Abundance and distribution of capercaillie Tetrao urogallus in Scotland 1992-1994

摘要

The capercaillie Tetrao urogallus L. is a cryptic forest gamebird which has decreased in Scotland, as in much of its range, since the 1970s. Despite previous surveys of the bird's range in Scotland, there was no assessment of numbers giving confidence limits. Here we establish such a baseline against which future estimates may be set. Numbers were estimated from a combination of questionnaires, Geographical Information System (GIS) and advanced line transect techniques, using repeatable methodology which should be applicable to other cryptic forest species. The GIS was used to map capercaillie distribution and relative abundance in Scotland. Transects were then placed randomly within the bird's reported range, stratified by geographical region and estimated abundance rating. From observations on 426 2-km line transects in winters 1992-1993 and 1993-1994, the population was estimated to be 2200 birds (1500-3200, 95% C.L,) There were approximately twice as many females as males in the sample. Birds were present from the Forth-Clyde industrial belt northwards to the Dornoch Firth and from the Central Highlands eastwards. The main centres of population were in eastern and central Scotland (Deeside, Speyside and Perthshire). The highest densities were in native pinewoods (2.7-5.0 birds km~(-2)), and the lowest were in thicket and pole/high canopy plantations (0.4-0.9 birds km~(-2)). This information is being used to identify sites for enhancing capercaillie habitat under the Forestry Authority's Woodland Grant Scheme.