The white-tailed eagle (Haliaeetus albicilla), sometimes known as the "sea eagle", is a large bird of prey, widely distributed across temperate Eurasia. Like other eagles, it is a member of the family Accipitridae (or accipitrids) which also 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.Helander, B., & Stjernberg, T. (2003). Action plan for the conservation of white-tailed sea eagle (Haliaeetus albicilla). In Convention on the Conservation of European Wildlife and Natural Habitats, Strasbourg, France. Sometimes, it is known as the ern or erne (depending on spelling by sources),Love, J. A. (1983). The return of the Sea Eagle. Cambridge University Press, . gray sea eagle and Eurasian sea eagle.Ridgway, R., & Friedmann, H. (1919). The birds of North and Middle America: a descriptive catalogue of the higher groups, genera, species, and subspecies of birds known to occur in North America, from the Arctic lands to the Isthmus of Panama, the West Indies and other islands of the Caribbean sea, and the Galapagos Archipelago (Vol. 50, No. 8). Govt. Print. Off.
While found across a wide range, breeding from as far west as Greenland and Iceland across to as far east as Hokkaido, Japan, they may be scarce and have thinly distributed nesting due to human activities, including habitat alteration and destruction of wetlands, about a century of systematic human persecution (from the early 1800s to around World War II) followed by inadvertent poisoning and epidemics of nesting failure due to chemical pesticides and organic compounds, which have threatened eagles since the 1950s and continue to be a concern. For these reasons, the white-tailed eagle was considered endangered or extinct in several countries.King, W. B., & Vincent, J. (1978). Endangered birds of the world, The ICBP Bird red data book (Vol. 2). Smithsonian Inst Press. Some populations have since recovered well, due to governmental protection, dedicated conservationists and naturalists protecting habitats and nesting sites, regulating poaching and pesticide usage, as well as careful reintroduction into their former range.Love, J. A. (1988). The reintroduction of the white-tailed sea eagle to Scotland: 1975–1987. Nature Conservancy Council.
White-tailed eagles live most of the year near large bodies of open water, including coastal saltwater areas and inland freshwater lakes, wetlands, bogs and rivers. It requires old-growth trees or ample sea cliffs for nesting, and an abundant food supply of fish and birds (largely water birds) over nearly any other prey. Both a powerful apex predator and an opportunistic scavenger, it forms a species pair with 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 Neo-Latin for "sea-eagle", from Ancient Greek hali-, "sea-" and aetos, "eagle". The specific albicilla, "white-tailed", is from Neo-Latin albi-, "white" and cilla, which is meant to mean "tail" but actually comes from a medieval misunderstanding of the Latin name motacilla for wagtails. The name originally meant "little mover", but certain writers thought it meant "wag-tail", giving rise to a new false Latin word cilla for "tail". The Anglo-Saxon name erne means "soarer", and it is cognate to Swedish örn and Finnish aarni. 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 monophyletic group comprising 11 living species, including the closely related Ichthyophaga fish eagles which may or may not be part of a separate genus. The latter group, comprising 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.Seibold, I., & Helbig, A. J. (1996). Phylogenetic relationships of the sea eagles (genus Haliaeetus): reconstructions based on morphology, allozymes and mitochondrial DNA sequences. Journal of Zoological Systematics and Evolutionary Research, 34(2), 103–112.Griffiths, C. S., Barrowclough, G. F., Groth, J. G., & Mertz, L. A. (2007). Phylogeny, diversity, and classification of the Accipitridae based on DNA sequences of the RAG‐1 exon. Journal of Avian Biology, 38(5), 587–602. 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.Olsen, J. (2016). Notes on Sanford's Sea-Eagle Haliaeetus sanfordi and Other Raptors in the Solomon Islands. Australian Field Ornithology, 17(2).
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.Seibold, I., & Helbig, A. J. (1995). Evolutionary history of New and Old World vultures inferred from nucleotide sequences of the mitochondrial cytochrome b gene. Phil. Trans. R. Soc. Lond. B, 350(1332), 163–178.Wink, M., & Sauer-Gürth, H. (2004). Phylogenetic relationships in diurnal raptors based on nucleotide sequences of mitochondrial and nuclear marker genes. Raptors worldwide, pp. 483–498. Other groups, beyond milvine kites and Old World vulture, of modern accipitrids that are seemingly in some way related, albeit 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 colouring and size (i.e. the eastern average slightly darker and smaller than more westerly ones).Oberholser, H.C. (1921). Journal of the Washington Academy of Sciences; Abstract: Ornithology. Washington Academy of Sciences. 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 (Haliaeetus leucoryphus), 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 occur in the Hawaiian Islands only 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 ~3,500-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.
Description
Size
The white-tailed eagle is one of the largest living birds of prey. It is the largest of the dozen species of eagle found in Europe and the largest eagle across its distribution, excluding the Russian Far East and (during the winter) Hokkaido, Japan, 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 the Steller's sea eagle (Haliaeetus pelagicus), the harpy eagle (Harpia harpyja) and the Philippine eagle (Pithecophaga jefferyi). The white-tailed eagle measures anywhere from in total length with a typical wingspan of . 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. The white-tailed eagle does appear to outsize the average wingspan of the wedge-tailed eagle (Aquila audax), which is sometimes also titled the largest winged extant eagle due to an exceptionally large individual shot in 1931, although the Steller's sea eagle may rival it in that respect.