Towards accurate and simple morphometric sex differentiation in Bonelli’s Eagle Aquila fasciata nestlings: Interpopulation variations and influence of growth conditions

Morphometric methods of sex differentiation may be cheap, simple, quick, and reliable alternatives to molecular approaches. However, there are still important uncertainties regarding the use of morphometric methods in birds, particularly regarding their applicability to different populations and environmental conditions. Between 2004 and 2019, we sampled 245 Bonelli´s Eagle Aquila fasciata nestlings, 197 from nests in Catalonia (northeastern Spain) and Andalusia (southeastern Spain) and 56 that were partially or totally raised in captivity. Our objective was to develop morphometry-based sexing methods for Bonelli’s Eagle nestlings that can be applied in situ to different subpopulations and growth conditions. We recorded up to nine measures related to nestling body mass, bill, tarsus, and claw length. Tail and wing length were used to control for the age of nestlings, and all individuals were sexed genetically. We found important morphometric differences between the two natural subpopulations. According to our discriminant analyses, body mass and claw length were the most discriminant variables, both in wild and captivity conditions. Differences between sexes were more prominent during the flight feathers’ growing period. Feeding ad libitum in captivity conditions led to larger nestlings and reduced between-sexes differences. We provide different models for sexing Bonelli’s Eagle nestlings that can be applied according to the studied geographic location, growth conditions (wild versus captive), and balance between accuracy and simplicity. Overall, our findings highlight that extrapolating sex discriminant functions to different subpopulations and growth conditions may be risky.

Status and distribution of diurnal raptors in Central North Algeria, the case of Great Kabylia

In 2018 and 2019 thirteen species of raptors, with 407 individuals, were found nesting in Great Kabylia in Algeria. During this period, 196 raptor nest sites were located (Falco tinnunculus is not included as it thrives in many biotopes and tolerates anthropization). We noted a decrease in specific richness and abundance of raptors in the region compared to data for 1992. Some raptors were not seen during our study: Gypaetus barbatus, Pandion haliaetus, Falco biarmicus, Circaetus aeruginosus, and Falco eleonorae. We classified nesting diurnal raptors into 3 classes according to their relative abundance: (1) widespread species (10-26 %): F. tinnunculus, Hieraaetus pennatus, and Buteo rufinus cirtensis; (2) common species (5-10 %): Elanus caeruleus, Falco peregrinus, Circaetus gallicus, Falco naumanni, Gyps fulvus, and Milvus migrans; and (3) uncommon species (1-5 %): Neophron percnopterus, Accipiter nisus, Aquila fasciata, and Aquila chrysaeto. With the exception of N. percnopterus, which is classified as an endangered species, the raptors of Great Kabylia are mainly classified in the category of species of least concern (IUCN, 2020). Dataset published through GBIF (Doi: 10.15470/wt5dgi).

Nest-Building Effort is Not An Indicator of Male Quality In Bonelli’s Eagles, Aquila fasciata

Raptors often use a variety of materials to build their nests (natural, such as branches, but also non-natural objects), presumably due to their insulating properties, their suitability to advertise occupancy of the nest, and to decrease pathogen and parasite loads. The amount of branches used in a nest is an indicator of parental quality and is often associated with increased breeding success. However, in raptors where both sexes collaborate in nest construction, it is unclear whether the effort expended by males (taking the amount of material carried to the nest as the potential predictor) could constitute an honest signal of parental quality to female conspecifics. We examined data on sex, type of material brought to the nest, breeding experience, timing, and nest-building investment prior to egg-laying from 32 identifiable Bonelli’s Eagles (Aquila fasciata) during the pre-laying period to investigate the relative contribution of the sexes to the amount of nest material gathered. We asked: (1) whether the nest-building investment of males could provide information to the females about their quality; and (2) whether the amount of material delivered to the nest by the male was related to breeding success. Despite the considerable investment of males in nest-building during the pre-laying period, our results indicate that this effort is not a consistent indicator of male quality to the female. Therefore, male nest-building behaviour and investment by Bonelli’s Eagles cannot be considered as an extended expression of their phenotype (an extended phenotypic signal). Nest-building behaviour by males in the early and late stages of nest-building, and the fact that males were not significantly more active builders, are discussed in the contexts of signaling nest occupancy to conspecifics and competitors, the decrease of parasite loads, and the strengthening of the pair-bond during the pre-laying period.

Detection of Individual Replacements in a Long-Lived Bird Species, the Bonelli'S Eagle (Aquila fasciata), Using Three Noninvasive Methods

ABSTRACT Accurate estimations of adult mortality are essential for understanding population dynamics and achieving efficient management actions that are directed toward long-lived species. Several noninvasive methods may be used to monitor endangered long-lived birds like raptors, but their performance in real-world scenarios remains poorly studied. We used eight Bonelli's Eagle (Aquila fasciata) breeding pairs (1) to compare the efficiency of direct observations with binoculars and telescopes (2004–2016), camera trapping (2012–2016), and feather genetic analysis (2004–2015) for detecting and identifying individuals over time, (2) to conduct a cost-benefit analysis of methods, and (3) to evaluate the accuracy of the direct observation method for estimating survival by comparing it with camera trapping and feather analysis. Both the feather genetic analysis and camera trapping approaches allowed us to successfully identify individuals and to detect replacements that we did not notice during direct observations. The classic direct observation method overestimated adult survival, which could hamper an accurate understanding of the demographic dynamics of this population. Feather analysis gave a low detection rate of individuals (47%), probably due to difficulties in finding feathers in the rugged habitat of this species. However, identification success at the individual level with this method was 96%. Remote camera surveys had both a high detection rate (100%) and identification success (93%). Given that costs associated with camera surveys were lower than the costs of genetic procedures, we concluded that camera trapping is the most efficient indirect method to assess adult survival in this and other raptors with external features that make individual identification possible. However, because no method showed complete efficiency, genotyping of feathers collected at the end of the breeding season could be a useful additional method, especially when camera trapping is not possible or when it fails.

The Limit to the Density of Species (A Reflection on Human Intervention in Conservation and Its Effects)

Human actions on the natural environment cannot always be considered as impacts resulting from their behavior to survive. Many of these activities have caused irreversible damage and changes in the landscape, flora, and fauna. By contrast, several actions, carried out “a priori” with the best intention, to help in the conservation of species considered in danger, have caused a dangerous decompensation. Aid for the recovery of some species of birds has led to their overpopulation. The artificial contributions of food, always in the same places, have caused an excessive increase in the number of griffon vultures (Gyps fulvus), which has produced the reduction of other endangered species, such as the black stork (Ciconia nigra) and the Bonelli’s eagle (Aquila fasciata), which have been displaced from the rocks in which they nested due to the harassment of a greater number of vultures. Besides, vultures are attacking domestic livestock at the most defenseless times, such as during calving. Greater flamingo (Phoenicopterus roseus) has become out of control in numbers in Europe. The two classic breeding areas, La Camargue (France) and La Laguna de Fuente de Piedra (Spain) have produced an enormous annual number of individuals that are distributed among the few lagoons of Mediterranean Europe. The wetlands are devastated by the flamingo, which removes the mud and prevents sunlight from reaching the underwater vegetation, turning these lagoons into dead water, having to be abandoned (temporarily) by most aquatic species, including the flamingo. The shortage of food resources of natural origin, for such a disproportionate number, has caused the flamingo to invade the rice fields, accepting its grain as a substitute for the invertebrates that it habitually consumed, and which are now scarce. The same is the case with the white stork (Ciconia ciconia) in southern Europe. The increase in their population has reduced the number of reptiles and amphibians, bringing several of their species to the brink of extinction. Storks have varied their prey spectrum, consuming carrion, and preying on Montagu’s harrier (Circus pygargus) brood. In these cases, and many others, the theory of “the more the better” is not valid. If we want to make the protection of some species compatible with the conservation of others, it seems necessary to redirect some situations …

Guiding local-scale management to improve the conservation of endangered populations: the example of Bonelli’s Eagle Aquila fasciata

Summary Understanding the environmental drivers of demographic processes is a prerequisite for providing the evidence-based conservation guidance and management actions required to address management goals at population level. Human activities, to which most species are not adapted, are having an ever-increasing impact on the environment. Most policies and strategies focus on broad-scale conservation actions and disregard the fact that this type of action may not be adequate at local scale. In addition, even though the main conservation targets are well known, managers and practitioners lack an explicit framework in which to identify the varying requirements of site-specific conservation actions. Our aim was to provide an accurate tool for prioritizing specific local-scale conservation actions for endangered territorial birds. In this study we describe our proposed framework using a population of the endangered Bonelli’s Eagle Aquila fasciata as a case study. We identified the most relevant environmental drivers linked to demographic parameters (occupation, productivity and survival) at local scale shaping the dynamics of the Bonelli’s Eagle population in Catalonia (Spain). This information will be useful for designing specific local-scale conservation actions in eagles’ territories with low demographic parameter values. This is a good example of how applied research and achievable conservation practices are applicable to other Bonelli’s eagle populations and to those of other endangered raptors.