The effect of intra- and interspecific interactions on the large-scale distribution of cliff-nesting raptors

We examine the large-scale spatial distribution and the intra- and interspecific interactions in a cliff-nesting raptor community of a semi-arid Mediterranean area in southeastern Spain. The study community was composed of four top avian cliff-nesting predators: the Golden Eagle Aquila chrysaetos, the Bonelli's Eagle Hieraaetus fasciatus, the Eagle Owl Bubo bubo and the Peregrine Falco peregrinus. We tested the null hypothesis that their nest sites were distributed randomly within the study area, and built regression models as a function of the nearest neighbour distances (NNDs) among them. During a 15-year research period, we found a total of 560 traditional nest sites. Only those of A. chrysaetos showed regular spacing over the study area, while the distributions of the other three species did not differ significantly from random. Our modelling approach demonstrated that intraspecific NNDs were important only for the two largest species, A. chrysaetos and H. fasciatus, suggesting intraspecific territorial spacing for A. chrysaetos, but a certain degree of spatial aggregation for H.fasciatus. In addition, the models suggested competitive interactions between these species. According to the relative importance of their interspecific NNDs, H. fasciatus appeared to be dominant over the smaller F. peregrinus. Strong interspecific interactions were also suggested between B. bubo and F. peregrinus. Intra-and interspecific relationships within the community followed a general pattern of dominance related to body mass. Notable exceptions were found especially for the interspecific interactions involving B. bubo, which may prey upon the other species.