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.

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.

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.

[The decline of one of the most threatened European birds of prey: 41 years of observations on the Lanner, Falco biarmicus in Sicily]

[The results of a research on Lanner in southern Sicily, carried out between 1978 and 2018, are reported. 32 Lanner nesting territories have been taken into account, from sea level up to 1200 m of altitude. Until 2005, there were about 25 nesting pairs in the area; but in the following years there was a steady decline. At least 16 sites have been gradually abandoned because of human persecution and, at a lesser degree, of the interference with the Peregrine falcon, Falco peregrinus, and the Bonelli’s eagle, Hieraaetus fasciatus. At present, the number of Lanner pairs breeding in the study area is around 12. From 120 nesting attempts followed, 216 youngs fledged, with a productivity of 1.80, with breeding success of 1.98, fledging rate of 2.40. Out of 109 nests in which there was egg laying, 90 were successful. Out of successful nests, 11 fledged 1 young (12.2%); 37 nests 2 youngs (41.1 %); 37 nests, 3 youngs (41.1%); 5 nests, 4 youngs (5.6%). The number of pairs that have laid eggs, in relation to the number of the monitored nests, was of 90.8%. The ratio between the number of nests in which youngs were raised and the number of pairs that laid their eggs was 88.1%. The ratio between the number of nests from which youngs fledged and the number of breeding pairs was 93.7%.The number of successfully breeding nests, in relation to the number of monitored nests, was 75%. As regards the diet, birds represent Lanner’s most frequent preys. Out of the 415 preys identified, 383 (92.3%) are made up of birds, 29 (7%) by small mammals, 3 (0.7%) by reptiles. In addition to human persecution, the population of Lanner in Sicily is influenced by interspecific competition, particularly with the Peregrine falcon; but in 2 cliffs, about 1 km long and with a substantial wealth of prey, both falcons have been successfully reproducing for over 10 years]. [Article in Italian]