Microhabitat Selection in Ground-Nesting Birds

Abstract

Ground-nesting birds are among the most rapidly declining vertebrate groups in European agricultural and grassland landscapes, with nest predation and habitat degradation acting synergistically to reduce reproductive success below population replacement levels. This study characterised microhabitat selection at nest sites versus random available locations for eight ground-nesting farmland and grassland bird species (Vanellus vanellus, Gallinago gallinago, Tringa totanus, Alauda arvensis, Anthus pratensis, Motacilla flava, Crex crex, and Numenius arquata) across 84 sites in Sweden, Germany, and the Netherlands, monitoring 1,284 nests over four breeding seasons (2020-2023). Logistic regression and compositional analysis identified sward height (mean 12.4 +/- 3.2 cm at nest sites), vegetation cover at nest entrance (mean 68.4 +/- 8.4%), bare ground proportion within 2 m radius (mean 24.8 +/- 6.4%), and distance to nearest tall vegetation (mean 14.8 +/- 4.2 m) as the strongest predictors of nest site selection across species. Nest survival analysis (logistic exposure method) demonstrated that microhabitat variables explained 48.4% of variance in daily nest survival probability, with nests in optimal microhabitat (sward height 10-15 cm, cover 60-75%, bare ground 20-30%) showing 2.84-fold higher daily survival probability than nests in suboptimal microhabitat. Livestock grazing intensity was the primary landscape driver of microhabitat availability, with extensively grazed pastures providing optimal microhabitat for 6.4 +/- 1.2 species simultaneously versus 2.4 +/- 0.8 species in intensively managed grasslands. These findings provide quantitative, species-specific microhabitat targets for agri-environment scheme design under the EU Common Agricultural Policy.