The White-tailed Eagle 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 in Eurasia.

The White-tailed Eagle is a large bird, 69–92 cm (27–36 in) long with a 182–244 cm (72–96 in) wingspan. Females, weighing 4–6.9 kg (8.8–15.2 lbs), are slightly larger than males, which weigh 3.1-5.4 kg (6.8–12 lbs). It is the fourth largest eagle in the World. 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.

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

This large eagle breeds in northern Europe and northern Asia.

The White-tailed Eagle forms a species pair with the Bald Eagle.

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. The daily food requirement is in the region of 500-600 g.

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.

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.

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.