Individual acoustic monitoring of the European Eagle Owl Bubo bubo

The Eagle Owl Bubo bubo is cited in Annex I of the Birds Directive of the European Union. Europe's biggest owl is extremely sensitive to human presence and needs special conservation measures. The present paper aims to show that monitoring of individuals by bioacoustic methods can be relevant to understanding population dynamics. Our study investigates the possibility of identifying a vocal signature in the wild-recorded calls of male and female Eagle Owls, and assesses the potential use of these signatures for long-term monitoring of individuals in the field. We show that both males and females of a given population can be identified individually on the basis of their calls. Our results also show that, regardless of the sex, most of the individuals recorded in the first year of the investigation may be identical to those recorded in the same places the year after. This bioacoustic approach could thus be used in studies of site fidelity.     

Costs and benefits of breeding in human-altered landscapes for the Eagle Owl Bubo bubo

We studied a population of 23–25 Eagle Owl Bubo bubo pairs between 1994 and 2000 in a 1330-km² study plot in the central-eastern Italian Alps. Compared to random sites, territories were located at lower elevation and closer to intensively cultivated-urbanized valley floors. Early laying was associated with low elevation and negatively affected productivity. Diet was dominated by rats, hedgehogs and dormice ( n  = 978 prey items), all of them typical of low-elevation habitats. Higher productivity was associated with a higher proportion of rats in the diet of individual pairs. Low availability of rats resulted in a more diverse diet, in turn associated with low productivity. Territories were occupied every year in a non-random fashion, and those most occupied were characterized by higher productivity and higher occurrence of the favoured prey types in the diet, suggesting they were of superior quality. Eagle Owls also paid a cost associated with nesting near human-altered habitats: the main cause of mortality reported to local authorities was electrocution. This is an increasing cause of death for many European populations and may be a cause for conservation concern. Human persecution is also an important cause of mortality in some parts of the European range. Apart from such costs, the study population appeared to have adapted well to the proximity of humans: estimates of density and productivity were comparable to those recorded elsewhere in Europe. The pattern found in our population also held at higher spatial scales: data from 17 European populations showed density to be highest in low-elevation, human-altered landscapes.     

Ecological factors influencing disease risk in Eagle Owls Bubo bubo

In this study we assessed whether local habitat features and host population density influenced disease risk in Eagle Owl Bubo bubo fledglings. Measures of immune defence (concentrations of circulating white blood cells), prevalence of three parasite types (a blood parasite Leucocytozoon ziemanni , an insect Carnus haemapterus , and a tick Rhipicephalus sp.) and total number of parasite species were used to quantify disease risk. We tested the hypotheses that disease risk in fledglings was higher in nests located in areas with higher length of and proximity to watercourses (as a higher abundance and viability of parasites and vectors occur in wetter areas), higher cover of forest (as forest moistness and humidity can favour higher vector and parasite proliferation), higher habitat diversity (as environmental heterogeneity increases the pool of potential vectors and parasites) and higher local owl population density (as disease transmission might be density-dependent). The clearest relationship was with the proximity of freshwater, although the other hypotheses were also partially supported. Concentrations of white blood cells, the number of parasite species and, weakly, the prevalence of Carnus haemapterus were all higher in nests closer to watercourses. The prevalence of blood parasites increased with the cover of forested areas. Fledglings from nests located in more diverse habitats had higher white blood cell concentrations and showed higher prevalence of blood parasites. Finally, local host population density was positively correlated with the prevalence of blood parasites. The results suggest the existence of complex and interrelated links between ecological parameters and three different measures of disease risk, and highlight the importance of immunological approaches to assess disease risk at an intraspecific level.     

Limited prospecting behaviour of juvenile Eagle Owls Bubo bubo during natal dispersal: implications for conservation

Capsule Features of the breeding population and temporary settlement area influence the behaviour of Eagle Owls Bubo bubo prospecting for breeding sites during natal dispersal.

Aims To understand how prospecting behaviour during natal dispersal is affected by (i) the main characteristics of the breeding and dispersing portions of the population and (ii) main prey availability.

Methods We explored the ten-year dynamics and characteristics of radio-tagged breeders and dispersers of an Eagle Owl population.

Results During the first years following natal dispersal there was little prospecting behaviour of nesting sites and birds remained mainly within non-breeding settlement areas, bordering the sector occupied by the breeding population. Settlement areas had an abundant food supply, and low intraspecific competition and mortality. We suggest that these features of the settlement areas may reduce the willingness of individuals to search for breeding sites and may have the potential to impact on the viability of breeding populations.

Conclusion From a conservation perspective, the lengthy use of the temporary settlement areas by juvenile Eagle Owls suggests that the sites should be considered as important as the breeding areas when planning conservation strategies. Reducing juvenile mortality in settlement areas may represent an overlooked conservation strategy for long-lived species and may have a crucial effect on the viability some animal populations.     

The Sound Suppression Characteristics of Wing Feather of Owl (Bubo bubo)

Many species of owls are able to fly noiselessly,and their wing feathers play an important role for the silent flight.In this paper,we studied the sound suppression mechanism of the eagle owl (Bubo bubo) by Stereo Microscope (SM),Scanning Electron Microscopy (SEM) and Laser Scanning Confocal Microscope (LSCM).To investigate the effects of special characteristics of wing feather on owl silent flight,the acoustic properties,including the sound absorption coefficient and flight noise,were compared between the eagle owl and common buzzard (Buteo buteo).The results show that the eagle owl generates lower noise than common buzzard during flight,and its wing feather has better sound absorption properties.The leading edge serration and trailing edge fringe can improve the pressure fluctuation of turbulence boundary,and suppress the generation of vortex sound.The elongated distal barbules form a multi-layer grid porous structure which also has an effect on sound absorption.This research not only can give the inspiration for solving the aerodynamic noise of aircraft and engineering machine,but also can provide a new idea for the design of low-noise devices.     

Social status influences microhabitat selection: breeder and floater Eagle Owls Bubo bubo use different post sites

Social status can be reflected in many aspects of an individual’s behaviour and ecology, including habitat use and conspecific interactions. In territorial species where at least two social groups – breeding birds and non‐territorial floaters – are recognized, the diverse tasks associated with territorial ownership can lead territory holders to behave differently from the non‐territorial part of the population. Territory holders defend their breeding area and reproduce, whereas floating individuals are dispersing and lead a more transient life, during which they do not show any territorial behaviour even when settling in a more or less fixed area (known as the stop phase). As social interactions are based on visual and vocal cues, the use of specific sites for sending and/or receiving signals can be a crucial choice in an animal’s life. By analysing the post‐site selection of Eagle Owl Bubo bubo breeders and floaters during their nocturnal activity, we found that: (1) territory holders selected more visible and dominant posts than non‐territorial floaters; (2) the choice of posts made by floating individuals did not differ between the wandering and stop phases of dispersal; and (3) floating females intruded more frequently than floating males within a breeder’s home‐range. These findings highlight the fact that two social strategies are possible within the same species, depending on an individual’s social status and its related tasks. Breeders could take advantage of visible locations to declare their status as territory holders, whereas floaters could benefit from a more secretive life to wander unnoticed among occupied territories. This secretive life would help floaters to reduce the risks associated with conspecific aggression. Finally, the greater occurrence of floating females within breeders’ home‐ranges can be explained by the fact that female incursions in a breeder’s home‐range are less risky than male intrusions.     

Fostering orphan Eagle Owls (Bubo bubo) as a successful conservation technique: A first for the species

For many species, the artificial raising of orphaned nestlings is a time and cost-prohibitive task, usually accompanied by low survivability. The introduction of orphaned nestlings to other natural nests was found to be a successful technique wherein fostered nestling(s) developed better in the wild and imprinting on humans is avoided. To date, the number of diurnal species in which induced alloparenting has been conducted is limited to several eagle species, falcons, buzzards, and vultures. In the owls, it has only been demonstrated to work in two species, but the eagle owl has not been studied in this aspect. Eagle Owls, amongst the largest of the owls with a geographic distribution stretching across Europe and Asia, are a favored species in the wildlife trade, and many a nestling is removed from the nest. In Israel, when reported or rescued, the nestlings are removed to the wildlife hospital where they are rehabilitated and then introduced into a wild nest with similarly aged nestlings. From 2009 to 2021 we conducted 44 successful adoptions of Eagle Owl orphans into active, wild nests. This success stresses the importance of our work as a conservation tool for the preservation of an apex predator across its breeding range.     

Vocal behaviour and neighbour spatial arrangement during vocal displays in eagle owls (Bubo bubo)

We quantified temporal and spatial patterns of adult eagle owl Bubo bubo vocal behaviour throughout an entire year. The duration of adult eagle owl vocal displays showed significant differences during different periods of the year: there was one major peak in the pre-laying period, when duets of mates were also more frequent. The daily distribution of adult vocalizations showed a similar pattern among the different periods, with vocal activity being most intense at sunset and sunrise. Analyses of the characteristics of call posts showed that the choice of such focal points was guided by the trade-off between the need to defend the territory and within-pair communication inside the core areas, as well as efficient communication with neighbours.     

雕鸮（Bubo bubo）和长耳鸮（Asio otus）体内金属元素含量的测定

采用ICP-AES电感耦合等离子光谱仪对来源于北京地区的长耳鸮(Asio otus)和雕鸮(Bubo bubo)体内的金属元素Cr,Pb,Co,Cd,Ni和Mn含量进行了检测.长耳鸮各组织中的重金属含量,仅Cd(p=0.000)在不同组织中有显著性差异,雕鸮各组织中Cr(p=0.002),Ni(p=0.000),Co(p=0.009),Cd(p=0.010), Mn(p=0.002)在不同组织中有显著性差异.Cr在长耳鸮的肾脏中含量最高,而在雕鸮各组织中则是在脑中的含量最高.Cd的含量在各种金属中是最少的,而Mn的含量最高.两种鸮类中,Ni在长耳鸮胸羽中的含量高于其他组织,而在雕鸮体内则是在脑中的含量高于其他组织.Co在长耳鸮的肾脏中含量最高,雕鸮的脑中含量最高,肾脏次之.并且实验还发现无论是长耳鸮还是雕鸮,背羽都是检测重金属的最佳选择.     

雕鸮消化系统形态学的初步研究

对一只雕消化系统的形态学作了初步的观察与研究,结果表明:雕舌呈鞋底形,舌根分叉,叉粘膜上具有尖端指向后方的栉状突;食管宽而扁,无明显可见的嗉囊;肌胃无明显的类角质膜;肠道长是体长的2.05倍,小肠较发达,长970.5 mm,占肠道总长的75.7%,具有较发达的双侧盲肠。并与蛇雕、毛脚、黑鸢的消化系统进行了比较。     

青海门源地区大(狂鸟)和雕鸮的食性比较

1999～2002年的6～8月份,在青海门源地区收集了大(狂鸟)和雕鸮的吐弃块(pellets)和残留食物(food remains),带回实验室进行分检鉴定、研究分析.大(狂鸟)食物中共有736个猎物,其中高原鼢鼠28只、高原鼠兔139只、甘肃鼠兔142只、田鼠科动物422只、雀形目鸟类4只、香鼬1只;各猎物对大(狂鸟)食物的生物量贡献率分别为14.26%、40.79%、17.39%、26.99%、0.22%、0.35%.雕鸮食物中共有330个猎物,其中高原鼢鼠17只、高原鼠兔77只、甘肃鼠兔44只、田鼠科动物183只、雀形目鸟类2只、红脚鹬2只、高原兔5只;各猎物对雕鸮食物的生物量贡献率分别为11.83%、30.87%、7.36%、16.00%、0.15%、0.62%、33.17%.雕鸮的食物生态位宽度与大(狂鸟)的食物生态位宽度相近,食物生态位高度重叠,但是它们捕食同种猎物的比例显著不同.     

Brightness variability in the white badge of the eagle owl Bubo bubo

The application of modern spectrometry to the study of avian colour variability has revealed ignored patterns of colour variation such as male‐biased sexual dichromatism and seasonal variability in the plumage. However, the variation in the achromatic property of such traits, that is in the total light reflectance of the spectrum (i.e., brightness), has commonly been overlooked. The evolution of signals based on brightness should be favoured in those species that are active when light is scarce, i.e. at dawn and dusk. The eagle owl Bubo bubo is monogamous and apparently monomorphic in plumage‐coloration. In this species, sexual and territorial call behaviour is mainly performed at dawn and dusk, during which a white patch on the throat is repeatedly exposed at each call. We measured the total light reflectance of the feathers of this badge in 39 eagle owl specimens from museum collections. We found seasonal variability and sexual dichromatism in the brightness of the plumage badge. The total reflectance of this trait peaked during the territorial‐mating period. Moreover, females showed higher values of brightness than males, in agreement with the reversed body size dimorphism present in this and many other raptor species. Finally, female but not male body size was positively correlated with white badge reflectance.     

Brightness variability in the white badge of the eagle owl Bubo bubo

The application of modern spectrometry to the study of avian colour variability has revealed ignored patterns of colour variation such as male-biased sexual dichromatism and seasonal variability in the plumage. However, the variation in the achromatic property of such traits, that is in the total light reflectance of the spectrum (i.e., brightness), has commonly been overlooked. The evolution of signals based on brightness should be favoured in those species that are active when light is scarce, i.e. at dawn and dusk. The eagle owl Bubo bubo is monogamous and apparently monomorphic in plumage-coloration. In this species, sexual and territorial call behaviour is mainly performed at dawn and dusk, during which a white patch on the throat is repeatedly exposed at each call. We measured the total light reflectance of the feathers of this badge in 39 eagle owl specimens from museum collections. We found seasonal variability and sexual dichromatism in the brightness of the plumage badge. The total reflectance of this trait peaked during the territorial-mating period. Moreover, females showed higher values of brightness than males, in agreement with the reversed body size dimorphism present in this and many other raptor species. Finally, female but not male body size was positively correlated with white badge reflectance.     

On the diet of the Pharaoh Eagle Owl,Bubo ascalaphus (Savigny, 1809), in Qatar,with an overview of its feeding habits

The diet of Bubo ascalaphus in Qatar was assessed based on pellets collected from the first known nesting site of the species in the country. The pellets contained a total of 68 prey items, representing 9 different species: 4 mammals, 1 bird, 1 reptile, and at least 3 scorpions. Mammals clearly comprised the major food source (89.7% and 97.7% in frequency and biomass respectively). Our data suggest that Pharaoh Eagle Owls are opportunistic predators that feed on a variety of prey depending on their temporal/spatial availability, which is consistent with previous studies. A literature review clearly suggests that Eagle Owls in arid to semi-arid environments are opportunistic predators with small mammals being their main prey. Predation on migrating Blue-cheeked Bee-eaters Merops persicus supports this hypothesis.     

The Coccidian Caryospora bubonis in the Great Horned Owl (Bubo virginianus)1

The life cycle of Caryospora bubonis was studied in the Great Horned Owl. Owls fed sporulated oocysts became patent on days 8–13, and peak oocyst production occurred between days 14 and 18. Owls fed infected mice became patent on days 8–10, and peak oocyst production occurred between days 9 and 13. The reduction in length of the life cycle in owls fed infected mice provides evidence that both indirect and direct life cycles can occur in this species and suggests that parallels exist in the lives of various isosporid, eimeriid, and other coccidia that may not have been sufficiently appreciated in the past.     

Predictive models of habitat preferences for the Eurasian eagle owl Bubo bubo: a multiscale approach

Habitat preference of eagle owls Bubo bubo were examined through comparing habitat composition around 51 occupied cliffs and 36 non-occupied cliffs in Alicante (E Spain). We employed Generalized Linear Models to examine patterns of habitat preference at three different spatial scales: nest site (7 km²), home range (25 km²), and landscape (100 km²). At the nest site scale, occupied cliffs were more rugged, had a greater proportion of forest surface in the surroundings, and were further from the nearest paved road than unoccupied cliffs. Additionally, probability of having an occupied cliff increased when there was another occupied territory in the surroundings. At both the home range scale and the landscape scale, high probabilities of presence of eagle owls were related to high percentages of Mediterranean scrubland around the cliffs, which are the preferred habitat of European rabbits Oryctolagus cuniculus , the main prey of the owls. We suggest a hierarchical process of habitat selection in the eagle owl concerning suitable trophic resources at the broadest scales and adequate sites for breeding and roosting at the smallest scale. However, it should be noted that some structural features such as the proximity of roads were not necessarily avoided by the owls, but their presence were possibly constrained by systematic killing of individuals. Our paper provides new evidence for the requirement of multi-scale approaches to gain insight into both the different limiting factors for the persistence of populations and the role of individual perception of the environment in the evolution of habitat selection.