Survival rates and causes of mortality in black grouse Tetrao tetrix at Lake Vyrnwy, North Wales, UK.
Rates of survival and reproductive success in black grouse Tetrao tetrix were assessed during a four-year study at Lake Vyrnwy in North Wales between 1999 and 2003. We used radio-tracking to assess survival rates of 33 individuals. The juvenile (September-February) survival rate was 0.18, compared with 0.66 over the same time interval for adults. Predation by raptors accounted for almost 2/3 of deaths. Broods were surveyed using pointer dogs in late August. Reproductive success was low, averaging 1.0 chicks/hen. Recruitment into the breeding population was insufficient to balance the observed mortality rates, resulting in a 67% decrease in breeding adults during the four-year study. This happened despite the likely immigration into the study area of dispersing juvenile females from adjacent areas with higher breeding success. An equivalent reduction in the abundance of red grouse Lagopus lagopus scoticus was observed, and this was also associated with years of low breeding success. Management methods that both reduce the impact of raptors on juvenile black grouse survival and improve breeding success are probably required to conserve black grouse in Wales.