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

ABSTRACT

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.

Acknowledgements

We thank Dr Sue Haysom (NatureScot), Colin Edwards (Scottish Forestry) and Carolyn Robertson of the Cairngorms Capercaillie Project. We thank everyone who has submitted Capercaillie sightings. We also thank Dr Laura Marshall of the Centre for Research into Ecological and Environmental Modelling, University of St. Andrews, for advice on survey design, which was based on the original design of Prof. Steve Buckland. The field work was carried out by Ewan Craig, Rhys Findlay-Robinson, James Gordon, Stephanie Griffiths, Elizabeth Holmes and Alex Starace, with additional help from Lois Canham, Mick Canham, Helen Gray, Christopher Tilbury and two of the authors (Dr Steven Ewing and Nicholas Wilkinson). Emma Teuten in the Conservation Data Management Unit of the RSPB produced field survey maps. The brood count data featured in this paper have been provided by the Game & Wildlife Conservation Trust. We are grateful to Prof Jennifer Smart, Claire Smith (RSPB), Dr Robert Moss and an anonymous reviewer for constructive comments which improved earlier drafts of this manuscript. We thank the many landowners, factors, foresters and gamekeepers who helped with access to sites.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This survey was funded by the Cairngorms National Park Authority, Forestry and Land Scotland, NatureScot, Scottish Forestry and the Royal Society for the Protection of Birds.