White-tailed eagle
| White-tailed Eagle | |
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| Adult in flight | |
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| Species: | H. albicilla
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| Binomial name | |
| Haliaeetus albicilla (Linnaeus, 1758)
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| Light Green: nesting area Blue: wintering area Dark Green: all-year | |
| Synonyms | |
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Falco albicilla Linnaeus, 1758 | |
The White-tailed Eagle (Haliaeetus albicilla[1]), also known as the Sea Eagle, Erne (sometimes Ern), 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. It is considered a very close cousin of the American Bald Eagle and occupies the same ecological niche in Eurasia.
Description
The White-tailed Eagle is a large bird, 70-90 cm long with a 200-240 cm wingspan. Females, weighing 4–6.9 kg, are significantly larger than the males, which weigh 3–5.4 kg. It 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, 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.[2]
Distribution and systematics
This large eagle breeds in northern Europe and northern Asia. The largest population in Europe is found along the coast of Norway. They are mostly resident, only the northernmost birds such as the eastern Scandinavian and Siberian population migrating south in winter.
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, but the species is now considered monotypic and the size variation is clinal according to Bergmann's Rule.[3]
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/middle Oligocene, about 28 mya ago.[4]
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
The Eagle's diet is varied, including fish, birds, carrion and, occasionally, small mammals. Many birds live almost wholly as scavengers, regularly pirating food from otters and other birds, but 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.[5] Although a less active hunter than the Golden Eagle, and usually losing out to them in direct competition for a single food item, they can exist at higher population densities and out-compete Golden Eagles because of their longer gut and more efficient digestive system, being able to live better with less food.[6]
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 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.[2] 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 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.
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 Eagles are alpha 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[6]) 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 throughout western, central and southern Europe except for Norway and western Iceland. Intense conservation actions (legal protection to decrease hunting, protection of breeding sites and winter feeding) led to a recovery of populations in eastern Europe, and a steady spread back westward, particularly in the southern Baltic Sea area from Poland west to Germany and Denmark. It has today re-colonised some traditional breeding areas in Europe and the recovery is still on-going, assisted in Great Britain and Ireland by re-introduction schemes.[5][2]
Some threats still remain, notably illegal persecution by gamebird shooting interests and egg thieves in Scotland,[7] 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.[8][9]
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 the mainland coast of Wester Ross. The White-tailed Eagle is still a rare breeder in Britain following its extinction and reintroduction, with 36 pairs in 2006.[2][7]
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. Early in 2007 the eagles returned to their nest.[10].
The White-tailed Eagle is being re-introduced to the Republic of Ireland, starting in the summer of 2007. Fifteen young eagles from Norway will be released in Killarney National Park in County Kerry 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 after persecution from landowners. Fifteen chicks will then be brought in annually for the next five years.[11]
Recent microsatellite and mitochondrial DNA studies of White-tailed Eagles in North-central Europe 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.[12][13]
Heraldry
The White-tailed Eagle is believed to be the one shown in the Polish Coat of Arms.
References
- ^ Etymology: Haliaeetus, New Latin for "sea-eagle". albicilla, "white-tailed", from Latin albi- "white" + cilla, "tail".
- ^ a b c d Snow, D. W. & Perrins, C. M. (1998). The Birds of the Western Palearctic Concise Edition. OUP ISBN 0-19-854099-X.
- ^ del Hoyo, J., Elliott, A., & Sargatal, J., eds. (1994). Handbook of the Birds of the World Vol. 2. Lynx Edicions, Barcelona ISBN 84-87334-15-6.
- ^ 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. The authors' reservations about using the generalised "2%" rate of molecular evolution have since proven to be well-founded.
- ^ a b Cramp, S., ed. (1980). The Birds of the Western Palearctic Vol. 2. Oxford ISBN 0-19-857505-X.
- ^ a b Halley, D. J. (1998). Golden and White-tailed Eagles in Scotland and Norway. Coexistence, competition and environmental degradation. British Birds 91 (5): 171-179.
- ^ a b RSPB: Birds of prey: Which birds are threatened?
- ^ BirdLife International: Wind farm causes eagle deaths
- ^ Birding News: Arrivals & Alarms
- ^ The Dutch national forestry, who owns the reserve, has put up a webcam trained on the nesting eagles [1]
- ^ RTÉ: Rare eagle reintroduced to Ireland
- ^ Hailer, F., Helander, B., Folkestad, A. O., Ganusevich, S. A., Garstad, S., Hauff, P., Koren, C., Nygård, T., Volke, V., Vilà, C., & Ellegren, H. (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, F., Gautschi, B., & Helander, B. (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 (Abstract)
- Template:IUCN2006 Database entry restates that the White-tailed Eagle has been downlisted to Least Concern in 2006.
External links
- NaturePhoto-CZ: White-tailed Eagle photos. Retrieved 2006-NOV-30.
- RSPB: White-tailed Eagle. Retrieved 2006-NOV-30.