Sir

In News and Views (“Ethics and amphibians” Nature 431, 403; 2004), Robert M. May discusses a study by M. A. McCarthy and K. M. Parris on the effects of toe-clipping on amphibians. This is a standard technique for uniquely marking animals in ecological research (see guidelines at http://www.asih.org/pubs/ASIH_HACC_Final.pdf ). McCarthy and Parris show that return rates decreased as the number of toes clipped increased in four frog species; they and May raise ethical and practical questions about the technique. There is, however, a fuller picture to be considered.

Several studies have found no negative effects of toe-clipping. McCarthy and Parris suggest that this may be due to low statistical power, but this has not been shown in all cases in which no effect was observed (see, for example, J. J. van Gelder and H. Strijbosch Amphibia-Reptilia 17, 169–174, 1996; and J. A. Ott and D. E. Scott J. Herpetol. 33, 344–348, 1999). Effects of toe-clipping evidently vary among species and so must be assessed accordingly.

Alternative marking techniques often cannot be used. Many adult frogs are less than 20 mm long, as are juveniles of larger species. The smallest passive integrated transponder (PIT) tags are about 10 mm long, too large for small frogs. Many species cannot be marked using other approaches, such as elastomers, alphanumeric tags or freeze-branding, and do not have consistent, identifiable markings.

Other techniques may have worse effects, as M. Schlaepfer has shown (Herpetol. Rev. 29, 25–26; 1998). Implantation of PIT tags often involves surgery on the body cavity; even implantation under the skin carries a risk of more serious infection than in an extremity. Many ecological studies require trading the risks of a marking technique against the gains in understanding. More research evaluating these risks is needed.

Far from acting with ‘casual barbarity’, biologists who use the toe-clipping technique do so after considering alternative techniques and with the approval of institutional animal care and use committees. The resulting data are essential for managing threatened populations, as well as for other purposes: toe clippings are sources of DNA for genetic studies, and act as samples for identifying the diseases implicated in catastrophic amphibian declines.

We believe it is less ethical to sit back and watch species slip into extinction than it is to use the best available methods to help to conserve them.