The impact of sett disturbance on badger Meles meles numbers; when does protective legislation work?

Abstract

Considerable increases in badger Meles meles numbers have been reported from long-term studies on local populations and national surveys in Britain. One theory proposed to explain this population change, is that increased protective legislation has led to reduced levels of persecution, allowing the population to expand. In the present study, we show that the badger population in Northern Ireland has not increased in parallel with the British population, and investigate whether sustained high persecution levels are responsible. As legal protection of badgers in Northern Ireland was not increased at the same time as in Britain, a simultaneous decrease in persecution would not be expected. We test two hypotheses: (i) where there is no change in the level of sett disturbance, the number of social groups will remain unchanged and, (ii) if sett disturbance affects group size, those groups suffering from most disturbance will be smallest. We demonstrate that badger sett disturbance affects both social group size and the number of social groups, thus influencing overall badger density. We also show that high levels of sett disturbance are constraining the growth of the Northern Ireland badger population and discuss what lies behind the apparent failure of the protective legislation in this country.