White-tailed Eagle Haliaeetus Albicilla Research Articles

Parentage Analysis in the White-Tailed Eagle Haliaeetus albicilla: Are Moulted Feathers from Nest Sites a Reliable Source of Parental DNA?

Existing parentage analyses of large raptors have mostly used naturally shed feathers as a source of DNA. There is evidence that eagle nests are sometimes visited by conspecifics. Are these visitors involved in extra pair-paternity? More than 400 feather samples of nestlings and full-grown White-tailed Eagles were obtained in May at 13 nest sites in the Czech Republic, mainly during the years 2010–2016. The samples were genotyped at six microsatellite loci to determine the identity and number of individuals occurring at each nest site and to test genetic monogamy. In the end, 110 unique genotypes of possible parents were identified from moulted feathers found below nests and were used in a parentage analysis together with 86 offspring genotypes. Interestingly, more than two adult genotypes were sampled from shed feathers in one-third of 64 checks of 11 nests, but nest success was not affected by the number of genotypes. No case of extra-pair paternity was recorded. The results showed that feathers of individuals other than the parent pair can be found below nests of White-tailed Eagles during a single breeding season, and the identity of parents at individual nests can change even during seven years of study, which is inconsistent with the expected longevity, lifelong monogamy and presumed territoriality of White-tailed Eagles. We cannot recommend DNA sampling of nesting pairs on the basis of feathers found below eyries, because the most likely parent was recorded in the appropriate year only in 58% of cases with this method.

High-Resolution Modeling of Uplift Landscapes can Inform Micrositing of Wind Turbines for Soaring Raptors

Collision risk of soaring birds is partly associated with updrafts to which they are attracted. To identify the risk-enhancing landscape features, a micrositing tool was developed to model orographic and thermal updraft velocities from high-resolution remote sensing data. The tool was applied to the island of Hitra, and validated using GPS-tracked white-tailed eagles (Haliaeetus albicilla). Resource selection functions predicted that eagles preferred ridges with high orographic uplift, especially at flight altitudes within the rotor-swept zone (40–110 m). Flight activity was negatively associated with the widely distributed areas with high thermal uplift at lower flight altitudes (<110 m). Both the existing wind-power plant and planned extension are placed at locations rendering maximum orographic updraft velocities around the minimum sink rate for white-tailed eagles (0.75 m/s) but slightly higher thermal updraft velocities. The tool can contribute to improve micrositing of wind turbines to reduce the environmental impacts, especially for soaring raptors.

Spatial and temporal variations in the White-tailed Eagle Haliaeetus albicilla breeding diet revealed by prey remains

ABSTRACT Capsule: Despite its population increase, the White-tailed Eagle Haliaeetus albicilla has not become food-limited, and does not pose a serious threat to birds of conservation concern in the region east of the Baltic Sea. Aims: We aimed to test variations in the main prey groups and dietary niche breadth of White-tailed Eagles through the years and along an environmental gradient as well as to evaluate the extent of predation on bird species of conservation concern. Methods: Prey remains were collected during nestling ringing from successful nests located in Lithuania. Results: The frequency of the prey groups varied along an environmental gradient, with a general pattern of increasing avian prey consumed by pairs breeding in areas with less abundant aquatic habitats. The frequency of alternative prey (i.e. terrestrial birds, mammals) and dietary niche breadth did not increase between 2005 and 2018 and during which time the White-tailed Eagle population nearly doubled. Instead, the occurrence of Northern Pike Esox lucius remains, which was the most frequent single prey species, increased throughout the study period. Bird species of conservation concern constituted only a small fraction of all the prey identified. Conclusions: The White-tailed Eagle has not become more dependent on alternative prey despite its population increase.

Sex- but not age-biased wind turbine collision mortality in the White-tailed Eagle Haliaeetus albicilla

Several studies on wind turbine collision mortality in raptors suggest a bias towards adult birds, while sex-biased mortality has not yet been documented. We compared collision mortality in relation to all known causes of mortality and in relation to demographic data for the German population of the White-tailed Eagle and found collision mortality to be sex biased but not age biased. We suggest that these contrasting results may in part be explained by the lack of baseline data about the demographic structure of surveyed populations in previous studies. Our results stress the importance of baseline data for inferring demographic consequences of wind turbine collision mortality.

Plasma protein fractions in free-living white-tailed eagle (Haliaeetus albicilla) nestlings from Norway

BackgroundCapillary electrophoresis of plasma proteins has shown great potential as a complementary diagnostic tool for avian species. However, reference intervals for plasma proteins are sparse or lacking for several free-living avian species. The current study reports electrophoretic patterns and concentrations of plasma proteins determined for 70 free-living white-tailed eagle (Haliaeetus albicilla) nestlings from two locations in Norway (Steigen and Smøla) in order to establish reference values for this subpopulation using capillary electrophoresis. The nestlings were between 44 and 87 days of age, and the plasma protein concentrations were investigated for age, sex, year (2015 and 2016) and location differences. To our knowledge, this is the first report of reference intervals of plasma proteins analysed by capillary electrophoresis in free-living white-tailed eagle nestlings.ResultsThe plasma protein concentrations (% of total protein, mean ± SE) were determined for prealbumin (13.7%, 4.34 ± 0.15 g/L), albumin (46.7%, 14.81 ± 0.24 g/L), α1-globulin (2.4%, 0.74 ± 0.03 g/L), α2-globulin (11.7%, 3.72 ± 0.06 g/L), β-globulin (15.9%, 5.06 ± 0.08 g/L) and γ-globulin (9.6%, 3.05 ± 0.09 g/L). Significant differences were found between the two locations for prealbumin, α2- and γ-globulins. No significant differences were found between the two sampling years or sexes, and no effect of age was found for any of the plasma proteins. However, prealbumin levels were several folds higher than previously reported from adults of closely related birds of prey species. There were no other studies on capillary electrophoresis of nestling plasma available for comparison.ConclusionSignificant differences were found between sampling locations for prealbumin, α2- and γ-globulins, which may indicate differences in inflammatory or infectious status between nestlings at the two locations. Sampling year, sex or age had no significant effect on the plasma protein concentrations. These results provide novel data on plasma protein concentrations by capillary electrophoresis and may be useful for evaluation of health status in free-living white-tailed eagle nestlings.

THE ROLE OF SPECIAL PROTECTED AREAS OF THE MURMANSK PART OF THE GREEN BELT OF FENNOSCANDIA IN THE DIVERSITY CONSERVATION OF RARE BIRD SPECIES

The contribution of the existing and planned protected areas of the Murmansk part of the Green Belt of Fennoscandia to the conservation of the populations of bird species listed in the Red Data Books of the Russian Federation and the Murmansk Region is analyzed. The history of studies of the avifauna of each protected area is considered. The areas best studied by ornithologists (Ainovy Islands of Kandalakshsky Strict Nature Reserve (zapovednik), Pasvik Strict Nature Reserve, Kaita Regional Nature Reserve (zakaznik), planned zakazniks - Pazovsky and Vuorjema) and the least studied ones (Laplandsky Les, Kutsa regional zakaznik, planned Ionn-N'yugoajv, Spruce Forests of Alla-Akkajarvi zaka-zniks. and others) have been identified. The avifauna of the study area totals 256 species, including 35 red-listed species. It is demonstrated that the protected areas do preserve a high biodiversity of birds and maintain their populations. The best performance is observed for the Whooper Swan Cygnus cygnus, Smew Mergellus albellus, White-tailed Sea Eagle Haliaeetus albicilla, Kestrel Falco tinnunculus, Common Crane Grus grus, Dipper Cinclus cinclus and Great Gray Shrike Lanius excubitor. However, for some protected areas of regional status, knowledge gaps need to be filled through implementation of special biodiversity monitoring programs, research on the state of habitats of rare bird species, and assessment of their numbers.

No adverse effects on Lesser Spotted Eagle breeding in an area of high White-tailed Eagle density

Mesopredators frequently suffer lethal and/or non-lethal negative effects when breeding in sympatry with more powerful apex predators. The recent recovery of the White-tailed Eagle Haliaeetus albicilla (WTE) population throughout its range indicates the return of the largest predator of the raptor communities there. In this study, we assess the importance of habitat overlap and spatial distribution to the reproduction of the Lesser Spotted Eagle Clanga pomarina (LSE), a species that breeds sympatrically in areas of high WTE density near the Baltic Sea, but is three times smaller than the latter. Fewer water bodies surround the nesting sites of the LSE, and it uses agricultural areas and transitional habitats more frequently than the WTE. The same breeding territories are faithfully occupied by the LSE annually, irrespective of the distance between these and those of the WTE. We found that the breeding success of the LSE was not affected by the proximity or breeding output of the nearest pair of WTEs, nor was this affected by the number of WTE pairs present within a 3-km radius of nests. Our data suggest that the smaller LSE coexists with an abundant top predator without any obvious adverse effects on its population dynamics.

Allelic diversity and selection at the MHC class I and class II in a bottlenecked bird of prey, the White-tailed Eagle

BackgroundGenes of the Major Histocompatibility Complex (MHC) are essential for adaptive immune response in vertebrates, as they encode receptors that recognize peptides derived from the processing of intracellular (MHC class I) and extracellular (MHC class II) pathogens. High MHC diversity in natural populations is primarily generated and maintained by pathogen-mediated diversifying and balancing selection. It is, however, debated whether selection at the MHC can counterbalance the effects of drift in bottlenecked populations. The aim of this study was to assess allelic diversity of MHC genes in a recently bottlenecked bird of prey, the White-tailed Eagle Haliaeetus albicilla, as well as to compare mechanisms that shaped the evolution of MHC class I and class II in this species.ResultsWe showed that significant levels of MHC diversity were retained in the core Central European (Polish) population of White-tailed Eagles. Ten MHC class I and 17 MHC class II alleles were recovered in total and individual birds showed high average MHC diversity (3.80 and 6.48 MHC class I and class II alleles per individual, respectively). Distribution of alleles within individuals provided evidence for the presence of at least three class I and five class II loci the White-tailed Eagle, which suggests recent duplication events. MHC class II showed greater sequence polymorphism than MHC class I and there was much stronger signature of diversifying selection acting on MHC class II than class I. Phylogenetic analysis provided evidence for trans-species similarity of class II, but not class I, sequences, which is likely consistent with stronger balancing selection at MHC class II.ConclusionsRelatively high MHC diversity retained in the White-tailed Eagles from northern Poland reinforces high conservation value of local eagle populations. At the same time, our study is the first to demonstrate contrasting patterns of allelic diversity and selection at MHC class I and class II in an accipitrid species, supporting the hypothesis that different mechanisms can shape evolutionary trajectories of MHC class I and class II genes.

Diurnal birds of prey of national nature park ‘Dvorichanskyi’ and adjacent territories

The studies of species composition and abundance of diurnal birds of prey may be quite indicative of the state of natural ecosystems and of the level of impact of human-induced factors on their functions. Such studies are particularly important within the protected areas taking into account unfavourable conservation status of many species of the group. The status, abundance, aspects of habitat distribution and breeding habitat preferences of diurnal birds of prey were studied within national nature park ‘Dvorichanskyi’ and adjacent territories (750 sq. km, Dvorichanskyi district, Kharkiv Region, Ukraine) in 2010–2018. 22 species were registered. The breeding of six species was confirmed e.g. Black Kite (Milvus migrans), Marsh Harrier (Circus aeruginosus), Goshawk (Accipiter gentilis), Sparrowhawk (Accipiter nisus), Common Buzzard (Buteo buteo), Booted Eagle (Hieraaetus pennatus). The breeding of four more species is considered probable namely Honey Buzzard (Pernis apivorus), Montagu’s Harrier (Circus pygargus), White-tailed Eagle (Haliaeetus albicilla) and Hobby (Falco subbuteo). There are indications of possible breeding of Short-toed Eagle (Circaetus gallicus) and Kestrel (Falco tinnunculus). The rest of the species are migrating and/or wintering. The most numerous breeding species is Common Buzzard. The abundance of Booted Eagle is comparatively high that discerns the study area from other parts of Kharkiv Region. 40 nests of birds of prey were carefully inspected. The majority were found in ravine steppe forests (83%). Oak, alder and willow flood-plain forests are very important breeding habitats for Black Kite and Booted Eagle while ravine steppe forests are those for Goshawk, Sparrowhawk, Common Buzzard and Booted Eagle. Pedunculate oak (Quercus robur) is the most favourable tree species for building the nests (47.5% of all inspected nests) followed by European ash (Fraxinus excelsior) (15%) and European pear (Pyrus communis) (10%).

Complete mitogenomes of two Accipitridae, Haliaeetus albicilla, and Pernis ptilorhynchus

We performed high-throughput sequencing on the complete mitogenomes of two raptors, white-tailed eagle (Haliaeetus albicilla) and oriental honey buzzard (Pernis ptilorhynchus). This is the first time that the complete mitogenomes from Accipitridae subfamies, Haliaeetinae, and Perninae have been sequenced. Respectively, H. albicilla and P. ptilorhynchus mitogenomes were 17,719 and 17,927 bp base pairs long. The ND3 gene in both raptors possessed an insertion mutation, whereas only P. ptilorhynchus ND6 had two mutations. Our results benefit future raptor research through expanding the mitogenome database.

Sex‐specific patterns of reproductive senescence in a long‐lived reintroduced raptor

For many species, there is evidence that breeding performance changes as an individual ages. In iteroparous species, breeding performance often increases through early life and is expected to level out or even decline (senesce) later in life. An individual's sex and conditions experienced in early life may also affect breeding performance and how this changes with age. Long-term monitoring of individuals from reintroduced populations can provide unique opportunities to explore age-related trends in breeding performance that might otherwise be logistically challenging. We used a unique dataset from a reintroduced population of white-tailed eagles Haliaeetus albicilla in Scotland, which has been intensively monitored since their initial reintroduction in 1975, to study age- and sex-specific trends in two measures of breeding performance. This monitoring provided data on the breeding performance of known individuals ranging in age from 3 to 26years. We also explored changes in breeding performance in relation to early life experience (i.e., whether they were released or fledged in the wild). Breeding performance increased with age in early life in a similar manner for both sexes. We found stronger evidence for senescence in breeding performance in males than females. However, late-life female breeding success was associated with early life experience, while male senescent trends were not apparently impacted by conditions experienced during early life. Sexual differences in senescence mean that older males are less likely to breed successfully compared to older females, and this may influence females' mate changes later in life. This difference may suggest a linked sexual difference in survival rates or the possibility of proactive partner change by females in later life in this typically monogamous biparental species.

Monitoring contaminants, emerging infectious diseases and environmental change with raptors, and links to human health

ABSTRACTCapsule: Raptor research and monitoring informs issues of relevance to human health, including environmental contamination, emerging infectious diseases and environmental change.Aims: The paper examines the relevance of raptor research and monitoring to inform issues of relevance to human health, including environmental contamination, emerging vector-borne diseases and environmental change.Methods: Reviews of European Union policy context and role of raptor research and monitoring in detection of and response to contaminants. Examples include lead ammunition in White-tailed Sea Eagles Haliaeetus albicilla in Europe, and impacts of diclofenac on Gyps vultures in the Indian subcontinent. Comments on the relevance of raptor research and monitoring to emerging infectious diseases and environmental change, and considers the links between raptors and humans.Results: Biomonitoring of contaminants in raptors can perform useful purposes in relation to chemicals legislation. Raptors are useful sentinels of exposure to and effects of chemicals in the environment. Raptor research and monitoring can also elucidate environmental change and spread of emerging infectious diseases. Raptors are linked to humans through social, cultural and economic values.Conclusion: Raptors can be used to provide information relevant to human health and well-being. There are a number of challenges and opportunities in relating raptor research and monitoring to human health. Several areas with potential for development are outlined. The COST Action ‘European Raptor Biomonitoring Facility’ and the forthcoming LIFE APEX project will take forward relevant work.

The white-tailed eagle (Haliaeetus albicilla) in the Netherlands: changing landscapes, changing attitudes

In 2006, after centuries of absence, a pair of white-tailed eagles (Haliaeetus albicilla) bred successfully in the Netherlands. Since then, the species has slowly spread across the country. The white-tailed eagle’s return is a consequence of its spectacular increase in Northern Europe and Germany, and the westward expansion of the breeding area. At least one bird of the first breeding pair hatched in Schleswig-Holstein, Northern Germany.

Flock-fishing deep-diving piscivores (Great Crested Grebe Podiceps cristatus, Great Cormorant Phalacrocorax carbo, Common Merganser Mergus merganser) at Lake Vombsjön, southern Sweden, and those that exploit them

Lake Vombsjön in southern Sweden is visited by large numbers of Great Crested Grebes Podiceps cristatus (&gt;2000), Great Cormorants Phalacrocorax carbo (sometimes &gt;1000) and Common Mergansers Mergus merganser (up to 2000) in late autumn and early winter. Different species exploit them. Great Crested Grebes are used especially by commensal Common Gulls Larus canus; the gulls take advantage of fish that flee towards the surface. Common Gulls also use cormorants and mergansers in the same way but also try to kleptoparasitize them. Both Herring Gulls Larus argentatus and Great Black-backed Gulls Larus marinus kleptoparasitize these two species, while Red Kites Milvus milvus, Grey Herons Ardea cinerea and Carrion Crows Corvus corone use them commensally. White-tailed Eagles Haliaeetus albicilla seem to use both methods to obtain fish. On 50% of one hundred visits during November to March, eagles were seen flying low over the fishing flocks. They would fly a metre or so above the flocks and then accelerate and attack a bird holding a fish. The bird would then either try to escape by a rush or by diving, dropping the fish which the eagle seized. Interestingly, the flock-fishing birds showed no fear reactions towards the eagles but appeared to regard them similarly to large gulls.

A refinement of the Band spreadsheet for wind turbine collision risk allowing for oblique entry

A new spreadsheet is presented, to be used as part of the Band model for estimating potential avian mortality due to wind turbine strike. The spreadsheet extends the Band collision risk spreadsheet by allowing for oblique approach angles and wind speed. The differences in the results between this new spreadsheet and the standard Band spreadsheet are given for two species, the white-tailed eagle Haliaeetus albicilla and the South Island pied oystercatcher Haematopus finschi, chosen for their contrasting sizes and flight characteristics. Under more representative conditions, the true risk for large birds is shown to be substantially greater than that calculated by the Band spreadsheet. Examples of how to use the new spreadsheet with bird survey and wind data are given.

Settlement, habitat preference, reproduction, and genetic diversity in recovering the white-tailed eagle Haliaeetus albicilla population

The recovering population of white-tailed eagles Haliaeetus albicilla was studied in Lithuania, Central Europe. In the present study, we focused on (1) clarifying which theoretical distribution model better fits and describes the observed pattern of eagle settlement, (2) examining habitat preference at the level of nesting territory and its relationship with reproduction, (3) ascertaining the genetic diversity profile of the population using D-loop mtDNA. Between 1985 and 2011, the white-tailed eagle population recovered from 0 to 120 pairs and by the end of the period occupied a range of 34,000 km2. As indicated by a mean annual breeding success of 0.67, productivity 1.15, and brood size 1.73, the population reproduced well. The pattern of habitat settlement during the period of population expansion was not random as high-quality habitats were occupied first. Supporting the ideal free distribution model, reproduction was similar across nesting territories in three different habitat types, as well as between territories established in different years. The eagles preferred aquatic habitats, but these preferences were not adaptive in terms of breeding performance. Increased brood failures in later years possibly indicated the growing effect of density-dependent regulation. In total, six different haplotypes were identified in the sample of 45 individual birds. Haplotype diversity was 0.711. Phylogenetically, the Lithuanian population is most closely related to the populations of Sweden, Poland, and Germany, while similarity with Lapland, Kola, and Estonian populations was evident too. These findings indicate possible source populations directly or indirectly participating in the process of recovery of the formerly extinct Lithuanian population. Haplotypes distribution across the three habitat types in Lithuania was uneven.

Lead exposure and food processing in white-tailed eagles and other scavengers: an experimental approach to simulate lead uptake at shot mammalian carcasses

A serious hazard for avian scavengers is lead poisoning caused by feeding on shot mammalian carcasses containing fragments of lead-based bullets. Both obligate and facultative scavenging species are affected, such as the white-tailed eagle Haliaeetus albicilla for which lead intoxication is a major source of mortality. However, the exploitation of hunter-killed carrion by facultative avian scavenger communities is little studied. As bullet fragments recovered from the intestinal tract of white-tailed eagles were generally small and did not represent the full spectrum of available bullet fragment sizes, the hypothesis arose that this is the result of selective food processing in that eagles avoid the intake of large metal particles. Here, we used an experimental approach to identify lead-exposed species and explore the food processing of white-tailed eagles and other scavengers. We conducted feeding experiments with free-ranging scavengers in six eagle home ranges in northeastern Germany and with six eagles temporarily held in captivity. We provided ungulate carcasses containing non-toxic iron particles of different diameters, simulating bullet fragments, as food source. Primarily, avian scavengers such as ravens, eagles and buzzards exploited the carcasses, indicating them to be exposed to lead fragments and poisoning. With increasing diameter of experimental particles, free-ranging scavengers and captive eagles increased the percentage of particles avoided during feeding. Scavengers almost completely avoided fragments of 8.8 mm diameter. Behavioural observations of captive eagles showed that they detected iron particles predominantly by touching the experimental carcass with their bill tip, suggesting that they use mechanoreceptors to judge food quality. Our findings indicate that the use of bullets that deform or fragment into particles greater than 9 mm in size, such as numerous lead-free bullets, may prevent metal ingestion and poisoning in avian scavengers.

Sit-and-wait for large prey: foraging strategy and prey choice of White-tailed Eagles

Little is known about foraging strategy and prey choice in large raptor species and how they might change with age and season. Here, we present results about time allocation, foraging pattern and diet selection of adult territorial White-tailed Eagles Haliaeetus albicilla from northeastern Germany. To assess age-related differences, we also observed foraging behaviour in roaming juveniles. Eagles allocated most of their diurnal time to perching. Since perch-hunting was more efficient than flight-hunting, “sit-and-wait” for prey seems to be a low-cost, highly profitable foraging mode in eagles. A linear mixed model revealed that season significantly affected eagle foraging patterns. Success in prey capture decreased and duration of foraging flights increased considerably in winter. Eagle strike success varied significantly between different territories and increased with increasing habitat quality. Adults foraged more efficiently than juveniles, presumably because of their superior spatial knowledge and hunting skills. A use–availability design for prey selectivity indices judged by log-likelihood chi-square statistics indicated that eagles make choices, within both their primary prey fish and alternative prey waterfowl, consistent with predictions of optimality models. When prey was abundant, eagles preferred large over small fish and slow over agile waterfowl species. Thus, prey choice by eagles reflected a complex function of absolute availability, size and anti-predator behaviour of their prey. Our study demonstrates that large raptors such as White-tailed Eagles are generally energy maximisers and pursue a “sit-and-wait” hunting mode to capture profitable prey, and can modify their foraging strategy to cope with variations in weather conditions and food availability.

The first comprehensive estimate of the winter population of the White-tailed Eagle Haliaeetus albicilla along the Danube/ Prva celostna ocena zimske populacije belorepca Haliaeetus albicilla vzdolž Donave

Abstract In January 2014, the first ever comprehensive winter census of the Whitetailed Eagle Haliaeetus albicilla along the Danube River was conducted, using mostly point and transect counts. Altogether, 550-700 eagles were counted. The upper range of the estimate may in fact be more realistic because 615 km of the Danube were not surveyed. Birds were observed in every country along the Danube. Hotspots of occurrences were (1) the Central Danube floodplains - the area encompassing the lower Hungarian section (Danube- Drava National Park), Kopački rit Nature Park (Croatia), and the Gornje Podunavlje Special Nature Reserve (Serbia); and (2) the Danube Delta Biosphere Reserve. According to the Action Plan for the conservation of the White-tailed Eagle along the Danube, future winter counts should be made regularly, and lower variation in the resulting eagle numbers achieved by a higher degree of synchronization between individual countries. This study reinforces the importance of protected areas along the Danube as a backbone for the conservation of White-tailed Eagles and biodiversity.

Contrasting population trends at seabirds colonies: is food limitation a factor in Norway?

Norwegian Northern Gannet Morus bassanus populations exhibit contrasting trends on a regional scale, with several colony extinctions having occurred in recent decades. In an attempt to understand the ecological drivers of such variability, we tested whether resource availability is a factor limiting the current development of gannetries in the Lofoten/Vesteralen area. Between 2007 and 2010, we recorded arrival and departure times of breeding Northern Gannets from two colonies from regions showing contrasting population growth rates during the past two decades. We also recorded the duration of joint attendances by Northern Gannet parents at the nest, performed opportunistic diet sampling and counted numbers of occupied nests. Finally, we compiled ring recoveries over a 30-year period to assess inter-colony movements. Norwegian Gannet parents spent more time together, attending their chick, and performed shorter foraging trips than those in British and French colonies of similar size. This suggests that, despite some annual variations, their foraging effort was relatively low. Diet samples from both colonies mainly constituted fish of high energetic value, such as large herring Clupea harengus, mackerel Scomber scombrus, and saithe Pollachius virens, prey that are relatively abundant within the study area. Data from ringed birds revealed a northward movement of adults ringed as breeding birds and chicks from extinct Lofoten colonies that established a growing colony close to the North Cape. Recorded foraging features (trip duration, joint attendance and prey quality) during our study does not indicate food availability as a limiting factor explaining successive extinctions and re-colonisations of breeding sites in Lofoten/Vesteralen. White-tailed Eagles Haliaeetus albicilla are known to predate opportunistically on Northern Gannet adults or chicks and their populations are growing in the Lofoten area. Their potential impact on the Norwegian Northern Gannet population dynamics should be further investigated.