Territorial birds of prey adjust their flight behaviour over the course of the breeding season depending on their breeding success

Movement is a key behaviour to better understand how individuals respond to their environment. Movement behaviours are affected by both extrinsic factors that individuals face, such as weather conditions, and intrinsic factors, such as sex and experience. Because of the energy costs it entails, movement behaviours can have direct consequences on an individual's demographic parameters-and ultimately on population dynamics. However, the relationship between extrinsic factors, intrinsic factors, daily movement behaviour and demographic parameters such as breeding performance is poorly known, in particular for central place forager territorial species. We investigated here the link between movement behaviours and breeding performance of the French population of Bonelli's eagle (Aquila fasciata), a territorial and sedentary long-lived raptor, and how this link may depend on extrinsic and intrinsic factors. By using data from annual monitoring of breeding performance for the population and GPS tracking of 48 individuals (26 males and 22 females), we found that the breeding performance of this population was mainly driven by whether a new individual was recruited into the territory, and only slightly by weather conditions. Movement behaviours (proportion of time in flight, range of movement and straightness of trajectories) showed large between-individual variation. Those behaviours were related with weather conditions (wind and rainfall) at a daily scale, as well as with individual's experience. We found only one significant correlation between movements and breeding performance: male Bonelli's eagles spending more time flying during chick-rearing phase had lower productivity. Movement behaviours and breeding performance were also indirectly linked through individual's experience, with more experienced birds having better breeding success and a shorter range of movement and spent less time in flight. This suggests that experienced individuals progressively acquire knowledge of their breeding territory, are more efficient in finding prey, and adapt their foraging strategies to weather conditions to minimise energy costs, allowing them higher breeding performance.

GPS tracking has enabled significant advances in the study of animal movements such as migration and habitat use. However, GPS devices can affect the behaviour of tagged individuals, especially for flying animals such as birds, and may ultimately impair their reproduction and/or survival. While numerous studies have investigated the potential negative effects of GPS‐tags on birds, few have simultaneously looked at these effects on reproduction and survival, with studies on the latter sometimes suffering from methodological flaws. This study investigated the effects of GPS‐tagging on the breeding success and survival of a medium‐sized raptor, Bonelli's Eagle Aquila fasciata. Forty‐five breeding adults were equipped with backpack‐mounted GPS‐tags representing 1.2–3.5% of individual body mass. Using a recently developed capture–mark–recapture model that accounts for differences in detectability between types of tags (metal ring, coloured ring or GPS), our results showed no significant differences in survival or breeding success between GPS‐tagged and banded individuals. Overall, we did not observe deleterious effects of GPS‐tagging on Bonelli's Eagle that would warn against the use of GPS‐tags in this species, or other medium‐to‐large raptors, given the relevant information they might provide for conservation.

From sport hunting to breeding success: Patterns of lead ammunition ingestion and its effects on an endangered raptor

Survival is a life history trait that contributes most to population dynamics in long‐lived birds, and the study of individual characteristics is relevant for population conservation. Here we provide information on territorial recruitment and individual replacement in a population of Bonelli's eagle Aquila fasciata in southeastern Spain based on a long‐term photographic capture–recapture 19‐year dataset. We also investigated how individual factors such as sex, age, experience and age at first breeding influence the apparent survival of breeding Bonelli's eagles using Cormack–Jolly–Seber models. An increase in recruitment rates and a decrease in age at first breeding were observed in the breeding population over time. The apparent survival was high and the reproductive dispersal was very low. The improvement in apparent survival was age‐related and higher in females (0.90 for non‐adults and 0.92 for adults) than males (0.87 for non‐adults and 0.89 for adults). These findings can be explained by age‐related improvements and differences in movement behaviour between sexes during the breeding season, with females being exposed to lower risks from anthropogenic or natural causes. We also found a positive relationship between territorial experience and the probability of apparent survival, with inexperienced female breeding birds having a higher survival than males. Our results showed that immature breeders had a similar survival to experienced or older birds breeding for the first time, suggesting that age at first reproduction is controlled by reproductive restraint. Our results provide demographic information that improves the understanding of the population dynamics of the long‐lived territorial species, and their estimation has important implications for the management and conservation of Bonelli's eagle populations.

BackgroundPredation 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 human-wildlife 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 FindingsWe 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.Conclusions/SignificanceThe potential role of Bonelli's eagles as a limiting factor for rabbits and partridges at the population scale was very poor. The conflict between game profitability and conservation interest of either prey or predators is apparently very localised, and eagles, quarry species and game interests seem compatible in most of the study area. Currently, both the persecution and negative perception of Bonelli's eagle (the ‘partridge-eating eagle’ in Spanish) have a null theoretical basis in most of this area.

Identifying the priority habitats of endangered species is crucial to implementing effective conservation actions. We characterize the key habitats used by Bonelli's Eagle Aquila fasciata, an umbrella and flagship species that is endangered in Mediterranean countries. We radiotracked 17 breeding individuals (10 males and seven females) in Catalonia (NE Iberian Peninsula) and used compositional analysis to determine the key habitats in home‐ranges of both sexes. The main habitats identified within the home‐range area were scrubland, coniferous forests, cropland, sclerophyllous forests, rock outcrops and urban areas, with little difference in habitat use between the sexes. Bonelli's Eagles preferred rocky habitats as breeding areas and scrubland as foraging areas, as these hold the highest abundance of their main prey, Rabbits Oryctolagus cuniculus and Red‐legged Partridges Alectoris rufa. Habitat selection varied seasonally in foraging areas: scrubland was the most preferred habitat type during the breeding season, whereas rocky areas were preferred during the non‐breeding season (although scrubland was also highly selected). Urban areas were avoided both as breeding and as foraging areas. Home‐range size was inversely correlated with the proportion of scrubland, suggesting that this is a key habitat for Bonelli's Eagle. To conserve this species effectively, policies that ensure the preservation of the cliffs used as breeding sites, as well as suitable management of the scrubland used for foraging, should be implemented in the areas inhabited by this species. The promotion of traditional land uses and management techniques that will enhance open areas in Mediterranean landscapes should in the future play an essential role in the conservation of Bonelli's Eagle in Mediterranean habitats.

Linking density, productivity and trends of an endangered species: The Bonelli's eagle in Spain

There has been increasing recognition of the adverse effects of outdoor recreation on the behavioural ecology, breeding success and ultimate abandonment of territories in several raptor species, such as the Bonelli's Eagle (Aquila fasciata). We assessed the effects of human activities on the behaviour and breeding success of Bonelli's eagles breeding in south‐eastern Spain, using a 14‐year long‐term data set. Our results showed a weak behavioural response to human activities. The probability of eagle reaction varied among the human activities assessed and increased when they occurred close to a nest, being most marked for ecotourism activities. In general, the probability of a bird reacting increased sharply when an activity occurred closer than 480 m from the nest, but reactions were negligible when an activity occurred 1000 m away. Ecotourists only affected Bonelli's eagle behaviour at distances <300 m from the nest. We found a negative relationship between human activity and Bonelli's eagle behaviour: the probability of a reaction decreased with the increasing frequency of human activities, suggesting a degree of eagle habituation. Breeding success did not vary with a pair's experience of disturbance, nor between the periods before, during and after the COVID‐19 lockdown but did increase with the frequency of human activities. Our results indicated that Bonelli's eagles can develop a degree of tolerance to human activities during the nesting season. This behavioural plasticity offers the opportunity to harmonize anthropogenic activities with the application of specific conservation measures for this species in humanized landscapes. Our findings led to suggestions to minimize the detrimental effects of human activities and to optimize the conservation management of Bonelli's eagles in Southeastern Spain. More generally, our study emphasises the value of behavioural ecology studies for guiding conservation. Read the free Plain Language Summary for this article on the Journal blog.

Trichomonas gallinae is a pathogen of conservation relevance, whose main maintenance hosts are Columbiformes, but spillover to avian predators has been described. The goal of this study was to characterize the epidemiology of Trichomonas spp. in a community of free-ranging domestic and wild Columbiformes and an endangered predator, Bonelli's eagle Aquila fasciata. We surveyed 253 live-captured Rock doves, 16 nestling Bonelli's eagles and 41 hunted Columbiformes. Oro-esophageal swabs were incubated in culture media and Trichomonas spp. isolated from Bonelli's eagle (6.3%, CI95 1.1-28.3), Turtle dove Streptopelia turtur (56.3%, CI95 39.3–71.8), Wood pigeon Columba palumbus (83.3%, CI95 43.7–97.0) and Rock dove Columba livia (68.4%, CI95 62.4–73.8). Infected Rock doves showed significantly poorer body condition than uninfected ones (p = 0.022). From a subset of 32 isolates, 18S and ITS1/5.8S/ITS2 rRNA genes were sequenced and Maximum-Likelihood trees inferred. Four ribotypes of Trichomonas spp. were identified. In this study area Trichomonas spp. seem to persist in a multi-host system involving several species of Columbiformes. Conservation actions aimed at increasing the availability of trophic resources for Bonelli's eagles through Rock dove restocking should consider the risk of pathogen transmission and of introduction of alien strains.

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

Aim To assess the impact of certain climatic variables on the breeding success of some populations of Bonelli's eagle (Hieraaetus fasciatus V. 1822) throughout its latitudinal distribution range, in order to account for recent and differential declines in populations.Location Western Mediterranean, from southern Morocco to southern France.Methods Seven populations were considered for the latitudinal distribution range of the species. Data from 1052 breeding attempts were taken from the literature and, for each population, breeding success was measured as the mean number of fledglings per pair per year. Breeding success, as a dependent variable, was related to five geographical and climatic variables (latitude, mean annual temperature, mean minimum temperature of the coldest month, mean maximum temperature of the hottest month and mean annual precipitation) as independent variables, through some regression models, which take into account the multicolinearity of the variables.Results All the analyses agreed that average annual temperature was an important factor associated with the breeding success of the species in each region, and accounted for up to 97% of the variance of the breeding success throughout a latitudinal gradient in the study area.Main conclusions The low breeding success of the northern populations (probably because of climatic constraints) and the tendency of juveniles to disperse southwards, diminishes recruitment in those populations. Therefore, as human pressure and habitat destruction causes high adult and pre‐adult mortality of the species throughout its entire latitudinal range, disturbances in the northern populations have more profound effects, thereby explaining observed population declines.

Mate desertion by male Great Reed Warblers <i>Acrocephalus arundinaceus</i> at the end of the breeding season

Illegal trade in wildlife has been identified as one of the main challenges to wildlife conservation. In 2010, an illegal trade‐ring trafficking in birds of prey was uncovered in Sicily (southern Italy). This illegal trade targeted the three most endangered species in Italy: Bonelli's eagle Aquila fasciata, Lanner falcon Falco biarmicus and Egyptian vulture Neophron percnopterus, all of them long‐lived territorial raptors threatened with extinction across their European distribution. Illegal harvest primarily involved young birds and eggs taken from nests. After the discovery of these activities, surveillance camps and camera traps connected to the mobile Global System for Mobile communications network were established in nine Bonelli's eagle breeding sites in which illegal harvest was reported. Surveillance activities resulted in a sharp reduction in illegal harvest that has contributed to the recent increase in population size and number of breeding pairs of Bonelli's eagle in the island. This population represents 95% of the entire Italian population and is catalogued as Critically Endangered in this country. Importantly, our results highlight the impact of illegal harvest on the population dynamics of endangered species as demonstrated by a population viability analysis. This is particularly important in the case of insular species for which demographic recovery due to immigration from other geographic areas is unlikely. Systematic patrols by forestry police authorities, a resolute application of Convention on International Trade in Endangered Species legislation via legal punishment, and the requirement of including all live captive specimens used for falconry in an obligatory DNA data bank would contribute to reducing the risk of extinction for small populations of endangered species of birds of prey.

Understanding the selective pressures shaping the number of offspring per breeding event is a key area in the study of life-history strategies. However, in species with parental care, costs incurred in offspring production, rather than rearing, have been largely ignored in both theoretical and empirical studies until relatively recently. Furthermore, the few experimental studies that have manipulated production costs have not yet teased apart effects that operate via the parental phenotype from effects on the quality of the resulting young. To examine whether increased egg production influences parental brood rearing capacity independently of effects operating via egg quality, we experimentally increased egg production in gulls and then examined their capacity to rear a control clutch. We found that the capacity of parents to rear the control brood was substantially reduced solely as a consequence of having themselves produced one extra egg. The paradox that, in many species, parents apparently aim for fewer young per breeding event than the experimentally and theoretically demonstrated optimum, has partly arisen from the failure to take into account the constraints imposed by production costs.

Summary Predator conservation management requires detailed understanding of the ecological circumstances associated with predation, especially that on economically valuable prey. We examined the mechanisms behind Bonelli's eagle Hieraaetus fasciatus predation on prey of domestic origin, using dietary data from 22 pairs breeding in south‐west Portugal (1992–2001) together with information on landscape composition and prey availability. Numerically, 42·7% (37·7% in biomass) of eagle prey comprised domestic species, about 70% of which were rural pigeons Columba livia and the remainder were racing pigeons Columba livia and domestic fowl Gallus gallus. Rabbits Oryctolagus cuniculus, red‐legged partridges Alectoris rufa and jays Garrulus glandarius were the most frequent wild prey (43·1%; 50·8% in biomass). This dietary pattern was remarkably stable over a decade, but within each year the intake of pigeons almost halved over the course of the breeding season. Landscape composition significantly affected the dietary proportion of wild and domestic prey items. This was particularly evident in territories dominated by eucalyptus Eucalyptus globulus plantations, where there was reduced consumption of rural pigeons and partridges, an increased intake of minor avian prey items and greater diversity in the diet overall. Bonelli's eagles showed type II functional responses while preying on the most important wild (rabbit) and domestic (rural pigeon) prey, although the former was much stronger. Eagle predation on rabbits declined with increasing abundance of pigeons, and vice versa, but there was no switching in the traditional sense, as selection between these two species was inversely frequency dependent. Synthesis and applications. Predation by Bonelli's eagle on domestic pigeons results from a combination of high vulnerability of the pigeons to eagles and a shortage of key wild prey such as rabbits and partridges, especially during the early breeding season. Given the relatively low economic value of rural pigeons and their importance in the diet of Bonelli's eagles, they could probably be used as a conservation tool to enhance food resources in breeding territories and to deflect predation from more valuable prey such as partridges and racing pigeons.