Capercaillie Tetrao urogallus abundance and habitat use in Scotland, in winter 1998-99

Capsule A second full survey in which we estimate the population at 1073 birds (95% CL 549-2041). Aims To provide an up-to-date estimate of the population size of Capercaillie in Britain and to identify habitat use by Capercaillie in winter. Methods Using the census technique of distance sampling, flushed birds were counted along line transects walked in stratified random blocks of forest within the species' range. The same transects were surveyed as used in the 1992-94 survey, enabling direct comparison of the results. Densities were estimated using the DISTANCE program, combining these data with those from a similar survey of Capercaillie in 1992-94 to allow a more robust estimate of the detection function. Results The Capercaillie population was estimated to be 1073 birds (95% CL 549-2041). This represents a decline of 51% between the two surveys, at a rate of 13% per annum. Females declined at a faster rate than males resulting in a marked change in the sex-ratio, which was close to I: I for the entire population. Bird densities declined by a similar magnitude in both native pinewoods and other woodlands in comparison to 1992-94. Even so, densities were significantly higher in native pinewoods (1.63 km(-2)) than in other woodlands (0.43 km(-2)), which comprised largely planted Scots Pine Pinus sylvestris, larch Larix spp., Lodgepole Pine Pinus contorta and Sitka Spruce Picea sitchensis. Overall, Capercaillie tended to use forest stands with a high proportion of Scots Pine and Blaeberry Vaccinium myrtilus; features that are typical of native pinewoods and old pine plantations. Conclusions The Capercaillie population has undergone a dramatic decline during the last five years. The decline has been greater for females and has occurred across habitats. This information is helping to focus efforts in securing the future for Capercaillie in Scotland, which has now become a major conservation challenge.