Prey selection by Bonelli´s eagles (Hieraaetus fasciatus) during the breeding season in Granada (Southeastern Spain).

Published:

Volume 45(2), December 1998. Pages 151-160.

Language:

Spanish

Original title:

Selección de presa por el Aguila-Azor Perdicera (Hieraaetus fasciatus) durante el periodo de nidificación en la provincia de Granada (SE de España).

Keywords:

Alectoris rufa, diet, Hieraaetus fasciatus, Oryctolagus cuniculus, prey selection.

Abstract:

Prey selection by five pairs of Bonelli´s Eagles was studied during the breeding season in the Granada province, southeastern Spain, a typical Mediterranean area. The abundance of birds, squirrels and lizards was estimated by means of 1-3 line transects covering 3.5-9.5 km carried out within the territory of each eagle pair (Table 1). Rabbit abundance was estimated from counts of droppings carried out within 2-m wide bands along each transect. Rabbit density (No. individuals/ha) was then computed from dropping counts by means of a conversion factor developed from simultaneous counts of both droppings and rabbits carried out in one of the studied territories. Diet was characterised by means of pellet analyses (n=51). Eleven prey categories were considered: rabbits, hares, squirrels, water voles Arvicola sapidus, Red-legged Partridge Alectoris rufa, pigeons, corvids, large birds, medium-sized birds, small birds and ocellated lizards Lacerta lepida. Prey selection was analysed by means of the Savage´s index (Wi). The diet (n=238 prey) was based on rabbits (39.9%) and, secondarily, on Red-legged Partridges (24.7%). Pigeons, ocellated lizards, corvids and other birds appeared in low proportions. Rabbits were positively selected by one out of the five pairs (Wi=1.63, P<0.01/2k; k=number of prey categories) and negatively selected by another one (Wi=0.40, P<0.005/2k). Red-legged Partridges were positively selected by one pair (Wi=1.98, P<0.005/2k) and pigeons were negatively selected by three pairs (Wi=0.43, P<0.05/2k; Wi=0.15, P<0.005/2k; Wi=0,15, P<0,005/2k). Small birds were constistently avoided by all pairs, whereas the remaining prey types were apparently captured on the basis of their availability. Bonelli´s Eagles behaved as generalist predators except in the case of small birds, also showing a slight tendency to prefer Red-legged Partridges over other available prey. Rabbits and Red-legged Partridges seem to be the most profitable prey available in Mediterranean areas for Bonelli´s Eagles, so that the low electivity of rabbits found was hardly expected. Daily patterns of habitat use by rabbits and the structure of the vegetation within eagle territories are discussed as likely causes for the differences in rabbit selectivity showed by the five studied pairs.