Thai National Parks

Birds of Thailand

Species of Thailand

White-tailed eagle

In Thai: นกอินทรีหางขาว, nok in-sree hang khao

Binomial name: Haliaeetus albicilla, Carolus Linnaeus, 1758

The white-tailed eagle (Haliaeetus albicilla) is a very large species of sea eagle widely distributed across temperate Eurasia. As are all eagles, it is a member of the family Accipitridae (or accipitrids) which includes other diurnal raptors such as hawks, kites, and harriers. One of up to eleven members in the genus Haliaeetus, which are commonly called sea eagles, it is also referred to as the white-tailed sea-eagle. Sometimes, it is known as the ern or erne (depending on spelling by sources), gray sea eagle and Eurasian sea eagle

While found across a very wide range, today breeding as far west as Greenland and Iceland across to as far east in Hokkaido, Japan, they are often scarce and very spottily distributed as a nesting species, mainly due to human activities. These have included habitat alterations and destruction of wetlands, about a hundred years of systematic persecution by humans (from the early 1800s to around World War II) followed by inadvertent poisonings and epidemics of nesting failures due to various manmade chemical pesticides and organic compounds, which have threatened eagles since roughly the 1950s and continue to be a potential concern. Due to this, the white-tailed eagle was considered endangered or extinct in several countries. However, some populations have recovered well due to some governmental protections and dedicated conservationists and naturalists protecting habitats and nesting sites and partially regulating poaching and pesticide usage, as well as careful reintroductions into parts of their former range.

White-tailed eagles usually live most of the year near large bodies of open water, including both coastal saltwater areas and inland freshwater, and require an abundant food supply and old-growth trees or ample sea cliffs for nesting. They are considered a close cousin of the bald eagle (Haliaeetus leucocephalus), which occupies a similar niche in North America.

Taxonomy

The first formal description of the white-tailed eagle was by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae under the binomial name Falco albicilla. The genus Haliaeetus was introduced in 1809 by the French naturalist Marie Jules César Savigny in the Description de l'Égypte. The name Haliaeetus is New Latin for "sea-eagle", from Ancient Greek hali-, "sea-" and aetos, "eagle". The specific albicilla, "white-tailed", is from New Latin albi-, "white" and cilla, "tail". The Anglo-Saxon name erne means “soarer”. It has many Gaelic names, including iolar sùil na grèine or 'eagle of the sun's eye.'

Systematics

The white-tailed eagle is a member of the genus Haliaeetus, a monophylic group comprised by 11 living species, including the closely related Ichthyophaga fish eagles which may or may not be part of a separate genus. The latter group, comprised by the lesser (Haliaeetus humilis) and the grey-headed fish eagle (Haliaeetus ichthyaetus), differ mostly in life history, being more fully devoted to fish eating and habituating wooded areas, especially in mountainous areas. In appearance the two Ichthyaetus are slenderer, longer tailed and more uniform and grey in colour than typical sea eagles. This species pair may not be genetically distinct enough to warrant division into separate genera. Other than these Ichthyophaga-type species found farther north in Asia, Sanford's sea eagle (Haliaeetus sanfordi) of the Solomon Islands is the most atypical Haliaeetus, retaining rufous-brown plumage into adulthood (this particularly resembling the white-bellied sea eagle juvenile, likely a closely related species) more typical of juveniles in other species and it also dwells more so in dense, coastal forests where it feeds mostly on birds and mammals rather than fish and water birds. Outside of the genus Haliaeetus, among other extant forms, they appear to be most closely related to milvine kites and Old World vultures, based on modern forms from these subfamilies that broadly share morphological and life history traits with sea eagles: the Brahminy kite (Haliastur indus) (historically sometimes referred to as the “red-backed sea eagle”) and the palm-nut vulture (Gypohierax angolensis) (which was once widely referred to as the “vulturine fish eagle”). The relation of these species to the sea eagles is partially borne out by their genetic sequencing. Other groups, beyond milvine kites and Old World vulture, of modern accipitrid that are seemingly in some way related, albeit very distantly, to the sea eagles include Accipiters, harriers, chanting-goshawks and buteonines. Notably excluded from their relations are most other species referred to as “eagles”, including booted eagles and snake and serpent eagles.

The white-tailed eagle itself forms a species pair with the bald eagle. These diverged from other sea eagles at the beginning of the early Miocene (c. 10 mya) at the latest, possibly (if the most ancient fossil record is correctly assigned to this genus) as early as the early or middle Oligocene, about 28 mya. A recent genetic study of mitochondrial DNA is consistent with this idea. Greenlandic white-tailed eagles (proposed as H. a. groenlandicus) form, on evolutionary time scales, a relatively recently founded population that has not yet accumulated many unique genetic characteristics and may not strictly fulfill the distinction of a subspecies. However, the population appears to be demographically isolated and deserves special protection. At one time an eastern subspecies (H. a. brooksi) was proposed as well but there is little evidence supporting this as more than a case of clinal variation in coloring and size (i.e. the eastern average slightly darker and smaller than more westerly ones). As in other sea-eagle species pairs, this one consists of a white-headed (the bald eagle) and a tan-headed species. They probably diverged in the North Pacific, spreading westwards into Eurasia and eastwards into North America. Like the third large northern species, Steller's sea eagle (Haliaeetus pelagicus), adults have yellow feet, beaks and eyes. Another species, likely intermediate between the white-tailed, bald and Steller's sea eagles and the Ichthyophaga type fish eagles, is the Pallas's fish eagle, which in life history seems to range farther from water and to higher elevations than the three northern species normally do. Due to the similar dietary and nesting habits of sea eagles, they are mostly allopatric in distribution as competition can be considerable between these eagles.

Currently, eagles only occur in the Hawaiian Islands as vagrants, but Quaternary bones of Haliaeetus have been found on three of the major islands. An ancient DNA study published in 2015 characterized the rapidly evolving mitochondrial control region of one of these specimens. DNA from a ∼3500-year-old sea eagle skeleton found in a lava cave on Maui was sequenced. Phylogenetic analyses suggested that the Hawaiian eagle represents a distinct (>3% divergent) mtDNA lineage that is most closely related to extant white-tailed eagles. Based on fossil calibration, the Hawaiian mtDNA lineage probably diverged around the Middle Pleistocene. Thus, although not clearly differentiated in morphology from its relatives, the Hawaiian eagle likely represented an isolated, resident population in the Hawaiian archipelago for more than 100, 000 years, where it was the largest terrestrial predator. The reasons for its extinction are unknown.

Size

The white-tailed eagle is a very large bird and one of the largest living birds of prey. It is the largest of the dozen species called eagle to be found in Europe and is the largest eagle across its distribution, excluding the Russian Far East and during winter in Hokkaido where it co-exists with its larger cousin, Steller's sea eagle. The white-tailed eagle is sometimes considered the fourth largest eagle in the world and is on average the fourth heaviest eagle in the world. The only extant eagle species known to be more massive in mean bulk are Steller's sea eagle, the harpy eagle (Harpia harpyja) and the Philippine eagle (Pithecophaga jefferyi). The white-tailed eagle measures anywhere from 66 to 94 cm in total length with a typical wingspan of 1.78 to 2.45 m ftin. This species may have the largest wingspan of any living eagle. The Steller's sea eagle, which is larger in weight, total length and non-wing standard measurements, may be the closest rival for median wingspan amongst living eagles. Average wingspans are not known for the Steller's species, however white-tailed eagles do appear to outsize the average wingspan of the wedge-tailed eagle (Aquila audax), which is sometimes also titled the largest winged extant eagle (however one wedge-tail did possess the largest wingspan ever verified for an extant eagle). In one sample from Norway, 5 male white-tailed eagle were found to average 2.26 m ftin and 8 females were found to average 2.37 m ftin. In another sample of wild birds of unspecified origin, 5 males were found to average 2.1 m ftin and 7 females averaged 2.3 m ftin. Record wingspans have included a specimen from Greenland which measured 2.53 m ftin while another specimen apparently spanned 2.6 m ftin. The bald eagle broadly overlaps in size with the white-tailed eagle. In direct comparison, the white-tailed eagle averages somewhat larger in body mass than the bald eagle and may be marginally larger in bill and talon size although these linear aspect can be quite similar between the two species. However, the white-tailed has a significantly larger wing chord and average wingspan. On the other hand, the bald eagle usually possesses a longer tail length on average, which imparts a somewhat longer total length that the white-tailed eagle, and a longer mean tarsal length.

Size variation is generally a clinal trend, these figures usually being measured in standard measurement such as wing, tail and tarsal length, or body mass rather than wingspan or total length. As expected for many widely distributed animals of varied lineages, the white-tailed eagle conforms to Bergmann's rule in that more northerly birds tend to outsize those found relatively closer to the Equator. Somewhat less predictably, size seems to decrease from west to the east as well. The largest white-tailed eagles appear to be found in Greenland, which are just slightly larger than those from Scotland and Scandinavia and notably larger than eagles from central Europe, especially in proportions of the wing area. Meanwhile, those from the southerly portions of their breeding range, such as Asia Minor (principally Turkey), southern Kazakhstan and Korea Bay appear to be the smallest-bodied population, but this is complicated by the fact that there's nearly been no comprehensive measurements or published weights known for these extremely sporadic and rare Asian populations of eagle. Furthermore, weights of fully grown eagles from Greenland are not known. Unlike many accipitrids, in white-tailed eagle (and seemingly other sea eagles as well) juveniles are often of similar weight to adult eagles, whereas in most the juveniles will usually weigh somewhat less. However, more typically, juvenile eagles have somewhat larger average wing and tail lengths than adults. In the white-tailed eagle, body mass can typically range from 4 to 6.9 kg in females. The slightly smaller male may typically weigh from 3.1 to 5.4 kg. Average weights in European white-tailed eagles can range from 4.02 kg in 5 males and 5.11 kg in 9 females to (from the reintroduced birds of Scotland of Norwegian stock) 4.98 kg in 39 males and 6.06 kg in 43 females. In comparison, the weight ranges for white-tailed eagles from northeast China were claimed as only 2.8 to 3.78 kg in males and 3.75 to 4.6 kg in females. The heaviest female white-tailed eagles can apparently scale up to 7.5 - 8 kg and even males can sometimes weigh up to 6.5 kg, which would make the largest males perhaps the heaviest recorded modern male eagle as male harpy and Philippine eagles (being more sexual dimorphic in favor of the female) are not known to exceed 5 kg (the highest weights for male Steller's sea eagle are not known). The global mean body mass of white-tailed eagles is estimated at approximately 5 kg. The average female Steller's sea eagle may weigh just under 25% more than the average female white-tailed eagle (the average weight of male Steller's is not known) while the average European golden eagle weigh about 11-12% less than the average European white-tailed eagle and the bald eagle species as a whole about 10% less than the white-tailed eagle species.

Standard measurements and sexual dimorphism

The most reliable method to sex birds is by tarsus width and depth and bill depth but these are infrequently measured. In some cases females are as much as 25% heavier and 15% greater in linear dimensions, though the sexes are rarely this discrepant in standard measurements. Among standard measurements, the wing chord is 552 to 695 mm in males, averaging 606 and 645 mm in European adults and juveniles, respectively, and 646.5 mm in Greenland males. In females, the wing chord may measure 605 to 740 mm, averaging 668 and 685 mm in European adults and juveniles, respectively, and 691.3 mm in Greenland females. Adult tail length is 250 to 331 mm in males, averaging 280 mm, and 276 to 330 mm in females, averaging 305 mm. Juvenile tail lengths can reach roughly 380 mm in both sexes, however. The tarsus is 90 to 101 mm, averaging 95.5 mm. In terms of their killing apparatuses, their hallux claw, the largest talon on all accipitrids, is 37 to 46 mm in length, averaging 40.9 mm. The hallux claw averages about a centimeter less than that of a golden eagle and is more sharply curved, an adaptation to prevent escape of slippery prey such as fish, while that of a bald eagle is similarly about 40.4 mm and of similar curvature. The exposed culmen is typically large as in all Haliaeetus, ranging from 45 to 65 mm, with an average of 56.1 mm. The average culmen length of the bald eagle is 54.3 mm, thus averaging slightly smaller. However, the average culmen length in the large bald eagles of Alaska is considerably larger than other bald eagles as well as most white-tailed eagles at up to 75 mm and can even rival the length (but perhaps not the girth) of the truly massive bill of the Steller's sea eagle.

Coloring and field appearance

The adult white-tailed eagle is a greyish mid-brown color overall. The plumage is fairly uniform over most of the body and the wing but the upper wing coverts are typically somewhat paler. Contrasting with the rest of the plumage in the adult are a clearly paler looking head, neck and upper breast which is most often a buffy hue. In worn or bleached plumages these light areas can be even paler at times, ranging to nearly whitish, which can render a resemblance in such eagles to a washed-out bald eagle. Some of the palest birds are also washed out looking even on the body which can appear anywhere from cream-tawny to light grayish. It is thought that in some populations perhaps paleness increases with age, although it is possible that there is an historic genetic factor to such pale variations. On the contrary, some adults can also be a richer, more deeply dark brown (or somewhat rufescent) than average with perhaps a mild increase in average darkness of hue to the east of the species’ range. When many of the feathers are freshly molted, they can take on a slight purplish gloss. The brownish hue of the adult overall makes the somewhat wedge-shaped white tail stand out in contrast. All the bare parts of their body on adults are yellow in color, including the bill, cere, feet and eyes. Juvenile and immature are a much darker brown than the adult white-tailed eagle and are more unevenly marked, with whitish feather edgings variably showing, mostly manifesting in some small areas of the underside and under-wing, with a narrow white axillary strip usually apparent. Their upperside is usually similarly darkish brown but variable based on extent of blackish-brown tip to otherwise buff-brown feathers of the mantle, back and upper wing. The head of juveniles is normally a blackish-brown hue, somewhat darker and always more uniform than most other feathers. The juvenile white-tailed eagle's tail tends to be a washed out greyish-cream color with messy blackish color on the feather edges and on the tips. Some individual juveniles may evidence some faint barring on the tail while others may appear largely dirty whitish on the tail. The bill of juveniles is usually nearly half dark brown from the tip and half dirty, dull yellowish or gray to the base, while the feet are usually a dirty yellow and the eyes are a darkish brown. Juvenile males may average a slightly darker brown plumage with less speckling on their upper body than like-age females, their head and neck plumes may also appear shorter, which can accentuate the slighter, more angular skull possessed by males. In disposition, the male juveniles are said to be more highly strung and higher voiced than their female counterparts. The head gradually grows paler over several years. The whitish mottling may increase on the upperparts, belly and especially on the underwing area later into their 3rd year (considered the first subadult plumage) and subadult birds can appear fairly blotched with white but much individual variation in coloring is known at this age. However, this white mottling then fades late into the 4th year and the plumage becomes less contrasting. Although sexual maturity is considered to be attained at 5 to 6 years of age, usually the fully white tail and the uniform pale head and neck are not obtained until the 8th year. Juveniles first molt in May/June until October/November at just over a year of age. Their 2nd molt is the following year in March or April, with two more subsequent molts usually beginning around this time for the next couple years. Like other large raptors, feathers are molted at slow intervals in order to not inhibit food capture. Only relatively small portions of the flight feathers are molted each year. Molts occur more or less continuously, although it may pause in winter if food is in short supply.

White-tailed eagles are of all ages typically perch in quite upright positions on exposed branch, rock or other vantage point, but tend to sit more horizontally on the ground or other level surfaces. They have an ample bill with a relatively high culmen, helping impart a relatively narrow and high crowned facial look, especially compared to Aquila eagles. Their neck is at times unexceptedly long-looking, more so than the bald eagle, which can give the upper body a vulturine appearance. The tail is relatively short, in some adults it can appear almost strangely so in relation to the massive body, and slightly wedge-shaped. All ages have a well-feathered tibia but bare tarsi. In flight, the white-tailed eagle's wings are extremely broad and deeply fingered (usually at least 6 fingers tend to be visible), creating a "flying door" effect. Juvenile are longer tailed, which is usually more evident in flying than perched birds, with sometimes a slightly bulging section of feathers manifesting on the wing secondaries. The species tends to fly with shallow wing beats, at times their beats can be fairly fast for bird of this size interspersed at times with glides or not gliding at all. At a great distance, they may suggest a huge brown heron due to this flight style. The wings are held flat or slightly upraised at tip in flight and the species is well known to soar extensively. The white-tailed eagles can be surprisingly maneuverable on the wing, usually during aerial displays or dogfights with other birds. The eagles may too maneuver by half-closing both wings or closing one wing.

Vocalizations

The white-tailed eagle is considered a very vocal bird of prey during the breeding season, although some authors consider their voice "not loud or impressive for the size of the bird". The male call is oft transcribed as or , while the female is a deeper or . These will increase in tempo and pitch, with about 15-30 calls in a sequence. Often pairs will duet during early spring, in flight or from a perch. When perched, the male calls with the head thrown back and upwards in the last call ended with a lower ko-ko-ko, the perched call of females is similar but deeper, a . Typically, the perched version of their calls tend to be shriller and higher than those issued in flight. In courtship display, male calls answered by females with a lower . Young in nest call a shrilly , while the female when receiving food from male calls out with or . Single or repeated or similar component of calls used in other circumstances, but this can be very variable. Alarm calls tend to be 3-4 short, loud or notes. Sometimes a different call of alarm or anger, a deep or , similar to alarm calls of a large gull, is also uttered when a nest is approached (usually recorded while directed towards humans). The young let out a monotonous when hungry (or "bored") which intensifies if the eaglets are not fed or brooded immediately.

Identification

Given reasonable view, adult white-tailed eagles are difficult to mistake for any other bird. There are no other eagles with fully white tails in their range except for in the easternmost limits of their range, their cousins the bald and Steller's sea eagles, which in adults are obviously very different in all other respects of plumage. Even in poor light, the bald species shows a sharp demarcation from white to dark brown whereas the color contrast is far subtler in white-tailed eagles between their brown body (of a paler hue than that of a bald eagle) and buff-colored head. At a great distance, the adult may be potentially confusable with the Griffon vulture (Gys fulvus), as the coloring of the two species is vaguely similar and they can overlap somewhat in size although the vulture can average rather heavier and longer winged. However even at long range, the relatively tiny head, distinctly curved trailing wing-edges and more raised wings make the vulture distinctive from the white-tailed eagle. Juveniles may be harder to distinguish, mainly from other sea eagles in few areas of overlap. In northern Mongolia (perhaps spilling over into southern Siberia), the northern part of the Caspian Sea and some central and southern parts of Kazakhstan, the white-tailed eagle may (or may not) live alongside the rarer, relatively poorly-known Pallas's fish eagle. The Pallas's juveniles are more distinctively whitish marked on the underwing. In flight or perched, the Pallas's fish eagle are usually markedly smaller and slighter than white-tailed eagles with a longer and differently marked tail. At all ages, the white-tailed eagle averages a duller, slightly darker and browner colour overall than the Pallas's fish eagle. Pallas's fish eagles are mid-brown on the body in juvenile plumage with no paler feather edging as seen in juveniles and especially subadults of the larger species. Adult Pallas's fish eagles are immediately distinctive rufous hue with a more restricted but more sharply demarked paler buffy head. Bald eagle juveniles may be found together with white-tailed eagles in the Aleutian islands (where the white-tailed eagle formerly bred until about 30 years ago) and when vagrants of white-tails occur in Alaska. Juveniles of bald and white-tailed eagles often strongly resemble each other but the bald eagles have a shorter neck, a relatively longer and squarer tail, and somewhat less broad wings. In the coloring, the bald juvenile is similarly as dark or even darker brown above as white-tailed eagle juveniles but on the underside often has more extensive whitish mottling, especially on the underwing. Steller's sea eagles are usually distinctly larger and longer tailed, with a taller, bulkier look in eagles standing on the ground or perched. Steller's juveniles have a different wing shape (roughly paddle-shaped) and a considerably more massive and paler bill, which is yellow even in juveniles unlike in bald and white-tailed eagles. Juvenile Steller's sea eagles are a distinctly darker soot colour than juvenile white-tailed eagles with even less whitish showing on the body than the latter species but, on the other hand, the underwing often as white marked as juvenile bald eagles (dissimilarly from juvenile white-tailed eagles), albeit in different pattern. In all three large northern sea eagles, the tail color is similar at the various stages of development but the shape is more distinctive, especially the bolder wedge shape of the Steller's. The cinereous vulture (Aegypius monachus) may too be considered superficially similar to the juvenile white-tailed eagle, but it is considerably larger and longer-winged and possesses a more uniform and darker hue with conspicuous paler legs and a relatively smaller head. Young white-tailed eagles are also potentially confusable with any Aquila, but should be obvious even as a silhouette in its huge wings, relatively truncated and slightly wedge-shaped tail and obvious projection of the neck and head. All Aquila lack pale the axillary band often visible on juvenile and subadult white-tailed eagles. Some greater spotted eagles (Clanga clanga) can suggest the wing shape of a white-tailed eagle but are far smaller and shorter winged and never bear a protruding head. Similarly, the eastern imperial eagle (Aquila heliaca) may suggest a white-tailed eagle in its flat wing profile and relatively large head and neck but is also visibly smaller with far less broad wings and a relatively longer tail. Like all Clanga and Aquila, both greater spotted and eastern imperial eagles should be obviously distinct from white-tailed eagles by plumage characteristics. The golden eagle usually appears slightly smaller than the white-tailed eagle and tends to be more dashing in flight, which is usually done with a distinct dihedral. When perched, the golden eagle looks more sleek and compact than the rangier white-tailed eagle and tends to be a darker, richer hue of brown. Golden eagles have a much shorter neck, with a smaller head and bill and a longer, squarer tail. White wing patches of juveniles are also differently distributed in golden than juvenile white-tailed eagles.

Breeding range

This eagle breeds in northern Europe and northern Asia. Their range extends to as far west as southern Greenland (prevented from breeding further north due to the short summers), northern and eastern Iceland, and the reintroduced populations in some areas of England (introduced in 2019), Ireland and Scotland, particularly conserved coastal spots. In mainland Europe, often isolated outposts remain in coastal and western Norway (broadly), northern and southwestern Finland, eastern Sweden, southern Denmark (and some spots in the north), islands of the Baltic Sea, western Austria, northeastern Germany, northern and eastern Poland, the Czech Republic, much of the east Baltic countries, the non-montane areas of the Ukraine, eastern Slovenia, central and southern Hungary (and adjacent northeastern Croatia), very sporadically in Greece, the Danube sections of Romania and Bulgaria to the Black Sea and western and eastern Moldova. The bird returned to the Netherlands in 2006 and in 2018 the number of breeding pairs had increased to 14. In Asia Minor, it only remains as a breeder in very sparse and small pockets of Turkey and Georgia, taken as a region there is likely to be fewer than 30 breeding pairs in this region. In the Middle East, the white-tailed eagle may still be found breeding only along the southern coast of the Caspian Sea in northern Iran and southwestern Turkmenistan. Discontinuously, they are found as residents in Kazakhstan where they live in a long strip of the southern part of the country starting at the Aral Sea and the northwestern portion (but not, as far as is known, breeding in the Kazakh part of the Caspian Sea coast). The only country in which the white-tailed eagle is found over a continuous and extremely large area is Russia. The species is found very broadly everywhere in Russia from European Russia in the west to the Bering Sea in the east, only being fully absent as a nester as far as is known from the high Arctic regions and a section bordering westernmost Kazakhstan, although it breeds to south of this in the Russian coastal part of the Caspian Sea. Their northern limits occur in Russia to the Ob river to 70 degrees north at the mouth of the Yenisei River and on the Gyda and Yamal Peninsulas, to the Kolyma, Indigirka and Lena rivers to above 72 degrees north, even to 75 degrees north on the Taymyr Peninsula. They are said to be common around the White Sea, reportedly even the most abundant bird of prey locally and found both on coasts and inland lakes, although breeding rates are low due to the frigid weather. From Russia, breeding populations spill somewhat into northernmost Mongolia, extreme northwestern China and northern North Korea. The white-tailed eagle also breeds on Sakhalin Island, the Kuril Islands and Hokkaido, the northernmost island of Japan.

Wintering range

The wintering range is less well understood for the white-tailed eagle given the extreme reductions and fluctuations of northern breeding populations over the last few centuries, so that the delineation of regular wintering areas versus areas of mere vagrancy is difficult to ascertain. It is known that a small number winter on Etang de Lindre of Lorraine, France as well as an area on the border of France to Germany around Strasbourg, with vagrants to elsewhere in France, as well as to Spain, Portugal and Malta. A well-defined wintering population may occur in much of the Netherlands, even with infrequent modern breeding in the northern coastal areas. A non-breeding population is known in western Germany from North Rhine-Westphalia to Bonn, as well as far northern Germany into southwestern Denmark. Other established wintering areas are known in Europe in west-central Italy, northern Austria, fairly broadly in southern Slovakia and northern Hungary and a few protected pockets of Southeast Europe apart from the portions in the north and east where they still breed. Intermittent forms of vagrancy and migration (most from eagles that breed in or disperse from Russia) are known to occur in several areas of Turkey, the Levant countries, Azerbaijan and Iran down to even the Persian Gulf, albeit seldom is the species to be found commonly or reliably anywhere in these regions. Further east, rare wintering areas are known in a few small, scarce pockets of Turkmenistan, Afghanistan, Uzbekistan, Tajikistan and Pakistan. It is a very rare winter visitor to India, namely the extreme northwest and along the border of Nepal to Bhutan and extreme northern Bangladesh. Scattered pockets of wintering birds are known to occur too in central and southern China, into northeastern Myanmar, and more broadly and regularly in much of northeastern China. Good numbers winter too in much of South Korea and Japan down to as far as Honshu. White-tailed eagles dispersing from their breeding grounds or natal sites in the Russian Far East are known to occasionally disperse across the Bering Sea to North America in several parts of the Aleutian Islands, the Pribilof Islands and some of mainland coastal Alaska down to Kodiak Island. Some white-tailed eagles even bred in Alaska on Attu Island in the late 1970s to the early 1980s (until 1984 when the last attempts were recorded) but it was not clear whether young were ever successfully fledged.

Habitat

White-tailed eagles may be found in varied habitat but usually are closely associated with water and generally occurs in lowland areas. Although mainly a lowland species, the species is known to live at elevations of 1500 to 2300 m so long as there is water access in some parts of Central Asia and Siberia. In coastal areas, the species may range from high sea cliffs down to low-lying islands and archipelagos. Especially in winter, many white-tailed eagles often frequent low coastal spots, estuaries and coastal marshes. Several studies have supported that coastal areas are preferred when available during winter. In many areas, white-tailed eagles can seem to switch freely between usually cliff habitat and wooded spots for nesting sites and the center of their home range habitat. In some areas, such as Japan, this species may occur in regions with intensive human fishing activity and they may become unusually partially habituated to this human presence. Inland, white-tailed eagles usually require secluded woods, forested areas or groups of trees with tall mature trees and access to freshwater wetlands such as lakes, river systems, marshes or extensive, low-disturbance farmland. In the alluvial wetlands of Croatia, 95% of nests were found within 4 km of deep freshwater. In some areas, white-tailed eagles readily visit commercial fish farms, carp ponds and similar areas with easily accessible food but they will usually avoid areas where human disturbances (especially noisy varieties such as construction, water sporting and heavy boating activities and hunting) commonly occur. However, forestry activity and resulting lessened numbers of tall mature trees and large tree stands in Estonia was found to affect breeding white-tailed eagles less so than it seemed to affect breeding black storks (Ciconia nigra). On the other hand, from studying wintering white-tailed eagles in partially or heavily disturbed wetlands in parts of the Netherlands shows that such areas cannot support the eagles for any long-term period and may only be visited for a day or two by individual eagles.

Behaviour

White-tailed eagles spend much of their day perched on trees or crags, and may often not move for hours. Perhaps up to 90% of a day may be spent perched, especially if weather is poor. Also, they will alternate periods of soaring with perching, especially flying over water or well-watered areas, but do considerably less soaring on average than do golden eagles. Pairs regularly roost together, often near to their nest, either on a crag or tree or crevices, overhung ledges or small isolated trees on a crag.

Migration and dispersal

The white-tailed eagle may be considered a rather inconsistent and partial migrant. The species seldom migrates in the western part of its range, with eagles even breeding as far north as Greenland, Iceland and coastal Norway not moving at all for winter, but for some southward juvenile movements following dispersal. Juveniles overall are more migratory and dispersive and leave natal areas sooner, which is by August–September in northwestern Europe and return later, by March/April, than adults do. Few Norwegian juveniles, per banding studies, were recorded to travel any considerable distance. Extreme cases include one that was found 720 km south of its nest near Karlstad, Sweden, another set of 4 color marked 1st year juveniles were also recorded to turn up in southern Sweden but one was found down to the Wadden Sea in the Netherlands and it is likely that trickling down numbers of Norwegian post-dispersal juveniles have gone onto form much of the known Dutch white-tailed eagle population. In contrast, young from Finland and Sweden tend to distribute to the southwesterly direction to the shores of the Baltic sea. One from Finland was recovered 520 km west in northern Norway and another was found as far south as Bulgaria. In more southerly areas, winter movements are drawn-out and irregular, with most mature pairs probably never leaving their nesting haunts year-around. Those that breed on inland waterways may migrate to sea coast. German juveniles usually do not travel far, with most recorded to travel less than 50 km from their nests and a majority staying near the Baltic coast. However, some eagles that hatched from nests in Germany have been found as far south as in Italy, 1030 km away to the southeast, or to Gironde, France, 1520 km to the southwest. In several parts of Russia, quite unlike many European populations, the white-tailed eagle seems to be largely migratory. In the far east, the species appear to take different migratory routes in fall and spring, traveling from north-central Kamchatka thru the Kurile islands to Hokkaido in fall, while in spring these eagles travel north through Sakhalin and the Okhotsk Coast. In the White Sea area, southward moments begin in September with most white-tailed eagles being gone by November but in mild winters some adults may remain behind. Some white-tailed eagles from the White Sea were found well over 2000 km away to the west, in countries such as Hungary and Italy. Return spring migration to the White Sea is by February–March. During winter, whether long-distance migrants or short-distance dispersers, white-tailed eagles tend to become gregarious, especially younger juvenile birds. Many such groups can contain up to 10 and, in areas near large breeding populations such as in Norway, at least 30-40 individuals. Wintering congregations at the Baltic coast and on the River Elbe from 37 winters show that arrivals begin in November, with numbers peaking in January and then declining during March and early April. Although juveniles usually return to their natal area some apparently overshoot these areas, such as those returning to Romania or on the Black Sea which have been recorded 330 km north of their natal site and 510 km northeast of their natal site.

Territoriality

Territory size in white-tailed eagles may vary from 52 to 415 km2, usually less than 130 km2, per one estimate. However, home ranges in northeastern Germany were much smaller than this, at 2.25 to 19.16 km2. While territorial behavior is known in well more than half of all modern birds, essentially all predatory birds of different lineages are particularly strongly territorial because the live prey necessary to feed a family, including the female of the pair (which must remain near the young for them to survive) and the young themselves, tends to be sparser. Furthermore, appropriate habitat is needed in which to execute this hunting and also, of course, to build a nest with some security. While a relatively gregarious raptor, especially among wintering birds and juveniles and immature birds, they are territorial and intrusion by a male in adult plumage often provokes vigorously fighting, in which either combatant can even die. In some cases, these viscous fights can even cause damage to the nest as the two fighting eagles plummet down trying to slash at each other.

Dietary biology

The white-tailed eagle's diet is varied, opportunistic and seasonal. Prey specimens can often include fish, birds and, mostly in a secondary capacity, mammals. White-tailed eagles are powerful predators and capable of attacking large prey of considerable sizes but, like most predators, prefer prey that is vulnerable and easy for them to capture. Especially during the winter (and opportunistically in all seasons), many birds of the species live largely as scavengers, usually by coming across available carrion or watching for the activity of corvids, vultures or other raptors. White-tailed eagles in northeastern Germany were shown to hunt mostly from perches, in a “sit-and-wait” style, usually from a prominent tree perch. Like other sea eagles, they can only capture fish normally in the littoral zone, seldom hunting fish when they exceed a water depth of 1.5 to 2 m. In addition to trees, they may also use crags, hillocks or high grassy tussocks as hunting perches so long as the perch provides a good overall view of the environment. Fish tend to be grabbed in a shallow dive after a short distance flight from a perch, usually with the eagles only getting their feet wet. Occasionally, though, white-tailed eagles have been recorded plunging right into water, usually while hunting on the wing at a height of at least 200 m. In Norway, plunge-diving is considered rare. At times they will also fish by wading into shallows, often from shores or gravel islands. The species will at times variously follow fishing boats, readily exploits commercial fisheries, stocked lakes, carp ponds and the like, and scavenges dead fish or fish-offal in a wide range of situations. When it comes to non-fish prey, it has been said that white-tailed eagles often hunt by flying low over sea coast or lakeshore and attempt to surprise victims. However, the hunting success rates on healthy birds can be low as revealed in studying wintering eagles in Sweden attempting to hunt mallards (Anas platyrhynchos). White-tailed eagles also regularly pirate food from otters and other birds including cormorants, gulls, ospreys, corvids and various other raptors. Carrion is often the primary food source during lean winter months, with fish and ungulates preferred but everything from cetaceans to livestock to even humans being eaten after death. From studies of captive white-tailed eagles, daily food requirements were estimated at 500 to 600 g, which is equivalent to about 10% of the birds' body weight, with crop contents commonly of 190 - 560 g. Some semi-captive juveniles on the isle of Rùm, Scotland could eat up to 1.4 kg in one sitting. However, in Norway, it was estimated that a family of wild white-tailed eagles including each adult and 3 fledglings were consuming on average up to 625 g per bird each day. Furthermore, one male consumed an estimated 2 kg in a single meal upon capturing a large fish. The crop can bulge to the size of a small grapefruit after they've consumed a large meal.

Many studies have reflected that the primary foods of white-tailed eagles are fish and water birds. These are the primary food as well for other sea eagle species. However, unlike most Haliaeetus, including the bald eagle and Steller's sea eagle, the water birds tend to take the primary position in the diet. From 26 accumulated food studies for this species, prey remains and pellets show that about 48.5% of the diet is made up of birds, 39.95% by fish, 9.95% by mammals and 1.6% by other foods. In total, more than 300 prey species are known throughout the bird's range. However, based on studies of prey remains and pellets in laboratories from Greenland white-tailed eagles, birds were shown to be biased in both kinds of remains (pellets and prey remains) whereas in situ study and direct nest observation favor fish. Going on pellet/remains alone here in Greenland from 557 items in the 1979 study, 68% of the diet would’ve been represented by birds and only 20% by fish but comprehensive observation shifted it to show fish were the primary food at 58% and birds were secondary at 30%. This study claimed this is often because the bones of fish are dissolved by the large digestive tract of the eagles upon consumption and may thus leave almost nothing in remains and to some extent in pellets. Subsequent studies here showed a much stronger preference for fish in Greenland by 1983, as fish comprised an extreme 91.8% of 660 items. However, this kind of direct continuous observation of food deliveries to nests is not always possible. Furthermore, despite similar bias for prey that is large and leaves conspicuous remains (including any larger fish, bird or mammal), in the bald eagle it was found that fish were usually detectable and dominant in remains and pellets. Most modern biologists may need to leave some fish unidentified but will account for different methodologies of prey study to get the most complete picture attainable. During winter, mammal prey can become more important in foods locally, as indicated in Scotland and shown in Norway and eastern Germany. As much as 41% of the diet can be made up of mammals, as was the case on the Kola Peninsula. There is evidence of strong seasonal shifts in food habits in several parts of the range, usually the largest portions of fish are caught during warmer months while birds and mammals are more important in the colder months, especially in coastal areas such as Norway when preferred fish prey often move to deeper water during winter. Among both fish and bird prey, it is thought that a majority that are caught weigh between 0.5 and 3 kg. At times it has been said that “most” prey of white-tailed eagles will weigh only 0.5 to 1 kg. However, the mean prey sizes caught can show greater variability. Three studies showed that mean prey size varied from 578 g in the Wigry National Park, Poland, 1062.1 g in the Rybinsk Reservoir, Russia and 1.72 kg in the Volga-Kama Nature Reserve, Russia. Thus, the mean prey size falls just slightly short of the mean prey mass of the golden eagle, which globally averages about 1.35 to 1.63 kg.

Fish

Overall, nearly 70 species of fish are known to be taken from throughout the white-tailed eagle's range. White-tailed eagles can hunt fish in fresh or saltwater as well as those that prefer brackish water areas. However, they are basically restricted to taking fish in extremely shallow water, often by preference in water less than 1 m deep. Ideal fishing areas can be found in areas such as the Baltic sea, where low coasts and archipelagos often have relatively shallow water. While healthy, large fish are often taken as well, white-tailed eagles often take out sickly, injured or already dead fish. In some cases, the fish prey will float to the surface when infected by fish tapeworm, as is often the case with some fish families such as carp. Fish are also caught after being battered, injured and killed at power plants, from large-scale fishing nets or are taken directly from human fishermen. Benthic fish tend to cling to rocks or sandy soil in shallows may be more vulnerable since they tend to look downward rather upward and are less competent at escaping predators coming from above the water's surface. Therefore, lurking benthic fish such as lumpsuckers are more vulnerable than many. Besides vulnerability, habitat and prey behaviour, fish body size may be a driver in the piscivorian dietary preferences. Studies have indicated that fish less than 20 cm are taken infrequently, since they have a lower yield, fish of up to 30 cm are taken secondarily and fish between 30 and 60 cm are preferred since they have the highest nutritional benefit. Fish taken can exceed 0.9 to 1 m but since they can start to considerably exceed the weight of the eagle itself, they may be prove too difficult to overpower. One large Atlantic halibut (Hippoglossus hippoglossus) was found with the disembodied feet of a white-tailed eagle still imbedded in its back, presumed the eagle drowned after being overpowered and drug under only to rot off, leaving only feet. Since they do not have the waterproofing oils on the plumage of the more accomplished raptorial diver, the osprey (Pandion haliaetus), white-tailed eagles prefer not to get their feathers wet as it can take a long time for them to dry. This may also make them vulnerable to losing their catch to other white-tailed eagles since their flight may be impaired until the wings are dried. Therefore, when hunting fish, they will almost always take flight as soon as possible to a feeding perch or nest. The largest fish lifted in flight and flown off with have been claimed anecdotely to reach weights of as much as 15 kg in the case of an Atlantic halibut in Norway. However, this is likely reported in error as no living eagle would likely be able to take flight with this heavy a load as they are more or less constrained to carrying in flight a load more or less equal to their own body weight, and even then only laboriously and in favorable wind conditions. The same Norwegian study coincided that another eagle when trying to fly with an Atlantic cod (Gadus morhua) weighing about 8 kg, the fish was quickly dropped as it was apparently deemed too heavy. The widely reported case of a white-tailed eagle carrying off a 3.5-year-old girl in Norway flight by the back of her dress only to drop her mostly unharmed below the eagle's eyrie, which was included in the Guinness Book of World Records, is considered most likely to be apocryphal since she weighed approximately 18 kg, far too heavy for any living eagle to lift in flight. Another option when taking particularly large fish is for the eagle to stay in water and row, swimming using their wings, across the water to the nearest bank or shore. While this would leave them waterlogged, of course, the food yield from such a catch is obviously attractive. White-tailed eagles have been photographed doing this with a large fish successfully in Greenland and 35 such cases were reported in Norway alone.

The most frequently recorded prey species in 18 food studies from across the range is the northern pike (Esox lucius), present in at least 16 of those studies. Pike were found to be the main prey species in both the Baltic Sea and Lapland in Sweden, at three breeding locations in Finland, in two studies from Germany and in Belarus. The maximum representation of pike known was in Lapland, Sweden where they comprised 38.2% of 809 food items. Considered a top predator in many freshwater ecosystems (and thus with less significant anti-predator camouflage), the pike may be more conspicuous than many fish to hunting eagles due to the fish's boldly speckled flanks. While an average mature weight for a pike is around 1.4 kg, white-tailed eagles often attack larger sized pike, with an estimated average weight range of 2 to 5 kg. Some pike taken by white-tailed eagles were even estimated to weigh around 12 kg, however the eagle would be unable to fly with such a large catch and would need to row it to the nearest shore. The next most widely reported fish prey species is the common bream (Abramis brama). This bream was reported in 10 of 18 dietary studies and was the main prey in the Polesie State Radioecological Reserve, Belarus, in the Ural mountains region of Russia, and in the Kostomuksha Nature Reserve, Russia. Like the pike, the relatively large size of common bream, which weigh about 1.09 kg on average, can prove attractive to hunting eagles. They are also vulnerable to tapeworms so can be easily taken while floating close the water's surface in ill condition.

Many varieties of fish are taken opportunistically and randomly, as opposed to pike and bream, which can locally appear to be selected out of proportion to their regional population. Particularly diverse in the white-tailed eagle's prey spectrum are the family Cyprinidae, of which more than 20 species are known to be predated including the common bream. Others taken with some preference may include salmonids and cod and their allies, both families known to obtain relatively large body sizes and occasional habituate shallow water, as well as lumpsuckers, because they are benthic. In Greenland, the leading prey species is the salmonid, the Arctic char (Salvelinus alpinus), which comprised 27.2% of 660 prey items. The secondary prey in Greenland was recorded as two species of cod. While the Arctic char can average up to 2.53 kg and cod can sometimes grow considerably larger than that, the average weight of cod taken here was estimated at only 420 to 640 g and the average char at 660 to 740 g. In Norway, of 524 fish prey items, the common lumpsucker (Cyclopterus lumpus), which averages up to 1.43 kg but is usually smaller, made up 24% of fish taken and the 2.13 kg Atlantic wolffish (Anarhichas lupus) made up 17% of fish taken. However, fish were secondary to birds overall in Norway. Per two studies from Sweden, fish were usually the main food unlike in Norway and Finland and could comprise from 51-60% of the diet. Fish were also somewhat dominant in the foods from two studies in Belarus, making up 48.1-53.7% of the diet. Fish similarly were important to nesting eagles in Hokkaido, where 54% of 533 prey items were fish, led by the 800 g Alaska pollock (Gadus chalcogrammus) at 18.4%. In different studies of the Danube Delta of Romania, from 44.6% to 79% of the diet was comprised by fish, led by the common carp (Cyprinus carpio) and Prussian carp (Carassius gibelio). In the Kostomuksha Nature Reserve of Russia, fish were strongly dominant in food remains, making 80% of the known diet.

Birds

White-tailed eagles are known to prey on about 170 species of bird, the most diverse group in their prey spectrum. While hunting birds, this massive, relatively slow-flying eagle requires an element of surprise, with often a tactful use of cover or bright sunlight upon the approach from a nearby perch. For example, grey herons (Ardea cinerea) have been caught after an eagle used a low flight over turbulent water to ambush them. However, even with a stealthy attack, the waterfowl favored in the avian diet tend to be highly wary and will more often than not escape. The white-tailed eagles must then attack birds at times of vulnerability or injury, or will often utilize the prey's escape tactics against them. Diving ducks and other diving water birds will be taken preferentially where they are available. In hunting diving birds, they utilize a technique of forcing the birds to dive repeatedly to avoid attacks, until the victim is exhausted from the efforts and can then be caught. Usually while hunting like this, the white-tailed eagle tends to circle low to stay close to the intended victim, with birds diving in shallower water being preferred. Ducks with conspicuous plumage, such as male common eiders (Somateria mollissima), with their pale plumage, may be easier to see under water and so may be taken somewhat more via this hunting method. Beyond waterfowl, both loons and grebes have been seen to be successfully hunted in this way. Eagles were recorded doing between 7 and 12 attacks on eiders in Russia and were usually successful in procuring prey. Even as many as 65 passes have recorded in less than 45 minutes but more than a few attacks also start to exhaust the eagle, as one immature gave up after 15-28 attempts at a little grebe (Tachybaptus ruficollis). While bald eagles may attack diving ducks in the same way, they appear to do so somewhat less regularly and successfully. White-tailed eagles usually have less success hunting dabbling ducks because their normal predator response behavior is to take flight. In one instance, a mallard was caught while flying in mid-air, but usually the much larger eagle is unable to capture ducks in flight. While somewhat less swift in flight, healthy geese can usually outpace a heavier eagle as well and one bean goose (Anser fabalis) was even recorded to have defended itself successfully against an eagle's attack even though this goose was injured. White-tailed eagles often hunt dabbling ducks and geese most successfully when they are molted into their eclipse plumage which renders them temporarily flightless. Swans during winter may find themselves forced to land due to their bulk on a sheet of ice over water if they can find no open water, which can make their feet stuck to the ice. White-tailed eagles have been recorded utilizing this disability to attack and kill swans. They've also been seen to attack numerous waterfowl when the birds are injured by buckshot from duck hunters. Due to their status as enemy of other large birds, they are frequently mobbed by them and white-tailed eagles have been recorded utilizing violent mobbings to suddenly turn over in flight and predaceously grab one of the birds mobbing them, including large gulls and even a northern goshawk (Accipiter gentilis). As an opportunistic predator, it often takes young birds freely as well as adult and fledged juvenile birds. In general, due to different nesting situations, white-tailed eagles instead of dabbling or diving water birds usually attack the more conspicuous or open nests of gulls, those of several other types of seabird, large corvids or other accipitrids. In Germany and Scotland, up to 86% of gulls taken were nestlings and juveniles. Cases of white-tailed eagles eating eggs, instead of nestlings or older birds, is considered rare. Nonetheless, they have been recorded eating a few eggs, which they may carry in their beaks rather in their feet, of some seabirds such as kittiwakes, eiders, cormorants and gulls.

The most widely recorded avian prey species and, second most widely recorded prey species behind the pike, is the 1.14 kg mallard, due to its circumpolar range and commonality in many wetlands areas. However, as aforementioned, healthy mallards are difficult for white-tailed eagles due to their tendency to fly at first sign of danger. However, exploiting the mallard's flightlessness during eclipse plumage may result in eagles hunting them intensely only in late summer. Due to this mallards are usually a secondary prey species year around. The largest known representation of mallards in the diet were from Müritz National Park, Germany, where mallards were the 3rd best represented prey species at 10.1% of 247 items and from Augustów Primeval Forest, Poland, where mallards were the 2nd most numerous prey and made up 9.84% of 803 items. Taken more preferentially where they occur are common eiders. When hunting eiders, perhaps the largest of diving ducks at a mean weight of 2.06 kg, white-tailed eagles frequently force the eider to dive repeatedly until it is exhausted and can be captured. When sitting on the nest, the female common eider will try to escape in flight but is a relatively weak and ponderous flier and so too may be often victimized by the eagles. Otherwise the pale plumage of adult male common eiders while they're diving is reported to make them more vulnerable to eagle attacks. Eiders were the leading prey species in Norway making 18.8% of 1612 prey items, as well as in the Åland Islands, Finland where the eider comprised 18.63% of 5161 prey items (thus nearly a thousand eiders were taken here). Eiders also appeared to be the main prey species in Iceland. There is evidence that a growing white-tailed eagle population is having a net negative effect on eider numbers in some areas, and locally eiders have altered to partial nocturnal foraging apparently to avoid hunting eagles. In inland regions, an avian prey species preferred by white-tailed eagles is the 836 g Eurasian coot (Fulica atra). The coot is the second most widely represented bird prey species (and fourth species of any class known overall) in 18 dietary studies. Coots bunch together in marshy spots when approached by a flying eagle and as many as 5 eagles at once have been recorded attacking large flocks on the water. Coots behaviour often endangers them to large raptors: they seldom dive, are weaker and slower fliers than most water birds and are collectively often less wary and more approachable than most waterfowl are. Coot were strongly the dominant food in Wigry National Park, Poland where they made up 44.1% of 299 items, and were also the leading prey in Augustów Primeval Forest, Poland where they made up 11.59% of the foods. Overall at Wigry and Augustów, birds altogether made up 66.2% and 47.83% of the diets, respectively. In the Danube Delta, Romania, birds climbed in importance of the diet from 21% in 1970 to 50% by 2015, thanks largely to increased numbers of coots.

In total, about 38 species of waterfowl are known to be hunted, as well as all available species of loons and grebes, several types of rails, tubenoses as well as herons, storks and other assorted large waders. White-tailed eagles also are known to hunt some 42 species of shorebird, most significantly gulls and alcids. Even shorebirds as small as 21.1 g little stint (Calidris minuta), 62.6 g wood sandpiper (Tringa glareola) and 64 g common ringed plover (Charadrius hiaticula) are known to be preyed upon, albeit quite rarely. More than a dozen gulls are known in the prey spectrum from the smallest to all four largest extant species. In the United Kingdom, northern fulmar (Fulmarus glacialis) are noted as a common prey species and as such may contribute to locally high levels of DDT and PCB chemicals in nesting eagles. However, fulmars defend themselves by regurgitating a smelly, tar-like oily substance that can impair the flight of predators and may even kill some intended predators when it is in large quantity, and young juvenile eagles, being less cautious and experienced, are most prone to being severely “oiled”. Alcids such as murres tend to become especially important in the diet of eagles in coastal Norway during winter, especially near offshore islands, when coastal fish tend to move to deeper waters. At least 8 species of dabbling duck are known in the prey spectrum. Due to the social inclination of dabbling ducks, they perhaps have the most success hunting isolated birds but they've also been taken from panic-stricken flocks as well. Despite the difficulty of taking them, dabbling ducks of unidentified species were found to be the main food of white-tailed eagles in Lake Baikal, where they comprised 51.8% of 199 prey items. In Fennoscandia, they are attracted to coastal waters during winter to attack large numbers of diving ducks including eiders, common goldeneye (Bucephala clangula), common (Mergus merganser) and red-breasted mergansers (Mergus serrator), tufted ducks (Aythya fuligula) and scoters. Year around in the Åland Islands, 66.2% of 5161 food items were birds, while in the 3 sites in different parts of Finland birds made up 51.1% of 3152 food items. In Germany, 52.4% of 1637 prey items were birds, mostly coots and unidentified waterfowl. More locally in Germany, in Müritz National Park the percentage of birds in the diet climbs to 65.73% Birds were strongly dominant in food records from Scotland, making up 73.53% of 1930 prey items, and in Kandalaksha Nature Reserve, where they comprised 75% of 523 prey items.

While most of the aforementioned water birds are modest of size and taken largely due to ease (diving water birds, whether healthy or infirm, and usually infirm or molting dabbling water birds), white-tailed eagles routinely attack larger water birds as well. In many areas, large numbers of 3.31 kg graylag geese (Anser anser), Europe's largest native wild goose, are taken. For example, they were the main prey, making up 28.2% of 192 prey items, for wintering eagles in Oostvaardersplassen, Netherlands, and the 2nd most often recorded prey species in both Müritz National Park, Germany, where they made up 16.42% of 247 prey items, and in Austria, where they made up 9.5% of 349 items. White-tailed eagles are known to prey on at least 10 species of geese, ranging in size from the 1.23 kg red-breasted goose (Branta ruficollis) to the non-native 3.69 kg Canada goose (Branta canadensis). They will take many goslings during summer, as greylag goslings alone can comprise up 23% of the seasonal bird prey, and fully-grown geese in other seasons. Large waders are taken when possible, including a half dozen heron species, and, larger still, both the young and adults of 5.5 kg common cranes (Grus grus) and both the 2.93 kg black and the 3.44 kg white stork (Ciconia ciconia). Black and white storks are primary prey species in the Polesie State Radioecological Reserve, Belarus where they comprised 12.6% (2nd most regular prey species) and 6.3% (4th most regular) of the diet, respectively. Large numbers of black stork were also taken in Augustów Primeval Forest where nearly 50 were found around eagle nests. They are reported to have attacked and eaten the largest seabirds they encounter, such as great cormorants (Phalacrocorax carbo) and in some cases, such as in the Baltic sea, have nearly destroyed whole colonies, from the eggs to the adults which average about 2.57 kg. In the Estonian island of Hiiumaa, home to at least 25 pairs of sea eagles, as many as 26 individuals have been observed simultaneously culling a single cormorant colony. Similarly large numbers were taken of the 2.82 kg Japanese cormorant (Phalacrocorax capillatus), which was the second most numerous prey species, making up 11.63% of 533 prey items in Hokkaido, and opportunistically, when their north Atlantic colonies are accessed, great numbers of 3 kg northern gannets (Morus bassanus). Vagrant white-tailed eagles in Hawaii were recorded to prey on several Laysan albatross (Phoebastria immutabilis) and were suspected to prey on black-footed albatross (Phoebastria nigripes), both weighing about 3.17 kg. Another large water bird taken as adults are 4.98 kg common loons (Gavia immer). However, the largest water birds they are known to kill are adult swans, including mute (Cygnus olor), whooper (Cygnus cygnus) and Bewick's swans (Cygnus columbianus bewickii). While cygnets and disabled birds (either by natural conditions such as ice or by human hunters) are at the greatest risk

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Scientific classification

Kingdom
Animalia
Phylum
Chordata
Class
Aves
Order
Accipitriformes
Family
Accipitridae
Genus
Haliaeetus
Species
Haliaeetus albicilla

Common names

  • Thai: นกอินทรีหางขาว, nok in-sree hang khao

Conservation status

Least Concern (IUCN3.1)

Least Concern (IUCN3.1)

Range Map