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Demography and diet of Bonelli's Eagle (Hieraaetus fasciatus) in Granada (SE Spain)

Abstract:

During 1994-1999 a monitoring program was developed on the population of Bonelli's Eagles breeding in Granada (southeastern Spain). Breeding territories were surveyed every year so that both the reproductive success and the survival of adults could be recorded. The diet during the breeding period was also studied by mean of the analysis of pellets collected near the nests. The population is composed of 39-45 pairs and the demographic evolution was positive during the study period, so that three new pairs have been established (mean annual increase: 1.66%). The reproductive success was high, with a mean number of fledglings per controlled pair of 1.49 and a mean number of fledglings per successful pair of 1.66 (n = 132 controlled reproductions). The breeding success was remarkably constant during the study period (Table 1). Minimum adult mortality was low, with a mean annual value of 2.33% (Table 1). The positive demographic evolution was related to both the high reproductive success and, specially, to the low adult mortality recorded. Diet was based on rabbits Oryctolagus cuniculus and Red-legged Partridges Alectoris rufa, with scarce local variation (n = 1339 prey; Table 2). Diet was also very constant throughout the study period (Friedman test: 2 = 1.82; d.f. = 4; P > 0.05; Fig. 2); however, a slight, albeit nonsignificant, decreasing trend for rabbits was detected during the last three years (Fig. 1). The high and constant reproductive success was probably related to an optimal and constant diet based on prey of high energetic value.