How can rook phenology and crop damage be linked?

The rook (Corvus frugilegus) can cause damage to maize and sunflower at the seedling stage. Little is known about the agronomic and ecological factors influencing the depredation behavior. This study examines how the phenology and movements of rooks, in relation to crop development, influence the scale of damage to maize and sunflower seedlings.,A field study was conducted across a network of crop fields in the Paris Basin (sunflower, n=177; maize, n=109). Damage was recorded and farmer surveys were used to record sowing dates and use of repellent seed coatings. Simultaneously, adult male rooks were GPS-tracked over two years to monitor spring movements, while breeding phenology was documented through direct observation of rookeries.,Two successive movement patterns were identified, with a transition date corresponding to the fledging period. After this period, rooks made longer daily foraging trips further away from the rookery. These changes in foraging movements combined with phenological chronology and the distance from field crops to the nearest rookery, were used to develop a spatio-temporal typology of damage risk. Analysis of damage data based on this risk categorisation showed that fields within a 4 km radius of rookeries were more frequently damaged. Beyond this distance, damage depended on crop sensitivity during the fledging period; specifically, fields with early-sown crops were less affected. Additionally, maize seeds coated with a repellent suffered less damage.,To mitigate rook damages, our results suggest two strategies: sowing early when the field is far from the rookery and enhancing its protection when it is nearby.