Temporal segregation and coexistence between the Lanner Falcon Falco biarmicus and the Western Barn Owl Tyto alba in a shared secondary cavity in a cliff

Temporal segregation between diurnal and nocturnal raptors is a well-known ecological principle, yet it has rarely been documented with direct, continuous observations in shared nesting environments. In this study, we provide one of the first camera-trap based documentations of such segregation between the Lanner Falcon and the Western Barn Owl using the same secondary cavity in a cliff in eastern Sicily (Italy). Using automatic camera traps installed inside the cavity, we collected 785 video recordings between April and June 2025, yielding 547 detection events for the Lanner Falcon and 197 detection events for the Western Barn Owl. The analysis of diel activity patterns revealed an almost complete temporal separation (Δ = 0.043; 95% CI: 0.036–0.049) between the strictly diurnal Lanner Falcon and the nocturnal Western Barn Owl. Since the Western Barn Owl is occasionally preyed upon by the falcon, this near-complete temporal separation prevents direct encounters and is consistent with predation risk reduction. Our findings illustrate how pre-existing differences in daily activity timing – inherent to the respective chronotypes of each species – can allow a predator and a potential prey to exploit the same physical refuge without direct encounters, thereby increasing the ecological diversity of cliff ecosystems.