White-tailed Eagle Haliaeetus Albicilla Research Articles

GPS Tracking Reveals the White-Tailed Eagle Haliaeetus albicilla as an Ambassador for the Natura 2000 Network

The Natura 2000 network of protected areas is the backbone of species conservation in the European Union. We investigated whether Austrian-hatched white-tailed eagles (Haliaeetus albicilla) make particular use of this multinational network during their natal dispersal, and what habitats were of importance to the eagles. We analyzed the utilization distribution of 907,466 GPS locations from 38 dispersing white-tailed eagles using a dynamic Brownian Bridge Movement Model. Eagles ranged over a huge area of central-eastern Europe. Natura 2000 sites overlapped with 67% of the resulting 50% isopleth; i.e., a high probability of utilization of Natura 2000 areas by white-tailed eagles was found. White-tailed eagles used wetlands, waterbodies, and deciduous forests adjacent to wet habitats disproportionately often. Coniferous forests and settlements were avoided. Anthropogenically caused mortalities hardly occurred within Natura 2000 sites. Our study suggests that the Natura 2000 network is a crucial tool for conserving the white-tailed eagle. This top predator is an ambassador for the Natura 2000 idea during all life stages, and should continue to be a conservation priority of the network.

Changes in Avian Top-Predator Diet in the 21st Century in Northeast (NE) Poland

The White-Tailed Eagle (WTE) Haliaeetus albicilla is a top avian predator that has rapidly increased in numbers and range in large parts of Europe in recent decades. In Poland, over the past 30 years, it has recolonized previously abandoned areas. In 1991, the first breeding pair in a large forest complex, the Augustów Forest (Northeast (NE) Poland), was recorded. In 2022, there were 13 breeding pairs. We analyzed changes in the diet composition of WTE in 2000–2023, divided into three periods: 2000–2005, 2009–2017, and 2018–2023. Throughout the 24 years of study, birds were the most frequently recorded food item, accounting for an average of 58% of food items, followed by fish (34%) and mammals (7%). During the study period, the most numerous food items were the Northern Pike Esox lucius, Coot Fulica atra, Common Bream Abramis brama, Mallard Anas platyrhynchos, and storks Ciconia sp. These species together accounted for 52% of food items. We recorded a long-term increasing share of Northern Pike, storks, and Great Crested Grebe Podiceps cristatus. Opposite changes, with declining frequency, were found for Coots and ducks. The share of the Coot, ducks, and Great Crested Grebe, as well as the total share of food connected with lakes in the WTE’s diet, increased along the growing area of lakes in the territory of the WTE. The proportion of fish in the food did not show a relationship with the increase in the area of lakes, while the most frequently eaten fish species changed. Observed changes in food composition appear related to the settlement of the habitat-diverse areas by individual breeding pairs and changes the availability of main food categories.

Häckningsbiotop och boplatsval hos havsörn Haliaeetus albicilla på Gotland

Nest site features and habitats of the White-tailed Eagle Haliaeetus albicilla were studied in Gotland, Sweden, during 2008–2017. Here, the entire population depended on suitable trees for nesting. The mean age of the nesting trees was 173 years. Only 9% of these trees were younger than 125 years. The mean distance from nests to roads was 400 metres. The mean distance to permanent residences and recreational cottages was 1.5 km and 1.2 km, respectively. Although the nests were not located far from human activities, the eagles were very shy. Therefore, they need protected areas around the nesting trees, especially during the breeding season.

Contrasting Trends and Dynamics in the Autumn Aggregation of White-Tailed Eagles at Two Fishponds in Lithuania

The White-tailed Eagle Haliaeetus albicilla may aggregate in areas with high fish supply during their autumn movements. Here, we report on data collected between 2008 and 2019 concerning numbers of White-tailed Eagles visiting fishponds located in NE Lithuania, to the east of the Baltic Sea during the autumn months. For comparison, between 2016 and 2018 we also surveyed White-tailed Eagles at another, similarly managed fishpond, located 110 km away in SE Lithuania. The number of White-tailed Eagles at the fishponds in NE Lithuania in October through December increased nearly three-fold between 2008 and 2019. The long-term increase occurred especially in November–December and much less in October, and this, together with sudden increases in numbers in certain years, suggests possible changes in their movement patterns. We found similar numbers of assembling eagles in the two fishponds in October, but in November there were significantly more eagles at the fishponds in NE Lithuania. The size of groups in autumn and the seasonal dynamics therein may differ at different stopover sites that are similar in size, harvesting practice and located in the same region. We suggest this could be due to differences in the surrounding environment.

Early-life diet specificity is associated with long-lasting differences in apparent survival in a generalist predator.

Early-life conditions can have long-term fitness consequences. However, it is still unclear what optimal rearing conditions are, especially for long-lived carnivores. A more diverse diet ('balanced diet') might optimize nutrient availability and allow young to make experiences with a larger diversity of prey, whereas a narrow diet breadth ('specialized diet') might result in overall higher energy net gain. A diet that is dominated by a specific prey type (i.e. fish, 'prey type hypothesis') might be beneficial or detrimental, depending for example, on its toxicity or contaminant load. Generalist predators such as the white-tailed eagle Haliaeetus albicilla provide an interesting possibility to examine the relationship between early life diet and long-term offspring survival. In the Åland Islands, an archipelago in the Baltic Sea, white-tailed eagles live in various coastal habitats and feed on highly variable proportions of birds and fish. We use data from 21,116 prey individuals that were collected from 120 territories during the annual surveys, to examine how early-life diet is associated with apparent annual survival of 574 ringed and molecular-sexed eaglets. We supplement this analysis by assessing the relationships between diet, reproductive performance and nestling physical condition, to consider whether they are confounding with possible long-term associations. We find that early-life diet is associated with long-term fitness: Nestlings that are fed a diverse diet are in lower physical condition but have higher survival rates. Eagles that are fed more fish as nestlings have lower survival as breeding-age adults, but territories associated with fish-rich diets have higher breeding success. Our results show that young carnivores benefit from a high diversity of prey in their natal territory, either through a nutritional or learning benefit, explaining the higher survival rates. The strong relationship between early-life diet and adult survival suggests that early life shapes adult foraging decisions and that eating fish is associated with high costs. This could be due to high levels of contaminants or high competition for fish-rich territories. Long-lasting consequences of early-life diet are likely not only limited to individual-level consequences but have the potential to drive eco-evolutionary dynamics in this population.

Predation risk and landscape properties shape reproductive output of an endangered sea duck from two subpopulations with contrasting predation risk

Predation is the leading cause of avian reproductive failure and theory predicts clutch size reduction under high nest predation risk. However, the impact of nest predation on population dynamics is debated, and spatiotemporal variation in reproductive output is poorly understood due to the predominance of short-term, single-site studies. To this end, we investigated how island geography (size, forest cover, isolation), predation risk (White-tailed Eagle Haliaeetus albicilla abundance), climate (migration phenology, winter severity) and time trends affected early breeding success (inverse of early predation rate) and clutch size of endangered Baltic Common Eiders (Somateria mollissima). The study was conducted at two close sites (Tvärminne, Velkua) during 1991–2020. Local breeding numbers showed a similar annual decline. Interestingly, fecundity components were negatively correlated across sites: early breeding success was higher in Velkua and clutch size in Tvärminne. Island forest cover and exposure were the best determinants of early breeding success and clutch size (with only weak explanatory power for clutch size), but their effects were mediated by differential susceptibility to eagle predation risk. Clutch size increased in Tvärminne but decreased in Velkua. The former finding likely reflects increased breeder phenotypic quality due to selective disappearance at this high-predation site, whereas the latter finding may indicate increasingly compromised food intake. Only at the high-risk site did clutch size show the expected decline with increasing eagle predation risk, and the expected increase with increasing overhead protection (forest cover). We identify the least exposed forested islands, associated with the highest productivity, as prime targets of conservation.

Long-term impact on the breeding birds of a semi-offshore island-based wind farm in Åland, Northern Baltic Sea

Breeding bird populations were monitored at a wind farm in the Båtskär area of the southern Åland archipelago in 2006–2017. The area is situated in the outer archipelago and comprises four islands with six wind turbines in total. The wind turbines began operating in autumn 2007. An environmental impact assessment for the area was conducted in 2002. A control area called Stenarna, located 22 km NW of Båtskär, was used for comparison. The Båtskär area annually recorded 850–1,050 pairs of breeding birds. Four species showed significantly decreasing trends in Båtskär, namely the Common Eider Somateria mollissima, Lesser Black-backed Gull Larus fuscus, Herring Gull L. argentatus , and Black Guillemot Cepphus grylle. In Stenarna, only the Common Eider significantly decreased over the same period. The Arctic Tern Sterna paradisaea increased in both areas, while the Velvet Scoter Melanitta fusca, Red-breasted Merganser Mergus serrator, Common Gull Larus canus, Rock Pipit Anthus petrosus, and White Wagtail Motacilla alba increased in Stenarna, the control area. The Herring Gull population decline is unlikely to be related to the wind farm. However, the proximity of a wind turbine to a breeding colony of the Lesser Black-backed Gull has most likely contributed to its decline. The reason for the Black Guillemot decline in Båtskär is unknown. The decline of Common Eider in both areas may be connected to increasing predation from White-tailed Eagles Haliaeetus albicilla. Some species, such as the House Martin Delichon urbicum and auks, have benefitted from the wind farm construction. They can utilize new microhabitats created by the construction, while other species, such as the Common Eider, gain protection against predation because of human activities.

The avoidance of living in the vicinity of a top predator: the coexistence of the black stork and the white-tailed eagle in NE Poland

The black stork Ciconia nigra is a rare species of bird that inhabits old forests near wetlands. The early 21st century has brought a regress of its population in north-eastern Poland. We verified the assumption that an important reason for the observed changes was the colonization of the study area by white-tailed eagle Haliaeetus albicilla, because we observed a correlation between decreasing numbers of the black stork and increasing numbers of the eagle. Based on the long-term monitoring, we analyzed changes in the numbers and distribution of the black storks’ nests and compared the colonization of the study area by the white-tailed eagle in the most extensive forest complex in Poland. We found 42 occupied territories of storks and no eagles in 1989 within the study area. In 2019, there were just 23 stork pairs, but the population of eagles increased to 13. We found a correlation between the rate of decline of the black storks population and the increase in the white-tailed eagles. In the first half of study period, storks’ nests have been distributed randomly, after which they became clustered. The pattern of nests distribution was influenced by the increase in the population of the eagle over time, with this ensuring the aggregation of the nests of storks in places more distant from the nests of eagles. Similarly, the nearest neighbor distance of storks’ nests was dependent on distances from the nests of eagles and the shares of territory accounted for by forests. We surmise that changes in the population size of storks were induced mainly by the growth of population of eagles. Storks avoided occupying nests less than 4.6 km from the eagles’ nests. Our study suggests that the determining role can be played by fear of the predator. Overall, it must be concluded that the protection of top predators can affect other co-occurring species in unexpected ways.

First sighting of the white-tailed eagle Haliaeetus albicilla (Linnaeus, 1758) for Makwanpur District, Nepal

The white-tailed eagle Haliaeetus albicilla is a rare winter visitor to Nepal and it has been previously recorded from Chitwan, Kathmandu, Nawalparasi, Bardiya, Sunsari and Kaski districts of Nepal. Here, we present the first-ever record of the white-tailed eagle for the Makwanpur District of Nepal. During the bird survey by line transect method, we observed a single juvenile of the species soaring over the Manahari River on 29 January 2022. Loss of habitat, illegal fishing, human disturbance, extraction of boulders, gravel, sand and water pollution were the major threats to birds observed during the survey period. In order to overcome these threats, conservation awareness programs about the importance of birds, effective law enforcement, and regular monitoring should be carried out in the study area.

Occurrence and Behaviour of White-Tailed Eagles Haliaeetus albicilla in Great Cormorant Phalacrocorax Carbo Sinensis Colonies in Countries around the Baltic Sea

The recovery of the Baltic White-tailed Eagle Haliaeetus albicilla population since the 1980s is a conservation success story. However, the re-establishment of this predator in coastal and lake areas appears to affect Great Cormorants Phalacrocorax carbo during the breeding season. We collated published and unpublished records of White-tailed Eagle occurrence and interactions with Cormorant colonies as well as records of Cormorant anti-predator responses and effects on Cormorant breeding performance. We found evidence for immediate direct effects (mainly kleptoparasitism, predation of eggs and offspring) and indirect effects (facilitating nest predation by mainly gulls and corvids). Repeated disturbance from hunting White-tailed Eagles was also inferred to trigger changes in selection of nest sites, to cause complete abandonment of colonies and lead to regional redistributions of breeders. However, there are also observations of ‘unproblematic’ coexistence with White-tailed Eagles breeding inside Cormorant colonies. There is some evidence to suggest that nesting opportunities for Cormorants may become further restricted as White-tailed Eagle numbers continue to increase, and we argue that this – in some regions – will impose limitations on the distribution and size of breeding populations of Cormorants.

Conservation measures for the Caspian Tern Hydroprogne caspia at the largest colony in Sweden

We present conservation actions during 2007–2020 as part of the national Caspian Tern Hydroprogne caspia species action plan at Stenarna in the Björn archipelago, Uppland, the largest colony in Sweden. We applied a combination of monitoring, research, and management measures conducted within an adaptive approach framework, using both established and novel techniques. The implementation of conservation measures led to increased breeding success, from 0 fledglings per pair in 2007 to 1.3 in 2020. A surveillance video camera installed in 2009 aided in monitoring efforts and also revealed predation by Herring Gull Larus argentatus and White-tailed Eagle Haliaeetus albicilla, leading to species-specific control strategies. Management of the island and surrounding archipelago, including hunting of invasive American mink Mustela vison, vegetation removal, and habitat restoration after a severe storm, have also been instrumental to the success of the project. Implementation of projects such as this have the potential to improve conditions for continued viability of endangered species in a changing world and are likely to be useful to other conservation practitioners.

Role of three bird species in the life cycle of two Sarcocystis spp. (Apicomplexa, Sarcocystidae) in the Czech Republic.

Birds are one of the groups involved in the development of Sarcocystis Lankester (1882), serving either as intermediate or definitive hosts. The white-tailed sea eagle Haliaeetus albicilla (Linnaeus, 1758), red kite Milvus milvus (Linnaeus, 1758) (both Accipitriformes) and common starlings Sturnus vulgaris Linnaeus, 1758 (Passeriformes) were examined to elucidate their participation in the development of Sarcocystis, as well as to determine the specific identity of the parasites based on morphological and especially molecular analyses. In 2020–2021, one white-tailed eagle, one red kite and five common starlings were parasitologically examined for the presence of Sarcocystis using flotation centrifugation coprological method and by wet mounts of intestinal mucosa scrapings and/or muscle samples. Positive samples were processed by light microscopy, histologically and followed molecularly at four genetic markers (18S rRNA, 28S rRNA, ITS1 and cox1). The white-tailed eagle harboured oocysts/sporocysts of S. arctica Gjerde et Schulze, 2014 in the intestinal mucosa, while the intestinal mucosa of the red kite and breasts and leg muscles of one common starling were positive to S. halieti Gjerde, Vikøren et Hamnes, 2018. Sequences from eagle shared 99.6–100% identity with each other and S. arctica in the red fox (V. vulpes Linnaeus, 1758) from the Czech Republic. Sequences from the common starling and red kite shared 100% identity with each other and with S. halieti in the great cormorant (P. carbo [Linnaeus, 1758]) from Lithuania and H. albicilla from Norway. The white-tailed sea eagle might act as definitive host of S. arctica, whereas the common starling and red kite represent intermediate and potential definitive hosts, respectively, for S. halieti.

Spatial and temporal variation in breeding performance in the increasing White-tailed Eagle Haliaeetus albicilla population to the east of the Baltic Sea

ABSTRACT Capsule We found no evidence of decreased reproductive performance of the White-tailed Eagle Haliaeetus albicilla, despite ongoing population increases in an environment characterized by different types of utilized habitats. Aim To characterize temporal and spatial variations in several components of breeding performance in an increasing White-tailed Eagle population. Methods The breeding performance and number of pairs located in the region east of the Baltic Sea was monitored between 2005 and 2020. We analysed the trends in the numbers of pairs and several reproduction parameters for 16 years, and compared variation in breeding performance in four different habitats through application of generalized linear (mixed) models. Results The number of White-tailed Eagle pairs increased three-fold locally between 2005 and 2020, but we found no evidence for a deterioration in breeding performance parameters (nesting success, brood size, proportion of females among nestlings, body condition of nestlings). The probability of successful nesting, nestling sex and number of nestlings in a brood were found to be similar between pairs associated with different habitats, ranging from coastal lagoons to natural waterbodies within an inland landscape. The body condition of the nestlings, however, was habitat-dependent, with the best body condition evident in nestlings reared near the Curonian Lagoon. Conclusion Results indicate that the abundance of this predator population will continue to grow in the region east of the Baltic Sea.

Head and body orientation of the White Stork Ciconia ciconia during incubation: effect of wind, apex predators and power lines

Incubation behaviour is essential for understanding the reproductive success in birds. For example, the orientation of the bird is important for reducing incubation costs associated with wind or sun, but on the other hand can be modified by the perceived risk of predation. We studied the body position of incubating White Stork Ciconia ciconia in eastern Poland using a small unmanned aerial vehicle (drone). The head and body orientation of the incubating storks was non-random and modified by natural factors, mainly wind direction and speed, but also by the presence of an apex predator, the White-tailed Eagle Haliaeetus albicilla. However, head orientation during incubation in nests located on electricity poles was also modified by the presence of the power lines, probably due to disturbance in the magnetic field detected by birds. Surprisingly, although the positioning of incubating birds (mainly females) is very important for the detection of predators and for reducing energy costs, these have not previously been studied. New technologies, such as drones, make it possible to collect new, extensive information on the incubation behaviour of birds.

Parental Investment Under Predation Threat in Incubating Common Eiders (Somateria mollissima): A Hormonal Perspective

Predation risk affects the costs and benefits of prey life-history decisions. Predation threat is often higher during reproduction, especially in conspicuous colonial breeders. Therefore, predation risk may increase the survival cost of breeding, and reduce parental investment. The impact of predation risk on avian parental investment decisions may be hormonally mediated by prolactin and corticosterone, making them ideal tools for studying the trade-offs involved. Prolactin is thought to promote parental care and commitment in birds. Corticosterone is involved in allostasis and may either mediate reduced parental investment (corticosterone-fitness hypothesis), or promote parental investment through a reallocation of resources (corticosterone-adaptation hypothesis). Here, we used these hormonal proxies of incubation commitment to examine the impact of predation risk on reproduction in common eiders (Somateria mollissima) breeding in the Baltic Sea. This eider population is subject to high but spatially and temporally variable predation pressure on adults (mainly by the white-tailed eagle Haliaeetus albicilla and introduced mammalian predators) and nests (by the adult predators and exclusive egg predators such as hooded crows Corvus cornix). We investigated baseline hormonal levels and hatching success as a function of individual quality attributes (breeding experience, female and duckling body condition), reproductive investment (clutch weight), and predation risk. We expected individuals nesting in riskier environments (i.e., on islands where predation on adults or nests is higher, or in less concealed nests) to reduce their parental investment in incubation, reflected in lower baseline prolactin levels and either higher (corticosterone-fitness hypothesis) or lower (corticosterone-adaptation hypothesis) baseline corticosterone levels. Contrary to our predictions, prolactin levels showed a positive correlation with nest predation risk. The unexpected positive relationship could result from the selective disappearance of low-quality females (presumably having low prolactin levels) from risky sites. Supporting this notion, female body condition and hatching success were positively correlated with predation risk on females, and baseline prolactin concentrations were positively correlated with duckling body condition, a proxy of maternal quality. In line with the corticosterone-adaptation hypothesis, baseline corticosterone levels increased with reproductive investment, and were negatively associated with nest predation risk. Hatching success was lower on islands where nest predation risk was higher, consistent with the idea of reduced reproductive investment under increased threat. Long-term individual-based studies are now needed to distinguish selection processes occurring at the population scale from individually plastic parental investment in relation to individual quality and variable predation risk.

Eiders, nutrients and eagles: Bottom-up and top-down population dynamics in a marine bird.

The main objective of this long-term study (1978-2016) was to find the underlying factors behind the declining trends of eider Somateria mollissima in the Baltic/Wadden Sea. Specifically, we aimed at quantifying the bottom-up effect of nutrients, through mussel stocks, on reproduction and abundance of eider, and the top-down effects caused by white-tailed eagle Haliaeetus albicilla predation. Bottom-up effects increase marine primary productivity with subsequent effects on food availability for a major mussel predator. Top-down effects may also regulate eider populations because during incubation female eiders are vulnerable to predation by eagles. Our structural equation modelling explained a large percentage of the variance in eider abundance. We conclude that the Baltic/Wadden Sea eider population was regulated directly by white-tailed sea eagle predation on incubating females and indirectly by the amount of nutrients in seawater affecting both mussel stocks and the breeding success of eiders, reflecting density dependence. These findings may explain the decreasing trend in the Baltic/Wadden Sea eider population during the last decades as an additive effect of top-down and bottom-up factors, and likely as an interaction between them.

Habitat use by post-fledging white-tailed eagles shows avoidance of human infrastructure and agricultural areas

Habitat use studies provide invaluable information for the conservation of species that suffer from habitat loss or degradation. We used satellite telemetry to study the habitat use of white-tailed eagles (Haliaeetus albicilla) in relation to six habitat classes (artificial surfaces, agricultural areas, forests, semi-natural areas, wetlands and waterbodies) and five forest age classes (0–9, 10–19, 20–59, 60–99 and ≥ 100 years old) during the post-fledging period in Finland. The post-fledging period, defined here as the period between fledging and dispersal from the natal area, is a critical life-history stage. Our primary objective was to provide information that could be integrated into landscape planning, including wind-energy development (which poses a threat to white-tailed eagles). We found that the habitat classes that were selected by the young white-tailed eagles were forests, semi-natural areas (i.e., transitional woodland and bare rock) and wetlands. When using forests, the eagles selected stands of 0–9 years old, presumably due to the use of retention trees surrounded by a clear-cut as perching sites. Conversely, the habitat classes that were avoided were artificial surfaces, agricultural areas and (the immediate vicinity of) waterbodies. We conclude that the conversion of natural habitats into built and agricultural areas is detrimental to young white-tailed eagles because it reduces habitat availability. They, however, appear to be capable of using forests recently impacted by forestry if perch trees are present. Careful landscape planning is needed to protect priority habitats and avoid conflicts with an expanding white-tailed eagle population (e.g., by building wind farms in areas already environmentally disturbed).

Changes in the Trophic Structure of the Vertebrate Predator Community in the Cold Season in Belarussian Paazerje (Northern Belarus) in Relation with Emphasis on Depopulation of the Wild Boar, Sus scrofa (Artiodactyla, Suida)

Anthropogenic disturbances often alter patterns of community functioning. Along that, how interacting species respond to these changes remains poorly understood. In 1972–2019, we studied the trophic structure of the vertebrate predator community in coniferous-small-leaved forests of Belarussian Paazerje (Northern Belarus). Since 2013, large scale depopulation of wild boars Sus scrofa has been started in Belarus as a measure to reduce a circulation of the African swine fever (ASF). It was found that the community consisted of four trophic guilds including small rodent consumers, bird consumers, scavengers, and ungulate consumers. The pronounced shifts in dietary compositions of three scavengers (the raccoon dog Nyctereutes procyonoides, golden eagle Aquila chrysaetos and white-tailed eagle Haliaeetus albicilla) after a decrease in an abundance of wild boar carrion was revealed. Along that, the average value of the dietary similarity between investigated species stayed the same.

Dynamics of the Onset of White-Tailed Eagle (Haliaeetus albicilla) Breeding in the Central Part of the Volga–Kama Region and Possible Explanations

This work is aimed at determining the onset of breeding of the White-tailed Eagle and the reasons that affect its breeding phenology in the central part of the Volga–Kama region (Republic of Tatarstan, together with the adjacent areas of the republics of Chuvashia and Udmurtia, as well as Samara and Ulyanovsk oblasts). In the Republic of Tatarstan, the bulk of data were obtained in 2011–2016; in Ulyanovsk and Samara oblasts, in 2012; in the Republic of Chuvashia, in 2013, 2015, 2016; and in Udmurtia, in 2016. An analysis of the onset of breeding was carried out on the basis of photo records of the White-tailed Eagle nests with nestlings primarily at ages of 30–60 days and some younger than 30 days, in 2011–2016. The age of nestlings was determined by the photo tables comparing the degree of development of their plumage. When establishing the date of the first egg laying, the age of the elder (or the only) nestling and the incubation time, which amounts to 37 days, were taken into account. In total, 119 cases of breeding were analyzed. For additional control of calculations concerning the earliest periods of breeding, at the beginning of the breeding season, on February 23, 2015, distant observations of a group of 16 nests were carried out using optical devices along the upper reaches of the Kuibyshev reservoir. More precise data on the dates of egg laying were also obtained using a surveillance camera at an eagle nest in the Volga–Kama Biosphere Nature Reserve. According to the results of calculations, the period of the first egg laying extends from February 22 to April 11 (n = 119). Most of the clutches (70.6%, n = 84) are laid in the period from February 22 to March 15, and the maximum occurs in the first five days of March (26.05%, n = 31). A comparison with previously published data shows that, on average, the eagles start breeding half a month earlier than they did in the 20th century. In our opinion, the shift towards earlier breeding dates is primarily caused by the presence of artificial food supply at local wintering sites and increased species numbers in the Volga–Kama region. The White-tailed Eagle’s status in the region partially changed from the migrating breeder to resident breeder. The distances from the breeding territories to the wintering grounds with abundant of forage shortened significantly. The influence of climate warming on the time of egg-laying cannot be excluded either.

Diet and breeding habitat preferences of White-tailed Eagles in a northern inland environment

Many apex predator populations are recolonizing old areas and dispersing to new ones, with potential consequences for their prey species and for livestock. An increasing population of the White-tailed Eagle (Haliaeetus albicilla) has settled north of the Arctic Circle in northern Finland, mainly at two big water reservoirs but also in areas with mainly terrestrial habitat. We examined nesting habitat preferences and prey use of White-tailed Eagles in this environment, where reindeer husbandry is a traditional livelihood and concerns are rising that the growing White-tailed Eagle population poses a threat to reindeer calves. Lakes, peat bogs, and marshlands were preferred habitats in the nesting territories. Fish constituted 64.3% of the identified prey items, with birds accounting for 28.5% and mammals 7.2%. The nesting territory habitat within a 10 km radius and the latitude influenced the prey composition at both the group and species level. The occurrence of reindeer calves as prey increased with latitude but was not associated with any habitat. Knowledge of the diet and territory preferences can be used to predict future dispersal and local prey use of this species. Nesting White-tailed Eagles do not seem to pose a threat to traditional reindeer herding, but further research is needed regarding non-breeding sub-adults and whether the White-tailed Eagles actually kill reindeer calves or simply exploit their carcasses.