Habitat and other environmental correlates of the decline of breeding Whinchats Saxicola rubetra in the UK since the mid-1990s

Abstract

ABSTRACT Capsule Declines in Whinchat Saxicola rubetra breeding abundance in the UK vary with habitat and other environmental conditions. Aims To test for associations between changes in Whinchat abundance between 1994 and 2018 and measures of habitat and environmental conditions on UK breeding sites. Methods Whinchat counts collected through a national monitoring scheme were tested at coarse 1 km2 square and finer 200 m transect scales against habitat data collected in 2017/2018, plus remotely sensed data to test for long-term change. Results At the 1 km2 square scale, mean change in Whinchat abundance was more negative where woodland occurred more frequently, and at more northerly latitudes. Rates of decline were lower where there was greater cover of Purple Moor-grass Molinia caerulea and non-bracken vegetation height was taller. At the finer 200 m transect scale, more closely resembling Whinchat territory size, rates of decline were greatest in areas dominated by human sites, woodland, and enclosed farmland, compared to unenclosed open semi-natural habitats; however, within the latter category, declines were lower in grass-dominated relative to heather-dominated habitats. Rates of decline were also lower closer to valley bottoms, with greater Bracken Pteridium aquilinum cover and at mid-elevations (300 m), and greatest where there was greater cover of bare ground and trees, and moderate cover of grasses (excluding Molinia and Lolium spp.). The strength of the finer-scale associations varied between dominant habitat types. Whinchat abundance was lower where a remotely sensed index of vegetation productivity (normalized difference vegetation index [NDVI]) was higher, and abundance change more negative where temporal increases in NDVI were greater. Conclusion Unenclosed semi-natural grassland showed the lowest rate of decline and offers the best opportunities to conserve Whinchats. Woodland expansion is likely to have a detrimental impact on breeding Whinchats. Future research should investigate how important habitat and environmental correlates influence key demographic rates affecting recruitment.