Genetic Analysis Supports Frog Reintroduction Effort in Santa Monica Mountains

Once widespread, California red-legged frogs (Rana draytonii) are now rarely found in southern California riparian habitats. Streams in this densely-populated, highly-developed area are extremely sensitive to change. When even just 15% of a watershed becomes developed, a once ecologically intact stream can rapidly shift into one dominated by non-native flora and fauna.

Once thought to be extirpated (completely removed) from the Santa Monica Mountains, a single population of California red-legged frogs was discovered in protected habitat nearby. Years of careful monitoring led biologists to believe that the population was healthy enough to supply other nearby streams with adults and eggs.

NPS / Michael Ready

National Park Service (NPS) biologists and managers work tirelessly to protect the habitat and species under their care and oftentimes the simple act of protecting habitats from external threats is enough to maintain healthy wildlife populations. But occasionally, the NPS must intervene and restore native wildlife back into the places they used to call home. Once thought to be extirpated (completely removed) from the Santa Monica Mountains, a single population of California red-legged frogs was discovered in protected habitat nearby. Years of careful monitoring led biologists to believe that the population was healthy enough to supply other nearby streams with adults and eggs, which would form the building blocks of new frog populations.

However, while it may sound easy to move frogs and their eggs around from one stream to another, it’s never quite that simple. In order to ensure long-term success, biologists need to maximize genetic diversity across the frog’s populations. Thus, understanding the genetic structure of the California red-legged frog population is a critical prerequisite of any relocation plan. When the National Park Service first began to translocate red-legged frogs, the US Geological Survey supported the effort in various ways, including genetic analyses of the existing populations.

While that data was invaluable at the time, any future translocations would require additional evidence to justify movement of frogs to new locations within the mountains. The Southern California Research Learning Center has since stepped in to support fresh genetic analyses of numerous frogs in the Santa Monica Mountains. This information can help NPS biologists decide which areas may provide the best source of new genetics and where they can safely move frogs to best maintain genetic diversity.

Prior to the Woolsey Fire in 2018, California red-legged frogs had been transplanted to four streams in the Santa Monica Mountains and were found to be breeding on their own in at least one of the translocation sites. Even now, despite the cataclysmic nature of the Woolsey Fire, the species is still found in at least one of the translocation sites. That is a testament to both the strength of the NPS translocation plan and the tenacity of the frogs!

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A Publication of the Southern California Research Learning Center

The Southern California Research Learning Center is one of 18 Research Learning Centers across the country. These centers strive to increase scientific activity in the national park system, to communicate research that supports stewardship and to make science part of the visitor experience. By working with a variety of partners, we aim to support science-based decision-making, increase science literacy and promote a conservation ethic within the Santa Monica Mountains National Recreation Area, Channel Islands National Park, and Cabrillo National Monument.