Field, landscape and regional effects of farmland management on specialist open-land birds: Does body size matter?

Farmland birds have suffered significant declines in the last decades due to agricultural intensification. Agri-environment schemes (AES) aim to reverse this process by promoting “nature friendly” practises at the field-scale. AES based on the habitat requirements of target species have usually been successful, but the concurrence of species groups with contrasting habitat requirements (guilds) makes the design of successful measures for the whole bird community difficult. The effectiveness of AES is also constrained by landscape and regional effects not addressed by its field-scale application. Effects acting at different spatial scales could differ among bird species depending on basic life-history traits such home range size and landscape perception, which should covary with body size. We are not aware, however, of any study which investigates whether relative effects at different spatial scales could vary predictably within bird guilds. We analyse whether relative effects of within-field (including AES application), landscape and regional factors on open-land birds differ according to body size. Large birds were mostly affected by regional and landscape factors, whereas for small birds landscape and within-field factors were important. Hence, relative effects at changing spatial scales showed predictable variation according to bird size within this endangered and specialised farmland guild. These size-dependent effects should be taken into account for the design of more effective, integrated multi-scale strategies for the conservation of farmland birds.