An Effective Method of Long-term Control of American Bullfrogs Syntopic With Special-status Native Amphibians in California, USA

American bullfrogs (Lithobates catesbeianus) are invasive in western North America and are well established in California, USA, where they are widespread. This invasive species has been implicated in the decrease of native amphibian populations and is believed to have contributed to the decline of threatened and endangered amphibians regionally. We utilized air rifles, tin alloy pellets, and 2 shooters to systematically control L. catesbeianus in both lentic and lotic habitat types within 2 counties in California. We visited sites monthly (April through November) for approximately 8 and 14 years to lethally target and remove L. catesbeianus from aquatic habitat. The use of air rifles facilitated selective targeting; adult L. catesbeianus were initially targeted to break the reproductive cycle, with subadult L. catesbeianus secondarily targeted and removed when possible. Egg masses, when encountered, were also removed. Habitat type (lentic vs. lotic) did not appear to affect the results of the technique used. We considered L. catesbeianus under control when observed breeding adults were reduced by approximately 95% from original estimates, which occurred within 36 months for both sites. California red-legged frogs (Rana draytonii) were observed recolonizing the lotic site 12 months before L. catesbeianus numbers reached control levels. At the lentic site, foothill yellow-legged frogs (R. boylii) colonized and reproduced in a pond 31 months following the onset of L. catesbeianus control. This technique appears to be highly efficient for L. catesbeianus control, which, if conducted effectively, may support colonization or recolonization of habitat by native anurans.