Do skylarks prefer autumn sown cereals? Effects of agricultural land use, region and time in the breeding season on density

Explanations for causes of farmland biodiversity declines often assume no spatial or temporal variation in the effects of land use on species abundance and performance. For example, European populations of skylark are assumed to have declined partly due to the switch from spring sown to autumn sown crops. Still, land use preferences of farmland birds may vary with region, landscape structure and time in the breeding season. We inventoried 430 transects in 36 landscape plots (each 25 km2) in three major agricultural regions of southern Sweden and show that land use-specific densities of skylarks display strong temporal and regional differences. Pre-nesting densities in late April–early May were highest in autumn sown cereals and other arable land use with vegetation, but decreased during the course of the breeding season such that densities in spring sown cereals were slightly higher than those in autumn sown cereals late in the season. This temporal shift in crop-specific densities of skylarks differed between regions. Temporal patterns of crop-specific densities of skylarks could be explained in terms of vegetation-dependent nest predation risk and foraging conditions. We suggest that land use preferences of farmland birds often could be expected to display a temporal and spatial variation and this should be reflected in a more flexible, context-dependent approach for the conservation of farmland biodiversity.