Action: Remove or control invasive bullfrogs
- One replicated, before-and-after study in the USA found that removing American bullfrogs significantly increased a population of California red-legged frogs.
- One before-and-after study in the USA and Mexico found that eradicating bullfrogs from the area increased the range of leopard frogs. One replicated, before-and-after study in the USA found that once bullfrogs had been removed, California red-legged frogs were found out in the open twice as frequently.
The American bullfrog Rana catesbeiana has been introduced to many parts of the world. The species is relatively large and adaptable and has significant effects on some native species through competition for resources and predation.
There is additional literature that is not included here examining the success of controlling bullfrogs, which may be undertaken for the conservation of a range of taxa including amphibians (e.g. Banks et al. 2000; Orchard 2011; Louette 2012). For example, one modelling study found that culling bullfrog metamorphs in autumn was the most effective method of decreasing population growth rate (Govindarajulu et al. 2005). A review suggested that an indirect approach, by managing habitat rather than directly controlling bullfrogs, may be a more effective way to reduce the effects of bullfrogs on native amphibians (Adams & Pearl 2007). For the success of control of American bullfrogs see the Control of Freshwater Invasive Species synopsis.
Adams M.J. & Pearl C.A. (2007) Problems and opportunities managing invasive bullfrogs: is there any hope? 679–693 in: F. Gherardi (eds) Biological invaders in inland waters: profiles, distribution and threats, Springer, Dordrecht, The Netherlands.
Banks B., Foster J., Langton T. & Morgan K. (2000) British bullfrogs? British Wildlife, 11, 327–330.
Govindarajulu P., Altwegg R. & Anholt B.R. (2005) Matrix model investigation of invasive species control: bullfrogs on Vancouver Island. Ecological Applications, 15, 2161–2170.
Louette G. (2012) Use of a native predator for the control of an invasive amphibian. Wildlife Research, 39, 271–278.
Orchard S.A. (2011) Removal of the American bullfrog Rana (Lithobates) catesbeiana from a pond and a lake on Vancouver Island, British Columbia, Canada. Pages 217–221 in: C. R. Veitch, M. N. Clout & D. R. Towns (eds) Island invasives: eradication and management. , IUCN, Gland, Switzerland.
Supporting evidence from individual studies
A replicated, before-and-after study in 2004–2007 of 12 ponds in California, USA (D’Amore, Kirby & McNicholas 2009) found that there was a significant increase in adult California red-legged frogs Rana draytonii in ponds in the two years after American bullfrog Rana catesbeiana removal. Counts increased from eight to 11 frogs in removal ponds. Numbers did not change in control ponds. Adult frogs were less visible when bullfrogs were present. Frogs used willows significantly less as cover, and were found on bare shores twice as much when adult bullfrogs were absent. Invasive American bullfrogs were removed from 12 ponds in 2004–2007. They were captured by hand, Hawaiian slings (spears) and seine netting (for tadpoles). Six ponds without bullfrogs in an adjacent field were monitored for comparison. Amphibians were monitored three times each week until October 2007.
A before-and-after study in 2008–2011 of leopard frogs in Arizona, USA and Mexico (Sredl et al. 2011) found that eradication of bullfrogs Rana catesbeiana resulted in an increase in range of chiricahua leopard frogs Lithobates chiricahuensis and lowland leopard frogs Lithobates yavapaiensis. Surveys in 2010–2011 showed that chiricahua leopard frogs had dispersed into eight and lowland leopard frogs into three sites that had previously been unsuitable due to presence of bullfrogs. Chiricahua leopard frogs dispersed over 8 km to a site further north than it had recently been documented in the region. Bullfrogs were eradicated between 2008 and 2010.
- D’Amore A., Kirby E. & McNicholas M. (2009) Invasive species shifts ontogenetic resource partitioning and microhabitat use of a threatened native amphibian. Aquatic Conservation: Marine and Freshwater Ecosystems, 19, 534–541
- Sredl M.J., Akins C.M., King A.D., Sprankle T., Jones T.R., Rorabaugh J.C., Jennings R.D., Painter C.W., Christman M.R., Christman B.L., Crawford C., Servoss J.M., Kruse C.G., Barnitz J. & Telles A. (2011) Re-introductions of Chiricahua leopard frogs in southwestern USA show promise, but highlight problematic threats and knowledge gaps. Pages 85-90 in: Global Re-introduction Perspectives: 2011. More case studies from around the globe. IUCN/SSC Re-introduction Specialist Group & Abu Dhabi Environment Agency, Gland, Switzerland.