Europe's biggest eagle

Birds, 15 April 2019
White-tailed eagle (Haliaeetus albicilla)

The white-tailed eagle (Haliaeetus albicilla) has many names.

In Norway and Denmark it's the havørn, in Sweden it's the havsörn, in France the pygargue à queue blanche, in Germany the Seeadler, in Russia the орлан-белохвост, in China the 白尾海雕 and in Japan the オジロワシ.

Most of these names mean "sea eagle". It has special adaptations for catching fish; it can fly very slowly, and its feet have excellent grip, with long talons (claws) and very rough skin.

I like the Gaelic name, "iolar sùil na grèine" or "eagle of the eye of the sun". The white-tailed eagle is an intelligent hunter, and it often comes from out of the sun. In other words, it approaches its prey (the animals it kills) with the sun directly behind it, so that the eagle is invisible until it's very close.

 

 

Size, weight and shape

Comparative size of white-tailed eagle

This is a very big eagle, about 10% bigger than the golden eagle (Aquila chrysaetos) and slightly bigger than its own closest relative, the American bald eagle (Haliaeetus leucocephalus).

There isn't enough data to be sure, but it's possible that the white-tailed eagle's maximum wingspan of 2.45 metres (8 feet) makes it wider than any other eagle in the world.

Some other eagle species are heavier. White-tailed eagles typically weigh 6kg (13 pounds) but they can weigh 7 kg or possibly even 8kg. That's not much for a bird with a 2.45 metre wingspan; it's about the same as a dachshund or a small spaniel.

The white-tailed eagle has broad wings like many other slow-flying birds of prey such as owls, vultures and other eagles. Broad means "relatively wide for their length". The opposite is "narrow".

White-tailed sea eagle underlit

This wing shape is good for:

High lift (so it can take off and land in a small space)
Efficient low-speed soaring
Slow, silent descents

Wing shape of eagle, falcon and swift

The separate primaries (the long feathers like fingers at the tip of the wing) create a lot of additional lift with an aerodynamic "slot effect" and wingtip vortices.

All these features are great at low speeds, for example when you want to fly low over water and catch a fish, but they make high speeds impossible.

Compare with the long, narrow wings of a high-speed bird like the peregrine falcon (Falco peregrinus) or the swift (Apus apus).

 

 

Diet

White-tailed eagles will eat almost any form of animal food, from insects and mice to this dead seal:

White-tailed eagle with dead seal

They need about 600 grammes (1.3 pounds) of meat every day, which is about 10% of their body weight. Worldwide, their diet is 50% birds, 40% fish and 10% small mammals.

Eagles are very light for their size. That means they're fragile. Although they are naturally fierce, they don't want a broken wing so they prefer not to hunt prey animals that could injure them. Eagles and vultures are both scavengers, which means they both eat carrion (fish and other animals that are already dead).

It is said that they sometimes kill adult foxes (Vulpes vulpes) and adult roe deer (Capreolus capreolus). It's possible, but you can't believe all you hear about eagles. It is also said that a white-tailed eagle in Norway once grabbed the dress of a little girl 3½ years old, picked her up and carried her away to its nest, but let her go uninjured. That's a Norwegian myth; a child that age would weigh more than 14 kg (30 lbs),which is too much for a 6kg eagle to carry.

White-tails have very different diets in different parts of the world. In some areas they eat almost entirely fish, such as Arctic char (Salvelinus alpinus) which they catch at sea, in lakes and in wetland areas. In Scotland, they eat a lot of rabbits (Oryctolagus cuniculus) and mountain hares (Lepus timidus).

Worldwide, their favourite food seems to be the pike (Esox lucius). This is a predatory freshwater fish that can be 1.5 metres (5 feet) long, although it's usually much smaller. The pike is also easy to see from the air, because its sides are a light silver-green colour.

Their second favourite food is the mallard or wild duck (Anas platyrhynchos), especially at the end of summer when the mallard is in "eclipse plumage" and can't fly for a month. They also eat young seagulls, they catch eider duck (Somateria mollissima), and they like the common lumpsucker (Cyclopterus lumpus), a spherical fish that lives on the sea bottom. They quite often eat hawks of all sizes.

 

Big trouble for the white-tailed eagle

In the 19th and early 20th centuries, all the white-tailed eagles in Britain and Ireland were killed, either with poison or by shooting. The last one in Britain was shot in 1918, in Scotland. This was done legally. At one time the British government paid 5 shillings for each dead white-tailed eagle, because landowners said that they killed lambs and game animals, which are things like grouse, pheasant and deer that people kill for sport.

The same arguments were used recently by landowners who wanted to stop the reintroduction of these birds to Scotland, and farmers in Ireland today say that eagles kill healthy lambs. Is it true?

Lambs

A lamb is a baby sheep. Domesticated sheep are the result of thousands of years of selective breeding by farmers. They aren't as tough and independent as wild sheep like the mouflon or argali. Modern sheep are more productive, less dangerous and a lot easier to catch, but they're not very intelligent and they need more support from humans.

Lambs dead from neglect

Eagles look quite similar to vultures. They have broad wings, they fly and hunt in similar ways, and their "ecological niches" overlap. They both look for dead or dying animals. An eagle will take a dead lamb, and it will kill a weak lamb that is separated from its mother. If a lamb is separated from its mother before it is weaned, it will die from hunger and hypothermia, with or without eagles and other predators.

There is little or no evidence that white-tailed eagles kill healthy lambs. This would be dangerous for the eagle, because the mother would be nearby. A mother sheep will charge a predator to defend her lamb. From the point of view of an eagle, it is very dangerous to attack a lamb with its mother, but a lamb on its own is an easy meal.

To stay healthy, a lamb must stay with its mother for at least 9 weeks, until it is "weaned" (independent of its mother's milk). With most breeds of sheep, a 9 week old lamb will weigh 16-18 kg, which is too heavy for a 6kg eagle to carry.

With good management, only 5% of lambs will die in their first 9 weeks. Traditionally, every lowland farm had a shepherd who was near the sheep 24 hours per day at lambing time. The shepherd stayed in a "shepherd's hut" on wheels. He or she was ready to make temporary shelters for the sheep, help with a difficult birth, encourage a ewe (female sheep) to be a good mother, and warm up cold lambs. These days, there are not many full-time shepherds in Britain, and "shepherd's huts" are mostly used as artists' studios or for luxury camping. Instead, farms bring the sheep "in-bye" at lambing time. In other words, they put them in a barn (a big agricultural building) or in a field next to the farmhouse, or at least in a field in the bottom of a valley.

However things are different on many hill farms. The parts of the world where a species can survive are called its tolerance range, and these hills are the edge of the range for domestic sheep. There are sheep in Norway, Sweden and Iceland, but they have to live indoors for the whole winter. Sheep find it difficult to survive on the high hills of the British Isles, and the economic model for hill farming means that many lambs never see a human in their first 9 weeks of life. Hill farms may not have any in-bye land for lambs and their mothers.

The high hills of the British Isles get frequent heavy rain, strong wind and low temperatures; there is little or no shelter from trees; the ground is often so wet that sheep get a disease called foot-rot; the terrain is difficult for young lambs; and the high hills have a lot of parasites, especially ticks (Ixodes ricinus, the deer tick or sheep tick) and various blowflies. Tick bites allow infection of joints and organs by Staphylococcus aureus, a condition called tick pyemia which causes weakness, paralysis and death. Blowfly strike or myiasis is when fly larvae ("maggots") start to eat the lamb alive. Maggots of the bluebottle (Calliphora erythrocephala) will eat only dead fles, but the greenbottle (Lucilia sericata) and blackbottle (Phormia terraenovae) will also eat living flesh.

The result is that many lambs get weak; they can't keep up with their mothers. Because they can't walk fast enough, they get no milk, and they quickly die of hypothermia. With or without eagles, about 20% of lambs on British hill farms die during their first 9 weeks of life. One study at Lephinmore (at low altitude on the edge of Loch Fyne) found a 14% "mortality rate" for lambs, and a mortality rate of 25.8% was found in another study over a 6-year period on a hill farm. That means something like a million dead lambs per year on British hills. A report published by the UK's National Sheep Association says lamb mortality can be as high as 90% in some places at some times.

Dead and dying lambs are eaten by crows, foxes and eagles, or they just decay slowly. White-tailed eagles certainly eat dead lambs on hill farms in Britain, and they kill lambs that are separated from their mothers. There is little or no evidence that more lambs die when there are eagles in the area.

 

Game

Game animals are, quite literally, animals that people kill as a game. In other words, it's a sport, a bloodsport. The main game species in Britain are pheasant, grouse, deer, salmon and trout. Shooting and fishing are big business for many "estates" (large areas of land with a single owner) and they provide a lot of employment in areas that have few employment opportunities.

Gamekeeper

My own motto is "take only photographs, leave only footprints", and when I want to enjoy the countryside I go walking, climbing, canyoning, wild swimming or kayaking. However I recognise that shooting and fishing are traditional recreational activities, and that they are economically important in many rural areas.

Still, there are environmental problems with grouse shooting, ethical problems with fox hunting, and I don't think it's possible to justify pheasant shooting, morally or environmentally.

Another problem with shooting birds is that it puts thousands of tons of lead shot (lead, Pb, the toxic heavy metal) into the environment every year.

When sportsmen object to the reintroduction of native species of bird, it's a good time to look closely at what they do themselves. Are they humane (the opposite of cruel)? Are they responsible, or are they damaging the environment they say they protect? Does their sport really create good jobs in rural areas? A YouGov survey in 2018 found that 69% of people in Britain think that shooting birds for sport should be illegal.

 

Better times for eagles

Various images of the white-tailed eagle

The white-tailed eagle has now been reintroduced to the west coast of Scotland. It wasn't easy, and there have been problems with illegal shooting and human egg thieves, but it is a success. If you do a wildlife tour on the Isle of Rum, the Isle of Skye or the Isle of Mull, there's a very good chance you will see them. Of course, if you're a bird there's no need to spend all your time in one place. Since they were first reintroduced on Rum in 1975, they've been seen all over Scotland.

Conflicts between reintroduced eagles and farmers or shooting estates can often be managed by a system for compensation (whether or not the eagles actually cause any financial loss).

There have been some conflicts in Scotland between reintroduced white-tailed eagles and the slightly smaller golden eagle (Aquila chrysaetos). Golden eagles traditionally live in remote mountain areas and eat mainly small mammals; white-tailed eagles traditionally live by the sea and eat mainly birds and fish. Because white-tailed eagles were absent from Scotland for a hundred years, golden eagles moved into their ecological niche. Also, white-tails in Scotland very often eat small mammals. As a result, there has been conflict between the two species, including fights to the death. The golden eagle is smaller, but faster and fiercer, and it is not always the bigger eagle that wins the fight.

White-tailed eagles often catch fish on the surface without getting more than their feet wet, but they also take fish that live on rocks or on the sea bottom, by crashing into the water and then taking off again. There are reports that they will catch a fish too heavy to lift, and take it to the nearest land by "rowing" with their wings. However the white-tailed eagle is less aquatic than the osprey (Pandion haliaetus) which has several adaptations to let it catch fish that are 1 metre (more than 3 feet) under the surface. The osprey has nostrils which close underwater, and waterproof oil for its feathers. If a white-tailed eagle gets wet, it can't fly well, so it has to go and sit somewhere until it is dry again.

White-tails pair for life, and they like to live near water, either the sea or freshwater. They spend nearly all day sitting on some high point, watching. They usually prefer areas with very few people, but in some parts of the world they have got used to commercial fishermen and will even follow them to take dead and injured fish.

Their courtship includes a spectacular display called "talon grappling" or "mutual cartwheeling". Starting high in the sky, they grasp each other's feet and fall together. They don't separate until they're just about to hit the ground.

They don't see well at night, so they are mainly active during the day, and a pair will usually roost (sleep) together at night.

Like most birds of prey, including owls, the white-tailed eagle is often "mobbed" by smaller birds. Seagulls, crows and other birds harass the eagle, both when it is flying and when it is eating. Mobbing an eagle is risky, and the eagle sometimes catches one of the mob.

Very small birds such as tits often choose to live near the nest of a white-tailed eagle, because they get some protection from hawks and falcons.

The eagles either make big nests in trees, or very basic nests on sea cliffs. In their tree nests, they pile up more pieces of wood every year. A tree nest may start off 1 metre in diameter and 2 metres deep, but get bigger every year until it is 2 metres in diameter, 3 metres deep and weighs more than half a ton.

A pair of eagles often has more than one nest in its territory, and it is common for a pair to have five or six nests which they use at different times. The female usually lays either one or two eggs, and there is one brood (one set of chicks) per year.

After a series of reintroductions in Scotland, with young eagles from Norway, they are now breeding successfully on the west coast, on Orkney and on the east coast

Killarney National Park in Ireland is trying to reintroduce the white-tailed eagle. Local sheep farmers protested about this. Since the protest, many of the eagles have since been killed illegally.

 

Listen to the white-tailed eagle

Search for Haliaeetus albicilla on the free online resource Xeno-Canto, and listen to audio recordings of them in Norway, Sweden, Germany and Britain.

 

Picture credits

1: Sea eagle - Boom!! Isle of Mull, Jacob Spinks, Creative Commons BY 2.0
2: White-tailed eagle size diagram, Nicholas of OnePlanet and Linguetic, Creative Commons BY 2.0
3: White-tailed eagle, Raasay, David Evans, Creative Commons BY 2.0
4: White-tailed eagle wing comparisons, Nicholas of OnePlanet and Linguetic, Creative Commons BY 2.0
5: White-tailed eagle with dead seal, Hokkaido, Julie Edgley, Creative Commons BY-SA 2.0
6: White-tailed eagle with fish, Artur Rydzewski Nature Photography, Creative Commons BY 2.0
7: Happy lambs, Nicholas of OnePlanet and Linguetic, Creative Commons BY 2.0
8: Shepherd's hut at Prince Hall, Dartmoor,, Heather Cowper, Creative Commons BY 2.0
9: Dead lamb, Jan Willem Broekema, Creative Commons BY-SA 2.0
10: Dead sheep, Quantocks, Richard Toller, Creative Commons BY-ND 2.0
11: Book cover.
12: Europäischer Seeadler, Andree Kröger, Creative Commons BY 2.0
13:Young eagle above its nest on Littleisland, Norway, Wim Launspach, Creative Commons BY-SA 2.0
14: Wet eagle on beach, Ott Rebane, Creative Commons BY-SA 2.0
15: Talon grappling, Dirk-Jan Van Roest, Creative Commons BY 2.0
16: Eagle mobbed by gulls, Blomsma Fotografie, public domain.