White-tailed eagle

Name and taxonomy

Carl Linnaeus described the bird in 1758 as Falco albicilla. Marie Jules Cesar Savigny set up the genus Haliaeetus in 1809. He published it in the Description de l'Egypte. Haliaeetus is Neo-Latin for sea eagle, from the Greek words for sea and eagle. The second half of the name means white tail, and it rests on a medieval mistake. Scholars misread the Latin motacilla and invented a word cilla for a tail.

The old English name for the bird is erne, which means soarer. The Swedish orn and the Finnish aarni share that root. Gaelic has several names, among them one that calls the bird the eagle of the sun's eye. English also uses sea eagle, grey sea eagle and white-tailed sea eagle for the same species.

Evolution and relatives

The species belongs to the Accipitridae, the family of hawks, kites and harriers. Its genus holds up to eleven sea eagles worldwide. The white-tailed eagle and the bald eagle form a species pair. One holds the temperate north of Eurasia and the other the same ground in North America. The two look and behave so alike that a pale, worn adult can pass for a faded bald eagle.

The bill is heavy even for a sea eagle, at 45 to 65 millimetres of exposed ridge. The rear talon runs 37 to 46 mm and averages 40.9 mm. That claw is the largest a bird of this family carries. It is shorter than a golden eagle's and curves more sharply. The extra curve probably helps the bird hold a fish that is trying to slip free.

Appearance

The adult is a greyish mid-brown bird with little pattern. The head, neck and upper breast are paler, often a buff shade. A worn bird can bleach almost to cream. The short tail is white and shaped like a wedge, and it stands out against the brown. Bill, cere, feet and eyes are all yellow in an adult. The tail measures 25 to 33.1 centimetres in a grown bird.

A juvenile is much darker and far more blotchy, with pale feather edges below. Its head is blackish, its tail dirty grey-cream, and its eyes dark brown. Half of the young bird's bill is dark, and the feet are a dull yellow. The full adult plumage probably takes several years to arrive. As with most birds of prey, the female is the larger sex.

Habitat and range

This eagle stays near large open water for most of the year. It uses sea coasts, estuaries, big lakes, rivers, marshes and bogs. It needs old tall trees or good sea cliffs for a nest. In the alluvial wetlands of Croatia, 95 percent of nests sat within 4 kilometres of deep fresh water. Mostly a lowland bird, it still lives at 1,500 to 2,300 metres in Central Asia and Siberia.

Breeding runs from southern Greenland and Iceland east to Hokkaido. Russia is the only country that holds the bird across one huge unbroken area. Norway holds the largest population in Europe, along its coast. Eagles in the west of the range hardly migrate at all. Young birds wander furthest, and one German bird turned up 1,520 kilometres away in France. Over 500 birds winter in Japan, most of them in Hokkaido.

Diet and hunting

Fish and water birds carry this eagle through the year. Nearly 70 kinds of fish and about 170 kinds of bird appear in its prey lists. It prefers fish between 30 and 60 centimetres long, which pay best for the effort. Most prey items weigh between 0.5 and 3 kilograms. It can only take fish in very shallow water, often less than a metre deep.

Now and then a bird plunges into the water from a height of 200 metres or more. A large fish can outweigh the eagle and prove too heavy to lift. The biggest pike taken were put at 12 to 15 kilograms. Captive birds need 500 to 600 grams of food a day, about a tenth of their weight. One male ate an estimated 2 kg at a sitting after he landed a big fish. The eagle also scavenges carcasses and robs other birds of their catch.

Behaviour and social life

A white-tailed eagle spends most of its day sitting still on a tree or a crag. Up to 90 percent of a poor-weather day may pass on one perch. It soars less than a golden eagle does, and it soars mostly over water. A pair roosts together, often close to the nest. Territories run from 52 to 415 square kilometres, and usually stay under 130.

The birds are gregarious where food is heaped, and young birds gather at a carcass. Even so, an adult male that enters an occupied territory can start a serious fight. Two eagles may lock talons, fall and wreck a nest, and one of them can die. In much of Russia the population migrates, unlike most European birds. Juveniles leave their home area by August or September in northwest Europe.

Communication and senses

The species calls a great deal during the breeding season. Some writers find the voice thin for a bird of this size. The male calls a dry krick-krick-krick and the female a deeper krau-krau-krau. A sequence can run to 15 or 30 calls, rising in speed and pitch. Pairs duet in early spring, in the air or from a perch.

An alarm is three or four short loud klee notes. A person near the nest may draw a deep barking call like that of a big gull. Chicks beg with a thin repeated note that grows harder as they wait. A hungry eaglet keeps up a flat monotonous call until a parent feeds it. Like other eagles, it finds prey by sight from a long way off.

Reproduction and life cycle

Pairs stay together for life, though a widowed bird finds a new mate quickly. The season runs from January to July in the south and from April to September in the north. Courtship brings soaring, sky-dancing and loud calling from both birds. The pair may grip talons in mid-air and cartwheel down together. They sometimes break off only a few feet above the ground.

Most nests sit high in a big tree, and cliff nests dominate where trees are scarce. Of 98 Norwegian eyries only eight stood in trees. German tree nests ranged from 8 to 30 metres up and averaged 20 m. A clutch usually holds two eggs, and three or four are rare. A fresh egg weighs 120 to 148 grams. Incubation lasts 38 to 42 days, and the female does 80 to 90 percent of it.

A hatchling weighs about 90 to 100 grams and wears creamy white down. First feathers push through the down at about 30 days. The eaglet feeds itself in the nest from 35 to 40 days old. It tries its first flight at about 70 days and flies well by about 90 days. The mean brood across many studies was 1.52 chicks. A bird that reaches adulthood lives about 21 years, and the oldest known reached 37.

Predators and threats

A grown eagle probably has no natural predator, though the nest is another matter. Red foxes, martens and bears rob accessible nests of eggs and chicks. Wild boars eat eggs and chicks that fall from the nest. Crows, ravens and marsh harriers take eggs when the parents are away. Eurasian eagle owls have killed fairly large nestlings at night.

About a third of nesting attempts raise nothing at all. Starvation and nest collapse kill more chicks than any predator. The larger chick sometimes kills the smaller one, though that is rare in this species. Shooting, poisoning and power lines still kill grown eagles. Turbines at the Smola wind farm in Norway killed 36 birds between 2005 and 2010.

Population and conservation

The bird once bred across western Europe and south to the Mediterranean. Persecution ran from the early 1800s to the Second World War. Britain lost the species by the early 1900s, and the last nest failed on Skye in 1916. Pesticides then broke eggshells across the surviving range from the 1950s. In the 1970s, 56 percent of ringed young in the Nordic countries and Greenland were found dead. Most of those had been shot.

Protection appears to have changed the picture within a generation. Sweden put clean carcasses out in winter, and breeding success rose from 29 to 44 percent. Poland preserves a group of trees around every eyrie in its state forests. Russia held 5,000 to 7,000 pairs in the late 1990s, with about 3,500 pairs in Europe. The IUCN lists the species as Least Concern. France and Israel still class it as Critically Endangered inside their borders.

Relationship with humans

Shepherds and gamekeepers once treated the eagle as a rival for their stock. The charge against sheep was largely false, but the law backed the killers. Britain paid a bounty of five shillings a head by about 1700. Coastal nests were easy to reach, so egg collectors emptied them for sale. Trappers hid in a pit, baited an eagle with carrion and seized it by the leg.

Reintroduction reversed the loss in Britain. Workers released 82 Norwegian birds on the isle of Rum between 1975 and 1987. Fifteen more chicks went to a site in Fife in 2008. England had breeding birds again in 2019, and the Netherlands from 2006. The Dutch population reached 20 breeding pairs by 2020. Eagle watching now seems to draw many visitors to the Scottish islands.

In culture and myth

People in Orkney placed sea eagle bones in a Neolithic cairn on South Ronaldsay. The site is known as the Tomb of the Eagles, and the cairn dates from about 3200 BC. The bird bones are much younger, from about 2450 to 2050 BC. That gap weakens the old reading of the eagle as a totem of the people buried there. Pictish carvers on Orkney cut sea eagles into stone as well.

Cut marks on eagle talons at Krapina suggest that Neanderthals wore them as jewellery. Saxon art and story gave the bird a large place, and many landmarks carry its name. Heralds often draw a sea eagle holding a pike, which separates it from other eagles. The white eagle of the Polish coat of arms is thought to be this species. In the legend, Lech found a white eagle on its nest and built Gniezno on the spot.

Fishermen in Shetland held that fish rose belly up when a sea eagle appeared. Some of them smeared eagle fat on their bait to bring a bigger catch. Gaelic keeps a name that ties the bird to the eye of the sun.