Abundance of male Black Grouse Tetrao tetrix in Britain in 2005, and change since 1995-96

Abstract

Capsule: There was a non-significant decline in the number of displaying males in Britain between 1995-96 and 2005, with a significant decline in Scotland. Aims: To estimate the number of displaying male Black Grouse in Britain in 2005, and to compare this with the 1995-96 estimate. Methods: Surveys were carried out in a stratified sample of 1-km (Wales) and 5-km (Scotland and England) squares throughout the known range, using similar methods to the 1995-96 survey. Results: There were an estimated 5078 displaying males in Britain in 2005 (95% CI 3920-6156). This estimate is 22% less than the 1995-96 estimate of 6506, although these estimates are not significantly different. In Scotland, numbers fell by 29% overall, comprising large and significant declines of 49% and 69% in southwest and southeast Scotland, respectively, but small and non-significant declines in north (16%) and northeast Scotland (9%). In England, there was a non-significant decline of 11%, while in Wales numbers rose by 39%. Where numbers have declined there has been a decrease in the number, but not the size, of display groups. Display sites in Britain were at higher altitudes (median 400 m) in 2005 than in 1995-96 (median 340 m). Conclusion: Although Black Grouse numbers in Wales increased, this survey provides evidence of a large decline in southern Scotland. The causes of this decline are not fully understood, and further research is urgently required to reveal the underlying mechanisms and implement appropriate conservation measures. © 2008 British Trust for Ornithology.