Remove or control invasive bullfrogs

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Study locations

Key messages

  • 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.


About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. 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.

    Study and other actions tested
  2. 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.

    Study and other actions tested
Please cite as:

Smith, R.K., Meredith, H. & Sutherland, W.J. (2020) Amphibian Conservation. Pages 9-64 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

Amphibian Conservation

This Action forms part of the Action Synopsis:

Amphibian Conservation
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What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

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