Variations in the vital rates of black grouse Tetrao tetrix in the United Kingdom.

Abstract

In the United Kingdom, black grouse Tetrao tetrix are in severe decline with only 6,500 displaying males in 1995-1996 and a range retraction of 28% between 1972 and 1991. Recent declines have been greatest in central and southern Scotland and parts of Wales and contrast with relative stability in northern England. We compare the demography of black grouse in three regions: North Wales, northern England and the Scottish Highlands. Patterns in annual fecundity, measured as fledglings per breeding female, were correlated between regions, suggesting that annual weather patterns common across regions may be a key determinant of breeding success. Site related effects such as habitat quality or management were also significant in northern England and North Wales. Male population growth rates at leks were positively correlated with fecundity in the previous year. Fecundity was highest in North Wales and the Scottish Highlands at 1.7 chicks per female in August compared to 1.3 in northern England. Variations in the annual fecundity of radio-tagged females were linked to differences in brood survival rather than clutch survival, which did not differ among years. We found a non-significant trend for juvenile survival to be lower in North Wales (0.18) than in either northern England (0.65) or the Scottish Highlands (0.56). Similarly, annual adult survival also tended to be lower in North Wales (0.44) than in either northern England (0.70) or the Scottish Highlands (0.66). Predation was the main cause of death in all regions, with red fox Vulpes vulpes and raptors being the chief predators in North Wales and the Scottish Highlands and stoat Mustela erminea in northern England. The last 10 years have seen the implementation of a series of black grouse recovery projects in the UK. An understanding of the limiting demographic stage in each project area is critical before appropriate remedial management prescriptions can be implemented.