Varying potential of conservation tools of the Common Agricultural Policy for farmland bird preservation.

Agri-environment schemes (AES) and greening of the Common Agricultural Policy (CAP) are crucial tools for biodiversity conservation in Europe. However, they have not been associated formally to any performance monitoring program that supports their actual benefits for biodiversity, and their effectiveness is recurrently questioned. We present an extensive evaluation of the potential of CAP conservation tools to support farmland bird diversity throughout the most representative cereal regions in Spain. We explore bird diversity responses to AES application in pairs of cereal plots with and without AES. We also explore bird responses to a set of habitat indicators, both of productive (farmed) and semi-natural components (i.e., field margins and natural vegetation remnants), within plots and in the surrounding landscape. We use these habitat indicators as proxies of distinct greening measures (e.g., hedges, fallow, crop diversification). Our results point at the prospective success of measures focused on promoting, particularly at landscape scales, certain productive habitats (e.g., fallow land and legume crops), mainly but not exclusively for open land birds. Promoting semi-natural habitats (both areal and linear elements) also resulted positive, primarily for forest and ecotone birds, but also open land birds. Our results evince high variability in the capacity of AES and distinct greening measures to support bird diversity among regions and groups of birds. More regionally-targeted conservation measures (i.e., focused on specific requirements of targets, considering explicitly regional species pools and landscape constraints) are thus required. These measures could be assembled in the new CAP by means of compulsory measures applied throughout the agricultural landscape (i.e., advanced environmental conditionality likely replacing cross-compliance and greening) and voluntary instruments (i.e., eco-schemes and AES) with enough farmers' uptake that ensures its impact at landscape scale. Performance evaluation and subsequent adaptation based on the results obtained ought to accompany the implementation of conservation tools.