Vegetation, precipitation and demographic response of a woodland predator: Tawny Owl Strix aluco as an indicator of soil aridity in Castelporziano forest

Abstract

The demographic performance of avian predators is influenced by climate variations. The Plant Area Index (PAI) is considered a key descriptor of the (evolving) vegetation sensitive to climate and soil aridity and drought stress. To assess if the increased aridity regime in the mediterranean region affects the reproduction of a forest predator, the breeding success of the Tawny Owl Strix aluco was studied over 7 years (1997–2003) in Castelporziano, central Italy. The inter-annual fluctuations in owl demographic output observed in neighbor forest and agricultural sites were compared with climatic variables (rainfall, minimum and maximum air temperature, aridity index) and changes in the PAI estimated by satellite imagery. Out of 326 breeding attempts, the percentage of successful pairs per year ranged between 4 and 28 %, the number of fledglings per successful pair ranged between 1.0 and 1.8 and breeding rate (i.e. the number of fledglings per breeding pair) ranged between 0.1 and 0.4. Demographic, climatic and remotely sensed indexes showed coherent variations among years. Rainfall and lower aridity index are associated with a higher breeding success. The relationship between PAI and breeding rate was found significant only in forest sites. Results suggest that Tawny Owls may positively respond to drier weather conditions by reducing the breeding rate.