Removing a unique combination of toes in frogs and toads is a common way for ecologists to ID individuals. Experimenters have assumed that this is harmless. But now, a study in the August issue of the Journal of Applied Ecology shows otherwise: The more toes gone, the less likely a marked frog is to ever hop into sight again.
Ecologists Michael McCarthy and Kirsten Parris of the Royal Botanic Gardens Melbourne in Australia used a sophisticated statistical technique called Bayesian analysis to check for effects of toe clipping on frog and toad survival. Six colleagues gave them their records for a total of almost 3700 toe-clipped individuals of two species of frog, one from Australia and one from South America, and a North American toad species. McCarthy and Parris then looked at the number of toes removed to create each animal's digital code, and whether or not it was ever seen again.
The results were clear-cut: With each additional toe missing, an animal's chances of recapture dropped. An individual missing eight toes was almost one-fourth as likely to be retrieved as one with only one toe gone. The researchers suspect that the missing animals die from infection, although other explanations are possible; for instance, the maltreatment could make them flee the study area. Either way, McCarthy says, the new findings show that toe clipping hurts the animals and can potentially lead to biased results. Unfortunately for researchers and their subjects, he says, there are no satisfactory alternative marking techniques.
Evolutionary biologist Richard Shine, who works on amphibians and reptiles at the University of Sydney, Australia, is put in a quandary by the new study. He points out that toe clipping is used by conservation ecologists to study populations of endangered amphibians. Now that the technique itself may be harming the animals, he says, it is doubtful that an "animal ethics committee ... would allow a researcher to chop toes off willy-nilly."
Froglog Newsletter subscribers debate toe clipping amphibians here ...
... and here
U.S. National Wildlife Health Center's page on toe clipping
National Academies Press page on alternative marking systems for amphibians