Nest predation and the influence of habitat structure on nest predation of Wood Warbler Phylloscopus sibilatrix, a ground-nesting forest passerine

Increasing rates of nest predation is one of several hypotheses proposed to explain observed declines of Wood Warbler Phylloscopus sibilatrix populations in the UK. Nest predation may be influenced by how nest concealment is affected by vegetation structure, which may vary between breeding sites. Detailed nest monitoring within three study areas with varying population trends identified the main nest predators and predation as the main cause of nest failure. Comparison of habitat structure surrounding nests with non-nest locations within territories showed that nests were placed on steeper slopes, in areas with a taller canopy, intermediate understorey density, greater cover of bramble and intermediate cover of tall field layer vegetation. Predation rates were related to field layer structure with lower predation rates associated with greater cover of medium-height vegetation. However, the size of the effect of vegetation on predation rates was small, and vegetation management is unlikely to have a strong impact on predation rates except in extreme cases of very low ground cover.