At a Glance
- The introduction of American bullfrogs to Yosemite in the 1950s has significantly harmed native species, particularly juvenile northwestern pond turtles, by preying on them and limiting population growth.
- A seven-year study found that in areas without bullfrogs, turtle populations thrived, and juvenile turtles reappeared only after bullfrog removal efforts began in 2019.
- Bullfrogs consume a wide range of native wildlife, including small turtles, birds, and newts. This leads to a noticeable increase in turtle size and weight in bullfrog-inhabited areas due to the survival of only larger individuals.
- Although widespread removal may be impractical, targeted bullfrog eradication effectively restores native species and is valuable in conservation-priority habitats.
- The study confirms that controlling invasive bullfrogs can successfully restore ecological balance and promote the recovery of endangered native species in affected environments.
In Yosemite National Park, an invasive species has been disrupting the delicate balance of its ecosystems for decades: the American bullfrog (Lithobates catesbeianus). Introduced to the region in the 1950s, these large frogs became a significant predator to native species, particularly the northwestern pond turtle. New research from the University of California, Davis, has shown that removing these bullfrogs is essential for recovering the native turtle population, providing hope for their conservation. The findings were published in the journal Biological Conservation.
For seven years, researchers conducted an in-depth study to observe how the presence of bullfrogs impacted the local turtle populations. They found that bullfrogs prey on juvenile turtles, which severely hampers the turtle population’s growth in the areas where bullfrogs were present; only older, larger turtles survived, as they were too large for the bullfrogs to consume. On the other hand, in bullfrog-free zones, turtle populations were significantly higher, and juvenile turtles began to return only after bullfrog numbers were nearly eradicated in 2019.
The study showed that bullfrogs impacted turtles and other species in the area. Bullfrogs, known for their ability to eat anything that fits in their mouths, were found to have consumed small turtles, birds, and even newts. Researchers observed that the turtles in bullfrog-inhabited areas were 26% to 36% larger and 76% to 97% heavier than those in areas without the invasive frogs, highlighting the stress and lack of growth in turtle populations where bullfrogs were present.
The researchers concluded that while removing bullfrogs may not be practical for every habitat, it is a promising strategy for regions where the conservation of native species is a priority. The turtles’ return, along with the revival of other native species like frogs and salamanders, underscores the ecological value of controlling invasive species. This study shows that removing bullfrogs can restore balance in ecosystems and provide hope for the recovery of at-risk native species like the northwestern pond turtle (Actinemys marmorata).
References
- Woodruff, S. M., Grasso, R. L., Halstead, B. J., & Todd, B. D. (2025). Effects of invasive American bullfrogs and their removal on Northwestern pond turtles. Biological Conservation, 305, 111090. https://doi.org/10.1016/j.biocon.2025.111090
- Kerlin, K. & U. C. Davis. (2025, May 20). Native turtles return to Yosemite after removal of invasive bullfrogs. Phys.Org; U. C. Davis. https://phys.org/news/2025-05-native-turtles-yosemite-invasive-bullfrogs.html
