Clarifying the effect of toe clipping on frogs with Bayesian statistics

Summary 1. Toe clipping is commonly used in population ecology to identify individual amphibians, particularly frogs and toads. Toe clipping may influence the return rate of the marked animals, although results of previous studies have appeared to be contradictory. 2. We re-analysed available data using Bayesian statistics to examine how the return rate of frogs may change with the number of toes removed. 3. Our re-analysis indicated that toe clipping reduces the return rate by 4‐11% for each toe removed after the first, assuming the effect is the same for all toes. 4. A second analysis allowed the effect of removing each toe to change linearly with the number removed. This indicated that when one toe had already been removed, the return rate was reduced by 3·5% (95% credibility interval of 0‐7%) upon removal of a second. The reduction in return rate on removal of an additional toe was 30% (95% credibility interval of 20‐39%) when seven toes had already been removed. 5. When considering the cumulative effect of toe clipping, the return rate of frogs with two toes removed was estimated to be 96% of those with one toe removed. This ratio decreased to 28% for frogs with eight toes removed. 6. Synthesis and applications. We found that the effect of toe clipping on the return rate of amphibians increases with the number of toes removed. Because this effect is reasonably consistent among studies, the estimated impact should be recognized in future work that uses toe clipping to estimate population sizes and survival rates. In addition, our study has important implications for the ethical treatment of animals, the continued use of toe clipping to mark species of conservation concern, and the removal of multiple toes from an individual frog or toad.

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