Badgers are among Europe's most endangered mammals. For effective conservation and understanding their role in transmitting bovine tuberculosis detailed knowledge of their reproductive and social system is essential. But so far little is known about their reproductive biology. This will be the first study concentrating on behavioural changes of individual females in relation to their reproductive state. Female behaviour will be observed by radiotracking and IR-light sensitive video cameras. The main sett area above ground will be video-monitored continuously and very small cameras will be installed inside the dens. As badgers were never observed before in their natural dens, these recordings will provide new insights in their social life and reproductive behaviour. New non-invasive methods will be applied to quantify levels of sex-hormones and corticosteroids in faeces to determine the reproductive state (oestrus-cycle/gravidity) and levels of social stress in breeding and nonbreeding females, thus investigating the mechanisms of reproductive suppression.