Diego Ontiveros

Influence of prey densities in the distribution and breeding success of Bonelli's eagle (Hieraaetus fasciatus) : Management implications

Diet, prey availability, and breeding success were studied in a population of Bonellis eagle (Hieraaetus fasciatus) in the province of Granada, SE Spain. The densities of the main prey species, European wild rabbit (Oryctolagus cuniculus), red-legged partridge (Alectoris rufa), wood pigeon (Columba palumbus), and rock dove (Columba livia), representing 90.2% of the biomass, were analysed in 19 territories occupied by pairs of Bonellis eagles and 15 potential territories that were unoccupied but appropriate for nesting. We found no significant differences in prey density between the two types of territories. Contrary to other raptor species, we found no significant relationship between the density of their main prey species and the distance of the neighbouring pairs, either between that density and breeding success. These findings, together with the prior knowledge of nest-site selection of this eagle in the study area, can be used for proper planning of conservation strategies. These should avoid unnecessary effort to increase the eagles food supply, and should promote the reintroduction of individuals to suitable sites for Bonellis eagle.

Possible functions of alternative nests in raptors: the case of Bonelli’s Eagle

Four non-exclusive hypotheses have been proposed to explain the alternative nest-building behaviour of raptors: (1) nests as an advertising signal in territories, (2) frustration nests, (3) competition avoidance by nest-site and (4) reduction of nest ectoparasites. We report here data collected during an observational study of a population of Bonelli’s Eagle Hieraaetus fasciatus in southeastern Spain. Our data does not support the first two hypotheses based on the closeness of nests within territories, the lack of correlation between the number of nests and the distance to neighbours and the construction of secondary nests at similar frequencies after breeding failures as after successes. In contrast, the construction of alternative nests to avoid competition with other cliff-nesting raptor species breeding nearby was clearly important since 30% of the pairs obtained some direct benefit from the existence of alternative nests within their territories. We also found abundant Coleoptera (Dermestidae) and Diptera (Carnidae, Calliphoridae and Phoridae) as ectoparasites in nests, and the alternative use of nests, synergetically with the presence of greenery as mechanisms for avoiding ectoparasites, was an important factor for the breeding success of the eagle. Our data suggest that competition avoidance and, in particular, the reduction of nest ectoparasite hypotheses are the more plausible explanations for the maintenance of alternative nests in raptors.

Physical, environmental and human factors influencing productivity in Bonelli's eagle Hieraaetus fasciatus in Granada (SE Spain)

We analysed the productivity of the Bonellis eagle Hieraaetus fasciatus in relation to 26 variables that account for physiography, level of human presence, land-use, climate, laying date, and nest orientation, in the province of Granada (SE Spain), where a stable population exhibits the maximum productivity value for the species in Europe. Productivity positively correlated with cliff availability within territories and closeness of nest site to SE orientation. Cliff availability permitted some pairs to choose the best nest site orientation, thereby favouring high productivity. Nests in the preferred orientation (SE) had 35% higher productivity than those towards non-preferred orientations. Higher productivity in the best orientation nests might be related to warmer conditions. High productivity in the study area could offset the main problem for Bonellis eagle conservation in Europe, that is, the high preadult and adult mortality. Actions required to ensure the recovery of neighbouring populations must focus on the preservation of high cliff availability and the diminution of preadult mortality in southeastern Spain. This would favour restocking of the decreased northern populations by the juvenile dispersion.

Habitat features of settlement areas used by floaters of Bonelli's and Golden Eagles

Summary Bonelli’s Eagle Hieraaetus fasciatus and Golden Eagle Aquila chrysaetos are two declining species, in which floaters tend to be located outside of breeding territories during the dispersal period, in so-called settlement areas. We studied settlement areas for both these long-lived raptors in the southern Iberian Peninsula, to gain a better understanding of the ecological requirements of the eagles during their long pre-adult stage, a period accounting for around 80% of the species’ mortality. Eagle abundance was calculated by road censuses, and habitat characteristics of settlement and non-settlement areas compared by General Discriminant Analysis (GDA) and Logistic Regression (LR). The best model of GDA and LR incorporated the abundance of main prey for eagles (rabbits, partridges) and orchard surface area, and explained 100% of eagle presence; the best model selected by GDA also included habitat heterogeneity. Both eagles tended to share settlement areas in the southern Iberian Peninsula and, when they did not, the mean annual temperature and slope appeared to explain the segregation between the two species. Management measures for the conservation of both threatened species during the dispersal period should be focused on identifying settlement areas, maintaining high prey densities and maximum habitat heterogeneity.

The Coexistence of the Eagles Aquila chrysaetos and Hieraaetus fasciatus Increases with Low Human Population Density, Intermediate Temperature, and High Prey Diversity

Competition among species with similar ecological requirements may preclude species coexistence. However, species with similar requirements may coexist under determinate environmental conditions. Major effort is being dedicated to conserve the golden eagle (Aquila chrysaetos) and Bonellis eagle (Hieraaetus fasciatus) in Spain, two raptors with similar ecological requirements. This work analyses how some key ecological factors correlate with the coexistence of the two eagles, which may help to optimize the conservation plannings of the two species. Findings show that low human population density favours eagle coexistence, because human presence is harmful for both eagles. Temperature is an important factor affecting the segregation of the two eagles, with Bonellis eagle dwelling in warmer zones than the golden eagle, but overlapping in squares with intermediate temperature. High prey diversity facilitates the coexistence of the two eagles, possibly because it encourages trophic segregation. Conservation planning for both species would be enhanced by the protection of zones with low human population density, intermediate temperature, and high prey diversity, which seem to favour the coexistence of the two eagles.

The feeding ecology of Bonelli’s eagle (Aquila fasciata) floaters in southern Spain: implications for conservation

Although many studies have investigated the feeding habits of Palaearctic raptors, few have analysed non-breeding populations during dispersal. Bonelli’s eagle (Aquila fasciata), a threatened species in Western Europe, has a relatively long and critical dispersal period. We studied feeding habits, prey selection, and the influence of prey density on floater abundance in this species during its dispersal period in southern Spain. Differences were found between the diet of floaters and that of the closest breeding populations. Diet diversity was rather low for floaters, with European wild rabbits (Oryctolagus cuniculus) being the main prey and the only prey positively selected. Moreover, the number of floater Bonelli’s eagles observed in the dispersal areas was positively associated with rabbit abundance. Other prey included red-legged partridges (Alectoris rufa) and pigeons (Columba sp.). We propose measures to match suitable prey availability for floater eagles in settlement areas and the use of such areas as human hunting fields.

FEEDING HABITS OF THE COMMON CHAMELEON, CHAMAELEO CHAMAELEON (LINNAEUS, 1758) IN THE SOUTHEASTERN IBERIAN PENINSULA

ABSTRACT We present the feeding habits of the common chameleon (Chamaeleo chamaeleon) at Taramay, a small coastal valley in the southeastern Iberian Peninsula. Fecal pellets collected from sexed and measured specimens trapped in the field were used for diet analysis. Thirty-four fecal samples provided a total of 777 identified prey items. All prey were arthropods and the numerically dominant groups were Diptera, Hymenoptera, Orthoptera, and Heteroptera. We failed to find sexual differences in diet preference, but there was a seasonal shift in the prey consumed. Orthoptera, the largest prey type, was consumed less in spring than summer or autumn. Examination of grasshopper phenology in coastal habitats of the southeastern Iberian Peninsula, and of the change in chameleon habitat utilization and mobility during the mating period, verified that the common chameleon appears to consume grasshoppers in approximate proportion to their abundance. Prey consumed were smaller than in previous studies. We believe the...