Habitat preferences and causes of population decline for Barn Owls Tyto alba: A multi-scale approach

Aims: Habitat preferences of Barn Owls was studied in two areas of Spain undergoing large-scale habitat alteration. Location: Alicante (dry cultivations) and Valencia (irrigated cultivations) in eastern Spain. Methods: Habitat composition around occupied and unoccupied territories in dry cultures and irrigated cultures was compared (n = 71, 1989-2000). This study also described differences in habitat composition between occupied and deserted territories after major habitat alterations started in 1996. Generalized Linear Models were used to examine patterns of habitat preference at three different spatial scales: nest site, home range and landscape. Results: The study population declined by 69% in both study areas. At the nest site scale, Barn Owls preferred undisturbed areas with high availability of cavities, mainly in man-made structures. At the home range and landscape scales, Barn Owls occupied undisturbed areas with a high availability of cavities and high percentages of edges and ditches. Territory desertion was prompted by the modernisation or disappearance of man-made structures, depletion of edges and ditches, expansion of the road network and persecution. Accordingly, the spatial distribution of territories in irrigated cultures changed from uniform to random after habitat alteration. The availability of cavities alone does not account for all of the explained deviance, i.e., Barn Owls occupy structurally complex landscapes. Conclusions: Compensation measures for habitat loss such as nest-box programs, usually proposed within the framework of environmental impact assessment, are discouraged unless habitat restoration and effective control of persecution are promoted first.