain.)

With Fisher’s guidance, Adam Backlin and Elizabeth Gallegos collaborate with the Association of Zoos and Aquariums and other partners to stabilize existing populations and establish new wild populations of the endangered mountain yellow-legged frog (Rana muscosa) in southern California. Their efforts are informing programs that raise and translocate healthy, captive populations of mountain yellow-legged frogs to areas where they thrived in the past. The team also:

  • Radio tracks wild frogs to collect data on their activity and hibernating habitats, to help local zoos inform their husbandry and breeding programs.
  • Uses water temperature loggers to determine if changes in water temperatures are causing population changes and/or disturbances.
  • Monitors the spread of the devastating fungal disease chytridiomycosis (or simply “chytrid fungus”) in mountain yellow-legged frogs

The team will ultimately provide these data as support in the U.S. Fish and Wildlife Service’s development of a Recovery Plan for the mountain yellow-legged frog.


California Red-Legged Frog

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. Public domain.)

The once-common California red-legged frog (Rana draytonii) has vanished from most of its historical range in southern California. In 1996, the species was listed as “threatened” under the Endangered Species Act.

Because there are so few populations, recovery of the species depends on stabilizing existing populations and reestablishing additional populations to watersheds with suitable habitat. The U.S. Fish and Wildlife Service’s recovery plan identifies the reestablishment of historic populations as a criterion to consider for delisting. The plan also calls for the augmentation of existing populations and the reestablishment of extirpated populations as priority recovery actions in southern California.

The USGS is currently using genetic techniques to characterize existing California red-legged frog populations in the southern part of their range. These methods will enable the USGS to determine:

  1. Whether any of the populations are genetically unique
  2. The recent population history of these populations
  3. The level of genetic diversity within populations.
  4. Effective population sizes

The Fisher team is also leading egg mass surveys within southern California’s Angeles National Forest and the Santa Monica Mountains, and translocating California red-legged frogs. Altogether, these efforts and data will inform future conservation of the species.


Arroyo Toad

Arroyo toad

This little singing male is an arroyo toad, an endangered species found in California. (Public domain.)

The endangered arroyo toad (Anaxyrus californicus) lives only in the coastal plains and mountains of central and southern California and northwestern Baja California. Currently, this species only occupies an estimated 25% of its previous habitat within the United States.

The Fisher team leads several projects aimed at long-term monitoring of existing populations of arroyo toads across southern California, studying arroyo toad ecology, arroyo toad response to disturbances such as fire and to changes in hydrology from dam operations, and arroyo toad seasonal movements and use of flood plain and upland habitats.


Western Spadefoot

Fisher and colleagues conducted surveys in 2016 re-evaluating a spadefoot (Spea hammondii) habitat creation and translocation site constructed in 2005. The translocation was successful with all age classes of spadefoot at the site. 


Collage of reptiles and amphibians affected by roads

Credit, counter-clockwise from top: Amphibian tunnel/Tom Langton, Western pond turtle/Chris Brown, Racer/Gary Nafis, CA tiger salamander/Jerry Dodrill. (Public domain.)

Road Ecology Research

At the request of the California Department of Transportation (Caltrans), Fisher and biologist Cheryl Brehme are collaborating with the Western Transportation Institute out of Montana State University to create best management practices for barrier and crossing systems supporting amphibians and reptiles in California. To inform this effort, USGS has developed a risk assessment method to identify species likely at greatest risk from roads within their habitat. The team is conducting field research to answer questions regarding the effectiveness of road mitigation systems for reptiles and amphibians. This includes studies of barrier materials, fence-end ‘turn-arounds,’ design of escape ramps, use of existing underpasses, and enhancements to underpasses to better simulate moisture, light, and cover conditions in the surrounding environment.