The white-tailed eagle (Haliaeetus albicilla) also called the sea eagle and 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.
The white-tailed eagle is a very large bird. It measures 66–94 cm (26–37 in) in length with a 1.78–2.45 m (5.8–8.0 ft) wingspan. The wingspan, with a midpoint of 2.18 m (7.2 ft), is on average the largest of any eagle.] The Steller's sea eagle, larger in both weight and total length, is the closest rival for median wingspan amongst living eagles. The bald eagle is roughly the same size as the white-tailed eagle, although has a shorter average wingspan and usually longer total length, due to a longer tail. 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).
The record weight for the species 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. ] Among standard measurements, the wing chord is 55.2–71.7 cm (21.7–28.2 in), the tail is 25–33 cm (9.8–13.0 in), the tarsus is 9.2–10.1 cm (3.6–4.0 in) and the exposed culmen is 6–6.5 cm (2.4–2.6 in). The measurements of eagles from Greenland are in general larger than in other populations of the species. 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.
This species has broad "barn door" wings, a large head and a large thick beak. The adult is mainly grayish-brown except for the slightly paler head and neck, blackish flight feathers, and distinctive white tail. All bare parts are yellow in color, including both the bill and the legs. In juvenile birds, the tail and bill are darker, with the tail becoming white with a dark terminal band in sub-adults. The combination of mousy-brown coloration, broad, evenly held wings, white tail, strong yellow bill and overall large size render the white-tailed eagle essentially unmistakable in its native range. Some individuals have been found to live over 25 years, 21 years being the average.
The white-tailed eagle's diet is varied, opportunistic and seasonal. Prey specimens can often include fish, birds and mammals. Many birds live largely as scavengers, regularly pirating food from otters and birds including cormorants, gulls, ospreys and various other raptors. Carrion is often the primary food source during lean winter months, with fish and ungulates being preferred but everything from cetaceans to livestock to even humans being eaten after death. They are often dominant among the scavengers in their range, over all but perhaps the largest carnivorous mammals i.e. gray wolves,
However, this eagle can be a powerful hunter as well. In Scotland the diet of this species differs significantly from that of sympatric golden eagles, as is also the case in Norway. The daily food requirement for a white-tailed eagle is in range of 500–600 g (1.1–1.3 lb). Although generally 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.
Virtually any fish found near the surface is potential prey for the white-tailed eagle. Commercial fisheries and carp ponds are readily exploited by the eagles when available Although they occasionally kill and harass some land birds, given the opportunity, white-tailed eagles usually target water-based birds as prey.In the Baltic the diet of this species 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 and in some cases destroyed whole colonies. 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. 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 eagles. Additionally, loons, grebes, ducks, coots, auks, gulls, geese and even swans have been preyed upon. Adults, nestlings and eggs of other birds are all regularly consumed. When targeting non-nesting birds, they often fly towards a waterbird repeatedly, forcing it to dive again and again, until the bird is exhausted and more easily caught.
When very large prey is killed, such as swans, the prey may be dragged along the surface of the water to the shore to be consumed. Live mammals consumed have ranged in size from voles to lambs and deer calves, the latter likely around the same size as the record-sized deer flown with by bald eagles in North America.
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. 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.
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.
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