White-tailed Eagle
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| Haliaeetus albicilla (Linnaeus, 1758) |
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Falco albicilla Linnaeus, 1758 |
The White-tailed Eagle (Haliaeetus albicilla[1]), also known as the Sea Eagle, Erne or White-tailed Sea-eagle is a very large bird of prey in the family Accipitridae which includes other raptors such as hawks, kites and harriers.
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[edit] Description
The White-tailed Eagle is a huge bird, 76-92 cm long with a 200-250 cm wingspan. Females are significantly larger than the males. The White-tailed Eagle has broad "barn door" wings, a large head and thick "meat-cleaver" beak. The adult is mainly brown except for the paler head and neck, 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.
[edit] Distribution and systematics
This is a very large eagle which breeds in northern Eurasia. It was successfully re-introduced to the Isle of Rum, in the Small Isles archipelago in Scotland, in 1975 and now breeds throughout the Western Isles and Small Isles as well as the islands of Mull, Skye, Lewis, Canna and the mainland coast of Wester Ross. The White-tailed Eagle is still a rare breeder in Britain following its extinction and reintroduction. The largest population in Europe is found along the coast of Norway.
On May 22, 2006 it was announced that pair of White-tailed Eagles was breeding in a nature reserve Oostvaardersplassen in the Netherlands. This is the first time the bird has bred in the Netherlands in modern times.
White-tailed Eagles are mostly resident, only the northernmost birds such as the Siberian population migrating south in winter.
A small resident population exists in southwesternmost Greenland and western Iceland. The former have been proposed as a distinct subspecies groenlandicus based on their very large size, but altogether this species is considered monotypic and the size variation is clinal according to Bergmann's Rule.
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 latest, possibly - if the most ancient fossil record is correctly assigned to this genus - as early as the Early/Middle Oligocene, some 28 mya (Wink et al. 1996[2]). 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.
[edit] Diet
The Eagle's diet is varied, including fish, birds, carrion and sometimes rodents. They regularly pirate food from otters and other birds. During the breeding season they require 500-600g of food per day when actively rearing young. During the winter months they tend to be inactive most of the day and their intake falls to 200-300g per day.
[edit] Breeding
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 claws 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 of the White-tailed Eagle 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. 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 30-70 km², normally in sheltered coastal locations. Sometimes they are found in-land by lakes and along river systems. The territory of the White-tailed Eagles can overlap with the territory of the golden eagle, though competition between the two species is limited. Golden eagles prefer mountains and moorland, while the White-tailed Eagle prefers the coast and the sea.
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-six weeks and they fledge at eleven-twelve weeks, remaining in the vicinity of the nest, dependent on their parents for a further six-ten weeks.
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 usually killed by the first-hatched sooner or later, as in most birds of prey.
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.
[edit] Near-extinction in Europe, and subsequent recovery
White-tailed eagles are alpha predators. Therefore, they tend to bioaccumulate environmental pollutants that are present in their prey. During the 1950-60s, white-tailed eagles in many regions in Europe underwent dramatic declines, and even went locally extinct. Intense conservation actions (legal protection to decrease hunting, protection of breeding sites and winter feeding) led to a recovery of white-tailed eagle populations in Europe. Thus, the eagle has today re-colonized many traditional breeding areas in Europe, although the recovery is still on-going.
Recent microsatellite and mitochondrial DNA studies of white-tailed eagles in North-central Europe (Hailer et al. 2005, 2006) showed that the recovering population has retained appreciable amounts of genetic diversity, implying low risk of inbreeding depression (a serious concern in wide-ranging, long-lived species with low population density), making the recovery of this species a true success story for nature conservation.
[edit] Heraldry
The White-tailed Eagle is believed to be the one shown in the Polish Coat of Arms.
[edit] References
- BirdLife International (2005). Haliaeetus albicilla. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 24 August 2006. Database entry restates that the White-tailed Eagle has been downlisted to Least Concern in 2006.
- Hailer, Frank; Helander, Björn; Folkestad, Alv O.; Ganusevich, Sergei A.; Garstad, Steinar; Hauff, Peter; Koren, Christian; Nygård, Torgeir; Volke, Veljo; Vilà, Carles & Ellegren, Hans (2006): Bottlenecked but long-lived: high genetic diversity retained in white-tailed eagles upon recovery from population decline. Biology Letters 2(2): 316-319. DOI:10.1098/rsbl.2006.0453 PDF fulltext Electronic appendix
- Hailer, Frank; Gautschi, Barbara & Helander, Björn (2005): Development and multiplex PCR amplification of novel microsatellite markers in the White-tailed Sea Eagle, Haliaeetus albicilla (Aves: Falconiformes, Accipitridae). Molecular Ecology Notes 5(4): 938-940. DOI:10.1111/j.1471-8286.2005.01122.x (HTML abstract)
- Wink, M.; Heidrich, P. & Fentzloff, C. (1996): A mtDNA phylogeny of sea eagles (genus Haliaeetus) based on nucleotide sequences of the cytochrome b gene. Biochemical Systematics and Ecology 24: 783-791. DOI:10.1016/S0305-1978(96)00049-X PDF fulltext
[edit] Footnotes
- ^ Etymology: Haliaeetus, New Latin for "sea-eagle". albicilla, "white-tailed", from Latin albi- "white" + cilla, "tail".
- ^ The authors' reservations about using the generalized "2%" rate of molecular evolution have since proven to be well-founded.
[edit] External links
- NaturePhoto-CZ: White-tailed Eagle photos. Retrieved 2006-NOV-30.
- RSPB: White-tailed Eagle. Retrieved 2006-NOV-30.
