White-tailed or sea eagle

Autor: Magda Zadrąg    

When looking at the white-tailed eagle it is little wonder that our ancestors chose it as our national symbol, our emblem. Although the white-tailed eagle as a system does not belong to eagles, but to other steller’s sea eagles, it fascinates with its royal and majestic appearance. Not many people know that this incredible predator can be found even in Warsaw. Especially in winter when waters in lakes and smaller reservoirs freeze over, and ducks being the white-tailed eagle’s food, they move to open waters of the Vistula in Warsaw in search of food.
In Poland in the 19th and 20th centuries white-tailed eagles were on the brink of extinction. They were oppressed and exterminated, and also the pesticides used in agriculture did not agree with them. Pesticides, particularly DDT, caused calcium disorders in the birds, hence the eggs they lay could not properly develop due the weak shells. In the 1990s in Poland there were 180-200 pairs of the breeding birds, but thanks to protection, according to the Eagle Conservation Committee currently the numbers of these species increased to 1,000-1,400 breeding pairs.

Identification
The white-tailed eagle is the biggest among the birds of prey, their wingspan is 190-240 cm. In flight it has distinctive long and very wide “finger-like” wings and fairly short, wedge-shaped tail. The bird flies actively, alternating strong deep wing-beats with short periods of gliding. An adult white-tailed eagle is brown with a distinctly lighter golden brown head and neck, huge golden bill and pure white tail. Some top coverings on the body have lighter coloured edges, hence the animal’s back is scaly. The birds do not acquire their adult colouration until they reach 5 years of age, but they can begin mating at the age of 4. In the year that it leaves the nest the white-tailed eagle is markedly darker, plumage is dark brown, and only the centre of the wings are lighter, the bill is also markedly darker than in an adult bird, and it is only yellow at the base. In following years the bird gradually changes individual feathers, until it gets the final plumage.

Young white-tailed eagle. Photo Marcin Łukawski

Young white-tailed eagle. Photo Marcin Łukawski

Adult white-tailed eagle. Photo Marcin Łukawski

Adult white-tailed eagle. Photo Marcin Łukawski

The white-tailed eagle’s year
Adult white-tailed eagles stay in pairs in their territory all year, although in winter they may move in search of food. They occupy old tree stands most often in river valleys or nearby other water reservoirs, such as lakes or ponds. The pair protects only its closest area from other white-tailed eagles, but tolerates other birds on feeding grounds.

White-tailed eagles mate intensively in January and February. Mating takes place in the air and is very impressive. The male and female join in flight by their claws and fall together, separating only just above the ground. Additionally, the birds make mating cries. At the same time the pair rebuilds the nest. The nest is made on a big, old tree and is of a big construction, it can be up to 4 m in height and 2.5 m in diameter.

The female lays 2-3 eggs in March and incubates it for 38 days. During that time the male feeds the female, and sometimes, although not infrequently, the male takes over the incubating. Because the female starts to incubate eggs from the moment the first is laid, chicks are hatched asynchronously – the age difference between the chicks maybe 2-3 days.

Over the next 10-11 weeks chicks remain in the nest and are fed by the parents and protected by them. At first the young are covered with thick, cream-coloured down feathers and are still kept warm by their parents. At the age of about 3 weeks a second layer of down feathers starts to grow – darker in colour and from that moment whey can remain in the nest on their own. Contour feathers grow on the young between the fourth and eighth week of age.

After leaving the nest the chicks are fed by their parents for the next 5-6 weeks and they stay in the area until September. During the first years of their life they live alone, moving from place to place in search of food.

White-tailed eagles prey primarily on fish and water birds, coots, ducks and grebes. They also do not scorn carrion, around which several can be observed together. During preying the white-tailed eagle primarily uses its sight. Its eyes are about twice as large as that of adults, so that its vision is much sharper than ours.

White-tailed gulls require a lot of practice to catch fish as well as water birds. These birds spend quite a lot of time learning to prey efficiently, that is why especially young birds often gather in places where it is easy to get food.

Photo Marcin Łukawski

Photo Marcin Łukawski

Threats and protection
In the past, the white-tailed eagle became almost completely extinct in Poland as primarily they were oppressed and were fired at, as well as poisoning of the environment with pesticides, including DDT. White-tailed eagles were shot at, and even today this still occurs sometimes, as it is considered to be a bird destroying fish farms. Another threat to white-tailed eagles was an overly intensive forest management and the cutting down of old trees.

These threats have been addressed – shooting at white-tailed eagles is prohibited by law, also DDT is no longer used in agriculture and a protection zone for nests of these birds has been introduced. The protection zone prohibits the conduct of forest management throughout the year within a 200-metre radius from a nest that has been found, and within a 500 metre radius from 1 January to 31 July. This ensures that the birds maintain their nesting places, that there is an appropriate number of old trees, and also peaceful surrounds when rearing the young.

Probably due to this type of protection we can observe a marked increase in white-tailed eagle population in the country. However, the white-tailed eagle is still in danger of poisoning and collisions: most often with overhead electrical lines, and sometimes also with trains. In some places intensified tourism also has a bearing. Therefore, it is t important to take into account white-tailed eagle’s neighbourhood especially when planning new infrastructure investments.

Literature:
Cenian Z., Lontkowski J., Mizera T., Wzrost liczebności i ekspansja terytorialna bielika Haliaeetus albicilla jako przykład skutecznej ochrony gatunku. Studia i Materiały Centrum Edukacji Przyrodniczo Leśnej. R. 8, 2(12), 2006.
Chylarecki P., Sikora A., Cenian Z., (red.): Monitoring ptaków lęgowych . Poradnik metodyczny dotyczący gatunków chronionych Dyrektywą Ptasią. Warszawa, GIOŚ, 2009.
Svensson L., Ptaki Europy i obszaru śródziemnomorskiego, Multico Oficyna Wydawnicza, 2011.Tomiałojć L., Stawarczyk T.: Awifauna Polski. Rozmieszczenie, liczebność i zmiany. Wrocław. Wyd. PTPP „pro Natura”, 2003.
Volponi P.: Bielik – Król polskich ptaków. Życie herbowego ptaka Polski w końcu XX wieku. Faenza, Edit Faenza, 1998.

The project ‘Protecting the habitats of priority bird species of the Vistula Valley under conditions of intensive pressure of the Warsaw agglomeration’ (wislawarszawska.pl) has received a grant from the Financial Instrument for the Environment (LIFE+) and from the National Fund for Environmental Protection and Water Management.