Dispersal, survival and causes of mortality in black grouse Tetrao tetrix in northern England.

Abstract

Between autumn 1998 and spring 2000, 70 black grouse Tetrao tetrix (48 poults and 22 adults) were equipped with radio transmitters in the North Pennines, England. We recorded timing and distances of dispersal, survival rates and causes of death. First-year survival rates differed between years, but in each year were highest in late autumn prior to dispersal, when predation by stoats Mustela erminea and raptors accounted for three-quarters of deaths. First-year grouse survival was lower than that of adult birds owing to predation in the autumn and winter by raptors and stoats. The annual adult survival rate of 0.72 was higher than those found in most other European studies. By contrast, breeding success was low. Dispersal was confined to first-year hens, with distinct dispersal periods in late autumn (mean 10.3 km) and again in early spring (mean 5.8 km). Natal dispersal resulted in none of the first-year hens breeding within the study area. Adults of either sex and first-year cocks showed high site fidelity. This has practical repercussions when considering prescriptive management to aid species recovery and range expansion in relation to habitat fragmentation at both the local and regional levels.