Agri-environment scheme prescriptions and landscape features affect taxonomic and functional diversity of farmland birds

Abstract Agri-environment schemes (AES) are a major conservation tool for protecting declining farmland birds in Europe. Most studies evaluate AES effectiveness on taxonomic diversity but there is a knowledge gap about how AES affect functional responses. We evaluate the effects of different AES on taxonomic and functional responses of open-land and overall farmland birds in extensive cereal croplands of Spain. Specifically, we analyse how the proportion of food to shelter prescriptions and landscape features (length of field boundaries and proportion of herbaceous crops) influence AES effectiveness by comparing the response of bird diversity in AES-managed and paired control fields. We found that increased proportion of food prescriptions increased species richness and Shannon diversity of birds whereas balanced AES (similar proportion of food and shelter prescriptions) increased their abundance. AES with more food prescriptions also led to increased functional diversity of diet plasticity and wingspan for open-land birds. The functional diversity of diet plasticity in all bird species and of habitat specialisation in all and open-land birds increased with balanced AES in control fields but remained unaltered in focal fields with variation in the proportion of food to shelter prescription. This suggests that AES application reached maximum effects for these traits in focal fields independently of prescription types and further landscape-level benefits of the promotion of shelter in AES-managed fields. Overall, the length of field boundaries increased taxonomic and functional diversity of birds while the proportion of herbaceous crops decreased them. Both landscape variables showed non-linear relationships, fitting predictions from the landscape complexity-local diversity hypothesis. Our findings indicate ways to improve AES effectiveness for both traditional and new relevant conservation goals and encourage the evaluation of functional diversity in AES monitoring.