Estimation of badger abundance using faecal DNA typing

1. Wildlife management and conservation programmes often require accurate information on population density, but this can be difficult to obtain, particularly when the species in question is nocturnal or cryptic. Badger populations in Britain are of intense management interest because they are a wildlife reservoir host of bovine tuberculosis (TB). Attempts to manage this infection in badgers, whether by population control or vaccination, require reliable methods of estimating population size. In addition, such estimates are also required to support research into badger ecology and TB epidemiology. Currently, the most accurate estimates of local badger population size are obtained from labour-intensive and time-consuming mark-recapture studies. 2. In recent years, DNA has been successfully extracted from the faeces of certain mammals, and used to generate a genetic profile of the defecating individual. Here we report on an application of this technology to estimate badger abundance. 3. Faecal samples were collected on 10 consecutive days from every freshly deposited dropping at latrine sites close to occupied setts in three badger social groups. Badger DNA was extracted from 89% of samples, and 20 different individuals were reliably identified. The genotypes derived from the faecal samples were compared with those obtained from blood or samples from badgers live trapped at the same setts. 4. The faecal genotypes from badgers with known trap histories revealed that latrines were used equally by males and females, and by badgers ranging in age from cubs (< 1 year old) to 9 years old. Individual badgers used the latrines on between one and six different nights. Rarefaction analysis produced abundance estimates that closely matched those obtained from live trapping. 5. Synthesis and applications . Systematic sampling and genetic typing of fresh faeces from badger latrines can provide data that can be used to estimate abundance accurately. This approach requires considerably less human resources than repeated live trapping and mark-recapture. The technique may be valuable for future badger research and management in relation to bovine TB, where accurate estimates of abundance at a local scale are required.