Estimating population size by genotyping remotely plucked hair: the Eurasian badger.
Size is a basic attribute of any population but it is often difficult to estimate, especially if the species under investigation is rare or cryptic. For example, there is currently no cheap and robust way of estimating the abundance of the European badger Meles meles, despite the species' role as an agricultural pest and carrier of bovine tuberculosis. We tested the reliability and accuracy of estimating badger abundance by genotyping DNA extracted from remotely plucked hair. We assessed the accuracy of our methodology by estimating local abundance by direct observation. Hair samples were collected near five target setts using a baited barbed wire enclosure or (at one sett) barbed wire suspended over a clearly visible badger run. All the hairs found on a barb were included in the extraction. Of the 113 samples collected over a 6-month period, 105 gave rise to amplifiable DNA and originated from single animals. Through comparison with reliable reference genotypes of captured badgers, we showed that amplifiable DNA, including extracts obtained from single guard hairs, produced accurate profiles in a single round of amplifications. Direct observation of the target setts suggested that a minimum of 13 badgers was present in the study area. Analysis of the 105 usable samples provided a baseline estimate of 15 animals. To test the practical use of hair trapping to estimate population size, hair samples were collected daily during a 3-week period. The 66 usable samples obtained originated from 14 of the 15 known badgers. Estimates of true abundance were generated using rarefaction analyses, the least biased of which produced an abundance estimate of 14.23, corresponding well with the number of genetic profiles obtained over the 6-month period. The results allowed comparisons of theoretical predictions and empirical data relating to rarefaction analyses. Synthesis and applications. DNA extracted from remotely plucked badger hair could form the basis of a potentially cost-effective, reliable and widely applicable method of estimating badger abundance. Hair trapping may offer a feasible method of estimating population size in a range of species even when the species are rare or patchily distributed.