About the species

The sea eagle is our biggest bird of prey. The heaviest recorded individual weighed 8 kg. The biggest recorded individual had a wingspan of 2.65 metres. Females are considerably larger than males (approx. 2kg), but large males may be as big as small females.

Sexually mature sea eagles have light, grey-brown dappled plumage, lightest at the head and neck, darkest below. The tail is white and the beak is massive and yellowish-white in colour. Their first plumage is a dark, saturated brown colour with large, black-brown wing feathers, and the head and beak are dark. The back and breast plumage has a regular, speckled pattern. There may also be yellowish-white markings on the tail and underside of the wings.

The young have similar sized bodies to adult birds, but their wing and tail feathers are longer and they may therefore appear larger when in flight. Over the next two years, the sea eagle's plumage becomes a darker brown, with a considerable amount of white speckles. At the age of 4 or 5, the juvenile plumage gradually transforms into adult plumage and the birds become sexually mature, even though they do not normally nest at such an early age.

Roaming

Sea eagles are non-migratory birds, but juveniles will often roam during their first 3 or 4 years of life. They may then congregate in quite large flocks, and up to 80 individuals have been recorded together in Bodø. Roaming juveniles from Norway have been recorded all the way down to the Netherlands. Sea eagles from Sweden, Finland and the Baltic countries spend the winter along the Norwegian coast.

Feeding Habits

Sea eagles are more closely related to vultures than to our other birds of prey, resembling them in both behaviour and appearance. Recent studies show that the diet of most sea eagles consist of at least 80-90% fish. In addition to fish, they also consume substantial amounts of sea birds and water fowl, and depending on the time of year, a considerable amount of carrion. There is a lot of evidence to suggest that sea eagles are far less adept hunters than was previously believed, and that perhaps most of their diet consists of carrion, is stolen from others, or has been found as the remains of the meals of other species. Sea eagles often depend on "good helpers": Otters that leave food behind, gulls or other birds that the sea eagle can steal from, people who discard fish or other waste after a fishing trip.

The daily nutritional need of an adult sea eagle is about 300g of digested food. They normally eat between 500g and 1 kg at each meal, sometimes almost 2 kg. Therefore, an adult sea eagle will normally eat every second or third day. Growing juveniles will require a little more.

Sea eagles are far from being "freighter aircraft". It has been confirmed that they can lift and carry away prey weighing just over 3 kilos, but as a rule they do not try to carry off prey weighing more than 2 kilos.

Nesting sites

Whenever possible, sea eagles prefer to nest in trees, particularly pine trees, but otherwise any that are available. This will often mean aspen or birch. If there are no big trees available, they will nest at the foot of a tree in very steep terrain.

In areas with no trees they will choose ledges and shelves on precipitous cliff faces. If there are no trees or cliffs, they will nest on the ground, near an escarpment, on a hilltop or on a flat surface.

The nests are often used for several generations and from century to century. They are built of branches and twigs and are lined with peat, moss and grass. They are often extended from year to year, and can be up to 5 metres in height and weigh 1.5 to 2 tonnes. When built on the ground or on rock ledges, they may only be built of moss and grass.

Sea eagles are monogamous and usually stay with the same partner for their entire lives. In new areas they form pairs at the age of 4 or 5, in some exceptional cases at 3 years of age, and some not before they are 6 or older.

A newly formed pair in a new area will often not build a nest until their second year together, and may not produce young until their fourth year. Although in cases where a new mate replaces an old one, they may be successful in their first year.

Sea eagles normally lay 2 or 3 eggs. In certain cases two females may have the same mate, either laying eggs in the same nest or in their own separate nests. Every year fifty percent of sea eagle pairs nest unsuccessfully.

Sea Eagle Chicks

The chicks are covered in white down when hatched, but soon grow a thick, grey-brown teddy bear-like furry coat. Their proper plumage develops between the ages of 4 and 8 weeks. The young are fledged after 10-12 weeks, males before females.

In just less than half of all clutches, two of the chicks grow to be fully fledged, in rare cases three. The young are fed until late autumn, some follow their parents all winter long. Nesting sea eagles often accept the presence of one-year old juveniles in the nesting area, sometimes even at the nest itself.

Sea eagles have always appealed to people, and have often been conceived of as a symbol of strength and vigilance. They have held an important place in many cultures and been used in coats of arms and emblems.

In more recent times, sea eagles were seen as vermin in large parts of their habitat, and were subject to persecution in the same way as other birds of prey and predators. This led to the eradication of the species in many countries and significant decline in other areas.

Intruders and other threats

In parts of their habitat, sea eagles have also proven very vulnerable to environmental pollutants spread by man. This has led to an increase in mortality rates and a reduction in fertility. In most countries sea eagles were protected early in the 1900's, in Norway not until 1968.

If they have the option, sea eagles prefer to live far away from human settlement, and they always seek out sites where they can nest without interference from human beings.

Intruders can pose a serious problem to nesting sea eagles, halving their chances of success. In the long run, increased human activity in the vicinity of sea eagle nesting sites therefore poses a general threat towards the stock.

Further information

Read more about sea eagles at the Norwegian Ornithological Society's website.