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White-tailed eagle

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White-tailed Eagle
In captivity
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Aves
Order:
Falconiformes
(or Accipitriformes, q.v.)
Family:
Accipitridae
Genus:
Haliaeetus
Species:
H. albicilla
Binomial name
Haliaeetus albicilla
(Linnaeus, 1758)
Light Green: nesting area
Blue: wintering area
Dark Green: all-year
Synonyms

Falco albicilla Linnaeus, 1758
Haliaeetus albicilla albicilla
Haliaeetus albicilla groenlandicus

The White-tailed Eagle (Haliaeetus albicilla[2]), also known as the Sea Eagle, Erne (sometimes Ern), or White-tailed Sea-eagle, is a large bird of prey in the family Accipitridae which includes other raptors such as hawks, kites, and harriers. It is considered a close cousin of the Bald Eagle and occupies the same ecological niche, but in Eurasia.

Description

The White-tailed Eagle is a very large bird. It measures 78–102 cm (31–40 in) in length with a 2.00–2.50 m (6.56–8.20 ft) wingspan. Females, typically weighing 4–6.9 kg (8.8–15.2 lb), are slightly larger than males, which weigh 3.1–5.4 kg (6.8–11.9 lb). 

 ′′ <refForestry Commissionary of Britain> ′′ . The record weight was 7.5 kg (17 lb) for a specimen from Scotland, while a more recent huge female from Greenland reportedly spanned 2.53 m (8.3 ft) across the wings.[3][4] The White-tailed Eagle is on average the largest european eagle and the fourth largest eagle in the world.[5] It has broad "barn door" wings, a large head and a thick "meat-cleaver" beak. The adult is mainly brown except for the paler head and neck, blackish flight feathers, distinctive white tail, and yellow bill and legs. In juvenile birds the tail and bill are darker, with the tail becoming white with a dark terminal band in sub-adults..[6][page needed]

Some individuals have been found to live over 25 years,[7] 21 years on average.[5]

Distribution and systematics

An adult eagle at Littleisland lighthouse warning its young to hide (which it did).
A young eagle above its nest at Littleisland lighthouse
Adult in flight in Isle of Skye, Scotland

This large eagle breeds in northern Europe and northern Asia. The largest population in Europe is found along the coast of Norway. The World population in 2008 stands at only 9,000 - 11,000 pairs.[5] They are mostly resident, only the northernmost birds such as the eastern Scandinavian and Siberian population migrating south in winter.


Greenland eagle

Small disjunct resident populations occur in southwesternmost Greenland and western Iceland. The former has been proposed as a distinct subspecies groenlandicus based on their very large size and body proportions. However, the species is now considered monotypic and the size variation is clinal according to Bergmann's Rule.[8][page needed] A recent genetic study of mitochondrial DNA[9] is consistent with this idea. Greenlandic white-tailed eagles are, on evolutionary time scales, a relatively recently founded population that has not yet accumulated a lot of unique genetic characteristics. However, the population appears to be demographically isolated and deserves special protection.

The White-tailed Eagle 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 ago.[10]

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 northern species, Steller's Sea Eagle, they have yellow talons, beaks, and eyes in adults.

Diet

Diving for fish near the Isle of Skye

The Eagle's diet is varied, including fish, birds, carrion, and, occasionally, mammals. Many birds live largely as scavengers, regularly pirating food from otters and other birds, and carrion is often the primary food source during lean winter months.[11] However, this eagle can be a powerful hunter as well. Locally, this species may compete fiercely with Golden Eagles over the rabbits and hares either eagle may catch. The daily food requirement is in the region of 500-600 g.[12][page needed] Although a less active hunter than the Golden Eagle, competition over food can go either way depending on the individual eagle. They can exist at higher population densities and typically outnumber Golden Eagles because of their longer gut and more efficient digestive system, being able to live better with less food.[13]

In the Baltic, the diet of the sea eagle consists mainly of sea birds (from the Little Tern to the Great Skua) and pike. Recently they are reported to have attacked and eaten great cormorants.[14] The cormorant is an invading species in the Baltic, and the sea eagle may prove a valuable culler of the cormorant population.[citation needed] In the UK, fulmar are noted as a common prey species and may contribute to locally high levels of DDT and PCB chemicals in nesting birds.[11]

Breeding

A juvenile (right) being mobbed by a pair of buzzards over the Isle of Canna

White-tailed Eagles are sexually mature at four or five years of age. They pair for life, though if one dies replacement can occur quickly. A bond is formed when a permanent home range is chosen. They have a characteristic aerial courtship display which culminates in the pair locking talons mid-air and whirling earthwards in series of spectacular cartwheels. White-tailed Eagles are much more vocal than Golden Eagles, particularly during the breeding season and especially the male when near the eyrie. Calls can sometimes take on the form of a duet between the pair.

The nest is a huge edifice of sticks in a tree or on a coastal cliff. Being faithful to their territories, once they breed, nests are often reused, sometimes for decades by successive generations of birds; one nest in Iceland has been in use for over 150 years.[6][page needed] In Scandinavia, trees have been known to collapse under the weight of enormous, long established nests.

The territory of the White-tailed Eagle ranges between 30 and 70 km², normally in sheltered coastal locations. Sometimes they are found inland by lakes and along rivers. The territory of the White-tailed Eagles can overlap with the territory of the Golden Eagle, and competition between the two species is limited. Golden Eagles prefer mountains and moorland, while the White-tailed Eagle prefers the coast and the sea. In adulthood, the White-tailed Eagle has no natural predators and is thus considered an apex predator.

Mated pairs produce one to three eggs per year. The eggs are laid two to five days apart in March or April and are incubated for 38 days by both parents. Once hatched, chicks are quite tolerant of one another, although the first hatched is often larger and dominant at feeding times. The female does most of the brooding and direct feeding, with the male taking over now and then. Young are able to feed themselves from five to six weeks and they fledge at eleven to twelve weeks, remaining in the vicinity of the nest, dependent on their parents for a further six to ten weeks. The sex of nestlings can be identified using field methods, or using DNA.[15]

Surplus chicks are sometimes removed from nests to use in reintroduction programs in areas where the species has died out. If left in the nest, they are often killed by the first-hatched sooner or later, as in most large eagles.

In such programs, the birds are raised in boxes on platforms in the tree canopy and fed in such a way that they cannot see the person supplying their food, until they are old enough to fly and thus find their own food.

Near-extinction and recovery in Europe

White-tailed eagle eyrie on the Shiant Islands in 1888.
A duel between white-tailed eagles close to their nest by Littleisland lighthouse, Lofoten, Norway.

White-tailed Eagles are apex predators. Therefore, they tend to experience bioaccumulation from environmental pollutants that are present in their prey, and also suffered intensive persecution by shepherds and gamekeepers who considered them (usually wrongly[13]) to be a threat to their livestock and gamebirds. During the period 1800-1970, White-tailed Eagles in most of Europe underwent dramatic declines, and became extinct in many regions of western, central, and southern Europe. While Norway, Germany, Poland, and Iceland harboured the largest surviving populations, pockets of reproducing pairs remained in several other countries.[16] Intense conservation actions throughout much of the remaining European distribution range (legal protection to decrease hunting, protection of breeding sites, and winter feeding) led to a recovery of many local populations. Since the 1980s, the European White-tailed Eagle population has recovered steadily, and is spreading back westward. It has today recolonised several traditional breeding areas in Europe and the recovery is still on-going, assisted in Ireland and the United Kingdom by reintroduction schemes.[6][page needed][12][page needed]

Some threats still remain, notably illegal persecution by gamebird shooting interests and egg thieves in Scotland,[11] and a new threat from wind turbines is emerging with significant mortality (considerably in excess of the area's population productivity) occurring at the Smøla Windfarm in Norway.[17][18]

It was successfully reintroduced to the Isle of Rum, in the Small Isles archipelago in Scotland, in 1975 and now breeds throughout the Western Isles and the mainland coast of Wester Ross. One of its Gaelic names is 'iolaire sùil na grèine' or 'eagle of the sunlit eye.'[5] In August 2008 fifteen chicks raised in Norway were released at a secret location in Fife, in expectation of reintroducing the species in the east coast of Scotland as well.[19] The White-tailed Eagle is still a rare breeder in Britain following its extinction and reintroduction, with 36 pairs in 2006 and 40 in 2008.[5][6][page needed][11]

On 22 May 2006 it was announced that a pair of White-tailed Eagles was breeding in the Oostvaardersplassen nature reserve in the Netherlands. They arrived on their own, not as a reintroduction. This is the first time the bird has bred in the Netherlands in modern times. In 2007, 2008 and 2009 the eagles returned to their nest.[20] In 2010, it turned out that the White-tailed eagle was also breeding in the Zwarte Meer nature district and in the Lauwersmeer area.[21]

The White-tailed Eagle is being reintroduced to Ireland. The program started in the summer of 2007. Fifteen to twenty young eagles from Norway are being released each spring into the Killarney National Park in the south-west of Ireland. This comprehensive project will last a number of years with many more eagles being released. The species has a rich history on the island but became extinct in Ireland in the 1800s due to persecution from landowners.[22]

In 2007, one hundred local sheep farmers gathered at Kerry airport to protest about the eagles arrival. Irish Farming Association Hill Committee chairman Mr O'Leary said he had no doubt the eagles would take lambs.[23]

Since their reintroduction seven eagles have been confirmed poisoned in County Kerry, two are suspected of having been poisoned and one was shot. A 13th eagle released in Kerry was shot in Northern Ireland.

Twenty more eagles are due for release in 2010. However, Dr Allan Mee, in charge of the sea eagle project, stated "the continuing loss of eagles to poisoning had cast a shadow over the future of the ambitious programme."[24]

Studies of microsatellite and mitochondrial DNA in White-tailed Eagles from North-central Europe have shown that the recovering European population has retained appreciable amounts of genetic diversity, implying low risk of inbreeding depression (a serious concern in species with low population density). Therefore, the recovery of this formerly endangered species is a true success story for nature conservation. The story also shows how local protection of a species can be successful, and important for preserving the species' evolutionary potential.[16][25][26]

Heraldry

The White-tailed Eagle is believed to be the White Eagle shown in the Polish Coat of Arms but also in the Serbian Coat of Arms.[27] The sea eagle is often blazoned holding a fish (usually a pike) on his talons, distinguishing him from an ordinary eagle.

Prehistory

On Orkney, sea eagle bones have been found in 6000 year old burial mounds, suggesting that the birds were revered by the prehistoric people there, a belief strengthened by the Pictish stone carvings of sea eagles from Orkney.[5]

Folklore

In the Shetland Isles fishermen believed that as soon as a sea eagle appeared fish would rise to the surface, belly up; this led to some fishermen using eagle fat, smeared on their bait, to increase their catch.[5]

Footnotes

  1. ^ IUCN redlist.
  2. ^ Etymology: Haliaeetus, New Latin for "sea-eagle". albicilla, "white-tailed", from Latin albi- "white" + cilla, "tail".
  3. ^ Wood, Gerald (1983). The Guinness Book of Animal Facts and Feats. ISBN 978-0-85112-235-9.
  4. ^ World's Largest White-tailed Eagle (2011).
  5. ^ a b c d e f g The Nature of Scotland, p. 49.
  6. ^ a b c d Snow & Perrins 1998.
  7. ^ "Merikotkien määrä lisääntyy". MTV3.fi. Retrieved 2011-05-30.
  8. ^ del Hoyo, Elliott & Sargatal 1994.
  9. ^ Hailer et al. 2007.
  10. ^ Wink, Heidrich & Fentzloff 1996.
  11. ^ a b c d [http://www.rspb.org.uk/wildlife/birdguide/name/enwiki/w/whitetailedeagle/feeding.aspx Cite error: The named reference "rspb" was defined multiple times with different content (see the help page).
  12. ^ a b Cramp 1980.
  13. ^ a b Halley 1998.
  14. ^ http://www.hs.fi/kotimaa/artikkeli/Turun+Sanomat+Merikotkat+oppineet+syömään+aikuisiakin+merimetsoja/1135256870866/?cmp=tm_etu_uusimmat_uutiset
  15. ^ Helander, Hailer & Vilà 2007.
  16. ^ a b Hailer et al. 2006.
  17. ^ BirdLife International: Wind farm causes eagle deaths
  18. ^ Birding News: Arrivals & Alarms
  19. ^ (BBC News) " Birds released in secret location" 13 August 2008. Accessed 13 August 2008.
  20. ^ The Dutch national forestry, which owns the reserve, has put up a webcam trained on the nesting eagles [1]
  21. ^ Van onze verslaggever Caspar Janssen. "Zeearend nestelt zich in Nederland - Binnenland - VK". Volkskrant.nl. Retrieved 2011-05-30.
  22. ^ RTÉ: Rare eagle reintroduced to Ireland
  23. ^ "Farmers protest at the arrival of the Eagles in 2007". DrimnaghBirdwatch.wordpress.com. Drimnagh Birdwatch. 2010-03-04. Retrieved 2011-05-30.
  24. ^ "Sea eagle death in Kerry park brings total to 13". The Irish Times. 2010-05-04. Retrieved 2011-05-30.
  25. ^ Hailer 2006.
  26. ^ Hailer, Gautschi & Helander 2005.
  27. ^ "Polish Birds Directory". birds.poland.pl. Retrieved 2011-05-30.
References
Cited works

Further reading

Identification
  • Grant, Peter J. (1988) The Co. Kerry Bald Eagle Twitching 1(12): 379-80 - describes plumage differences between Bald Eagle and White-tailed Eagle in juvenile plumage
Extinction in Scotland
  • Harvie-Brown, J. A. and Buckley, T. E. (1892). A Vertebrate Fauna of Argyll and the Inner Hebrides. Edinburgh : David Douglas. p. 104 - 107.
  • Harvie-Brown, J. A. and Buckley, T. E. (1888). A Vertebrate Fauna of the Outer Hebrides. Edinburgh : David Douglas. p. 84 - 87.
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