Breeding in natural nesting sites can improve the resilience of local Lesser Kestrel ( <i>Falco naumanni</i> ) populations to environmental changes

The identification of key habitats of threatened species and of extrinsic environmental factors that influence their resilience to human‐induced environmental changes are the foundation for the definition of conservation objectives. Using the presence and numerical abundance data collected in a long‐term survey (2000–24) of breeding colonies of Lesser Kestrel Falco naumanni in Sicily (southern Italy), we defined occupancy patterns (on a focal sample of 99 colonies) and estimated population size (on a regional sample of 198 colonies). Each colony was categorized according to covariates based on its landscape (lowland, highland) and location in natural (cliffs) or artificial (buildings) sites. Occupancy modelling highlighted the prevalence of higher, annually variable colonization rates compared with low, annually constant local colony extinction rates. The colonization rates of the natural highland sites have a magnitude equivalent to those of local extinction rates of the artificial lowland sites, implying that local extinction in lowland colonies is compensated by colonization of cliffs in highlands. Furthermore, highland natural sites tend to have higher occupancy rates than colonies located elsewhere on the island. Since 2000, the Sicilian population increased to a peak of 1365 estimated pairs in 2011, then decreased, halving in 2019. From 2020 to 2024, a new numerical growth is taking place, mainly in the highland population. The lowland population is currently limited by the collapse of the buildings in which they nest and by drought and heatwaves that reduce offspring survival, while the cliffs of the cooler and wetter highland are buffering the overall population decline. These findings suggest concrete conservation actions to halt the species' decline in the island. Installing thermally insulated nestboxes can mitigate the loss of lowland breeding sites and reinforce the highland population.