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Lead is highly toxic for wildlife, with pernicious consequences especially in long-lived predators. The causes of lead ammunition ingestion in Bonelli's eagle ( Aquila fasciata ) and its effects on breeding success were studied in one of the most important populations of this endangered species in Europe. Regurgitated pellets belonging to different pairs from 2004 to 2014 were analyzed, both in the breeding (1363 pellets from 12 territories) and non-breeding (172 pellets from 9 territories) seasons. From these territories, 57 molted feathers to study lead contamination were analyzed, and breeding success was monitored for 41 breeding attempts. The occurrence of lead shots in pellets was detected using X-ray photographs. Pellets were also used to describe eagle diet. Lead shots in pellets were present in 83.3% of the territories. The frequency of occurrence of lead shots in pellets (2.81% in spring and 1.31% in autumn) was primarily related to the consumption of red-legged partridge in the breeding season (when partridges are hunted from blinds using calling lures), and secondarily to rabbit consumption in the non-breeding season (coinciding with the main hunting season). Thus, our results indicate that injured small-game were the main source of lead contamination in the Bonelli's eagle. For the first time for a raptor species, a positive relationship between the frequency of occurrence of lead shots in pellets and lead concentration in eagles' feathers has been documented. Lead concentration in feathers (mean ± SD: 816 ± 426 μg kg − 1 , with no sex-related differences) was high for a species that rarely eats carrion or aquatic birds (the main prey-related lead source for raptors). This had negative effects on breeding success, which could jeopardize Bonelli's eagles in other European populations that are sustained by juvenile dispersal from the study population. Our work shows that some game modalities pose a potential threat to endangered raptors. [ABSTRACT FROM AUTHOR]

Background: Predation may potentially lead to negative effects on both prey (directly via predators) and predators (indirectly via human persecution). Predation pressure studies are, therefore, of major interest in the fields of theoretical knowledge and conservation of prey or predator species, with wide ramifications and profound implications in humanwildlife conflicts. However, detailed works on this issue in highly valuable -in conservation terms- Mediterranean ecosystems are virtually absent. This paper explores the predator-hunting conflict by examining a paradigmatic, Mediterranean-wide (endangered) predator-two prey (small game) system. Methodology/Principal Findings: We estimated the predation impact ('kill rate' and 'predation rate', i.e., number of prey and proportion of the prey population eaten, respectively) of Bonelli's eagle Aquila fasciata on rabbit Oryctolagus cuniculus and red-legged partridge Alectoris rufa populations in two seasons (the eagle's breeding and non-breeding periods, 100 days each) in SE Spain. The mean estimated kill rate by the seven eagle reproductive units in the study area was c. 304 rabbits and c. 262 partridges in the breeding season, and c. 237 rabbits and c. 121 partridges in the non-breeding period. This resulted in very low predation rates (range: 0.3-2.5%) for both prey and seasons Methodology/Principal Findings: We estimated the predation impact ('kill rate' and 'predation rate', i.e., number of prey and proportion of the prey population eaten, respectively) of Bonelli's eagle Aquila fasciata on rabbit Oryctolagus cuniculus and red-legged partridge Alectoris rufa populations in two seasons (the eagle's breeding and non-breeding periods, 100 days each) in SE Spain. The mean estimated kill rate by the seven eagle reproductive units in the study area was c. 304 rabbits and c. 262 partridges in the breeding season, and c. 237 rabbits and c. 121 partridges in the non-breeding period. This resulted in very low predation rates (range: 0.3-2.5%) for both prey and seasons [ABSTRACT FROM AUTHOR]

Density-dependent breeding performance due to habitat heterogeneity has been shown to regulate populations of territorial species, since the progressive occupation of low quality territories as breeding density increases may cause a decline in the mean per capita fecundity of a population while variation in fecundity increases. Although the preemptive use of sites may relegate low quality individuals to sites of progressively lower suitability, few studies on density dependence have tried to separate the effects of territory quality from individual quality, and none have simultaneously considered the effects of heterospecific competitors. Using two long-term monitored populations, we assessed the relative contribution of habitat heterogeneity and bird quality (in terms of age) on the productivity of sympatric golden Aquila chrysaetos and Bonelli's eagles Hieraaetus fasciatus under different scenarios of intra- and inter-specific competition. Productivity (number of offspring fledged) varied among territories and average annual productivity was negatively related to its variability in both species and populations, thus giving some support to the habitat heterogeneity hypothesis. However, the effect of habitat heterogeneity on productivity became non-significant when parental age and local density estimators were included in multivariate analyses. Therefore, temporal changes in bird quality (age) combined with intra- and interspecific competition explained variability in territory productivity rather than habitat heterogeneity among territories per se. The recruitment of subadult breeders, a surrogate of mortality in eagles, strongly varied among territories. Habitat heterogeneity in productivity may thus arise not because sites differ in suitability for reproduction but because of differences in factors affecting survival. Territories associated with high mortality risks have a higher probability of being occupied by young birds, whose lower quality, interacting with the density competitors, leads to a reduction of productivity. Site-dependent variability in adult survival and interspecific competition may be extensive, but so far largely overlooked, factors to be seriously considered for the site-dependent population regulation framework. [ABSTRACT FROM AUTHOR]

Abstract: Monitoring of the age of mates, a method proposed to detect early warning signals for demographic trends in long-lived bird populations, showed different patterns when the study was performed on a single Bonelli’s eagle subpopulation of Andalusia (South of Spain) than when the whole region is taken into account. In this respect, we discuss the role of the spatial scale, the origin of reduction in non-natural mortality and the definition of the used age classes. For a correct monitoring of the age of mates in the Bonelli’s eagle, we propose the two age classes previously suggested, adult and non-adult, but paying particular attention to the late subadult individuals, specially when the monitoring is performed in a wide region by different field work groups. Likewise, it is necessary for monitoring age of breeders in long-lived species with deferred maturity to collect data from a sample well distributed over space, taking regularly into account pairs from the edge and from the centre of population. Besides, it is important to monitor those subpopulations with different known threats, providing them their relative importance among the whole population. Finally, conventional monitoring of the age of mates seems to generally be a reliable way to predict viability changes of bird populations, except when adult by adult replacements take place by reduction in juvenile mortality. [Copyright &y& Elsevier]

We analyse the factors influencing breeding success in a healthy population of Bonelli’s eagle (Hieraaetus fasciatus) from south–east Spain, a raptor that has suffered a serious decline in Europe. Between 18 and 33 pairs were annually monitored during the period 1994–2002. Several factors that may affect four breeding parameters were studied, namely human presence, vegetation, relief, climatic factors, intra- and inter-specific relationships, diet, prey abundance, nest building, adult mortality and age of reproduction. A consistently high breeding success was registered during the study period (productivity=1.43, SD=0.11), which was probably the result of high adult survival, adequate prey availability and mild weather conditions. However, a certain vulnerability to the presence of golden eagles (Aquila chrysaetos) and to human disturbance was observed. One interesting result was the reduced survival of young chicks on north-facing cliffs owing to colder conditions, which may partially explain the decline of the Bonelli’s eagle populations along its European distribution limits. We discuss the role of this healthy subpopulation in an Iberian metapopulation context, and propose that the potential interference of golden eagles should be taken into account when designing management strategies for Bonelli’s eagles. Finally, we pinpoint some conservation priorities and the importance of reducing the main causes of adult mortality (i.e. shooting and electrocution) to assure successful reproduction and survival of this species. [Copyright &y& Elsevier]