Nest-site overlap and coexistence between Bonelli’s Eagle (Hiera tus fasciatus) and Peregrine Falcon (Falco peregrinus) in an area of simpatry.

Nest-site selection has been compared between the populations of Bonellis Eagle (29 pairs) and Peregrine Falcon (35 pairs) in an area of simpatry in Southeastern Spain (Granada province). 18 variables evaluating habitat humanisation, physiography, intraspecific and interspecific distances and vegetation (Appendix 1) were compared between both species (t-test). These variables were used to make a habitat selection model for each one by comparing occupied cliffs with non-occupied cliffs (t-test) and by means of discriminant functions (Forward Stepwise Discriminant analysis). Only three variables were significantly different between peregrines and eagles, the distances to Eagle nests, the distances to Falcon nests and the forest cover (Table 1). Intraspecific distances were greater than interspecific distances, because both species had a tendency to nest close together in areas with a high cliff availability. However, nest-site selection models were quite different, because the Peregrine Falcon tolerated human presence better than the Bonelli’s Eagle. The Peregrine Falcon model showed six variables different from non-occupied sites, and only one of them (number of km of roads around the nest) was related to human presence, while the Bonellis’ Eagle model showed nine variables different from non-occupied sites, four of them directly related to human presence (distance to the nearest village, distance to the nearest road, number of km of roads around the nest and number of km of trails around the nest) and one indirectly related to human presence (topographical irregularity). The discriminant functions selected as variables included in the model the number of kilometres around the nest and the interespecific distance for the Peregrine Falcon (79.9% of correct classification), and for the Bonelli’s Eagle, the topographical irregularity and the distance to the nearest village (80% of correct classification). The nest-site selection divergence and the high cliff availability may decrease the interespecific competition. However, Bonelli’s Eagles excluded Peregrines Falcons from isolated cliffs that were adequate for Peregrine Falcons (n = 8). This fact indicates that the Bonelli’s Eagle is the dominant species.

Gil Sanchez, J. M, Ardeola 46(1), 1999, 31-37