Bullfrog Eradication Brings Native Turtles Back to Life in Yosemite
In a remarkable victory for native wildlife, the eradication of invasive American bullfrogs from parts of Yosemite National Park has led to the return of California’s only native freshwater turtle, the northwestern pond turtle — a species proposed for federal protection under the Endangered Species Act.
The bullfrog, introduced to Yosemite in the 1950s, had become an ecological menace. Described by scientists as one of the world’s worst invasive species, the voracious amphibian eats almost anything it can fit in its mouth — including juvenile turtles, newts, salamanders, and even other frogs.
“It was like looking out over a galaxy of glowing eyes,” said UC Davis Ph.D. candidate Sidney Woodruff, recalling her early fieldwork in frog-infested ponds. “Their croaking drowned out everything else. It felt normal — but it wasn’t.”
Between 2016 and 2022, Woodruff led a multi-year study across four sites within the park to document the ecological impact of bullfrogs and test whether their removal could revive native species populations. Her findings, recently published, reveal a clear and powerful conclusion: bullfrogs had to go before turtles could come back.
Working with senior author and wildlife professor Brian Todd, the team conducted labor-intensive removal operations — collecting egg masses by hand during the day and capturing adult frogs at night, followed by humane euthanasia. In ponds cleared of bullfrogs, turtle populations surged, showing 2 to 100 times more individuals than in ponds still dominated by the invasive species.
The study also noted a telling absence of juvenile turtles in bullfrog-infested areas. “It took over two years to spot a single juvenile turtle in a pond with bullfrogs — and that was after eradication,” said Woodruff. This gap in the age distribution strongly suggests that bullfrogs had been preying heavily on turtle hatchlings, making it nearly impossible for the population to sustain itself.
As bullfrog numbers dropped, so did the silence. Native frogs and salamanders returned, their songs once again echoing through the Yosemite wetlands. “To hear those natural choruses again was incredible,” said Woodruff. “It shows the ecosystem can recover if we give it a chance.”
Outside of California, the American bullfrog has wreaked havoc globally, with invasive populations in South America, Europe, and Asia. But in Yosemite, this success story shows that well-targeted intervention can turn the tide.
“All across California, the only freshwater turtle that should be there is the northwestern pond turtle,” said Todd. “Without it, we lose part of our natural heritage.”
The findings offer a hopeful template for other ecosystems battling invasive species. Yosemite’s rejuvenated wetlands are now not only a haven for turtles — but a reminder of what’s possible when science, persistence, and ecological stewardship come together.