Coarse and fine scale habitat associations of breeding SkylarksAlauda arvensisin the UK

The occurrence of breeding Skylarks, in terms of both density and presence/absence, was assessed from Breeding Bird Survey data in relation to habitat in a random sample of about 1500 1-km squares throughout the UK in two consecutive years, with particular emphasis on the farmland habitat. Upland grassland and other seminatural grassland habitats held the highest mean densities of Skylarks. Within farmland, arable land held the highest and pasture land the lowest densities, but there was a seasonal decline in arable density. Regression analyses showed that Skylark occurrence was most consistently related to the area of arable farmland (positive effects) and the area of woodland (negative effects). Skylark density increased with increasing habitat diversity in upland squares only. Within farmland, boundary characteristics and the presence of grazers had the most consistent negative effects. The diversity of field types was positively related to Skylark density, which gives some support to the hypothesis that a decrease in the diversity of field types as a result of simplification of farm rotations in recent decades may have led to the decline of the Skylark in the UK, but further conclusions about the effects of specific crop types were not possible at this scale of analysis.