Fission-fusion dynamics and spring movements in first-year carrion crows Corvus corone challenge the efficiency of culling strategies.

This study investigates the spatial behaviour and social dynamics of immature carrion crows (Corvus corone) caught in Paris, with the objective of discussing the efficiency of current culling strategies used to mitigate crop damage. Using GPS tracking data from 80 first-year crows of four different cohorts, we characterized seasonal variations in movement, roosting behaviour, and fission-fusion spatial dynamics. Results show that young crows remain closely associated with their natal sites until March of the year following hatching, after which they disperse to urban, peri-urban and rural areas, particularly in April and May, with peak daily movement distances averaging 2.7 km. This period coincides with the sowing of sensitive crops such as maize and sunflower, during which culling campaigns are often conducted. Furthermore, we document fission-fusion dynamics, with fluid group associations centred around predictable anthropogenic food sources and communal roosts, certainly facilitating repeated interactions and social learning. These findings suggest that current culling practices, largely targeting transient juveniles, are unlikely to achieve long-term reductions in population size or crop damage. Instead, the study highlights the importance of addressing particularly anthropogenic food availability as a potentially more effective and ethical strategy for managing urban, peri-urban and even rural crow populations.