Impact of recent changes in agricultural land use on farmland bird trends

Abstract

Agriculture has been, and still is, strongly shaping landscapes across Europe. In recent decades, agricultural land use has changed considerably, mainly driven by reforms of agricultural and bioenergy policies. Here, we related temporal and spatial changes in agricultural land use at both the landscape and regional scale to population trends of farmland birds. Monitoring data of the Common Breeding Bird Survey of Lower Saxony, Germany, and high-resolution data on agricultural land use from 2005 to 2012 were used to calculate the temporal trend slopes of farmland birds and agricultural variables at the landscape scale (1km2). Agricultural variables comprised the area covered by maize, set-aside, permanent grassland as well as crop diversity. The number of territories were analysed for all farmland birds together as well as for two subgroups (‘field nesters’ and ‘non-field nesters’). Further, we tested whether population trends of farmland birds differed between agricultural regions, characterised by different land-use change dynamics.Trends of farmland birds and non-field nesters were negatively related to increasing maize cultivation at the landscape scale. We further found that population trends of field nesters reacted region-specifically and performed worst in an agricultural region that was characterised by the strongest increase of maize and decrease of crop diversity, indicating a negative effect of broad-scale landscape homogenisation. To counteract the process of spatial and temporal land-use homogenisation and to inform policy-makers on options for mitigation, we conclude that conservation actions should be tailored at a regional scale to halt or even reverse negative farmland bird population trends.