Further declines of the Western Capercaillie Tetrao urogallus in Scotland as shown by the 2021-2022 winter survey

Capsule: The estimated number of Western Capercaillies Tetrao urogallus in Scotland in winter 2021-2022 was 532 with a 95% confidence interval (CI) of 227-810.Aim: To produce an updated estimate of the number of Western Capercaillies in Scotland.Methods: Line transects were surveyed across the current distribution, sampling in two separate strata: a primary stratum in the core range and a secondary stratum in peripheral areas. Multi-covariate distance sampling was used to fit alternative detection functions to the sighting data, deriving national, regional and sex-specific estimates of abundance.Results: The survey recorded 115 Western Capercaillies in 104 separate encounters across 635 transects, yielding a population estimate of 532 individuals (95% CI: 227-810). This estimate was 52% lower than from the population survey in 2015-2016 (1114 individuals, 95% CI: 805-1505). Declines were greater for females than for males, leading to an adult sex ratio in favour of males. Most of the population (80%) continues to be concentrated in the region of Badenoch and Strathspey.Conclusion: With the population at its lowest level since the start of national monitoring in 1992-1994, the likelihood of extinction in Scotland for a second time seems inevitable without a step-change in conservation action. Measures to improve breeding success and survival are needed and should be targeted in the core of the range to maximize impact on the population.

Automated summary

The estimated number of Western Capercaillies in Scotland in winter 2021-2022 was 532, which is 52% lower than the estimate in 2015-2016. The majority of the population is concentrated in Badenoch and Strathspey region. With the population at its lowest level since monitoring began in 1992-1994, measures are urgently needed to improve breeding success and survival.