The White Tailed Sea Eagles of Kenmare Bay
The White-tailed Sea Eagle is the fourth largest eagle in the world! Measuring up to 0.94m in length with a wingspan of up to 2.45 m (8 ft) which is the largest wingspan of any eagle, and is on average the fourth heaviest eagle in the world, the largest known specimen weighing approximately 17lb.
The White Tailed Sea Eagle has broad “barn door” wings, a large head and a large thick beak. The adult is mainly greyish-brown except for the slightly paler head and neck, blackish flight feathers, and distinctive white tail. All bare parts are yellow in colour, including both the bill and the legs. In juvenile birds, the tail and bill are darker, with the tail becoming white with a dark terminal band in sub-adults. The combination of mousy-brown colouration, broad, evenly-held wings, white tail, strong yellow bill and overall large size render the White-tailed Eagle essentially unmistakable in its native range.
Some individuals have been found to live over 25 years, 21 years being the average.
The White-tailed Eagle’s diet is varied, opportunistic and seasonal. Prey can often include fish, birds and mammals. Many Sea Eagles live largely as scavengers, regularly pirating food from otters and other sea birds including cormorants, gulls, Ospreys and various other birds of prey. Carrion (flesh of deceased animals) is often the primary food source during lean winter months, with fish and ungulates being preferred but everything from marine mammals to livestock to even humans being eaten after death. However, this eagle can be a powerful hunter as well. The daily food requirement for a White-tailed Eagle is in range of 500–600 g. Although generally a less active hunter than the Golden Eagle, competition over food can go either way, depending on the individual eagle. They can exist at higher population densities and typically outnumber Golden Eagles because of their longer gut and more efficient digestive system, being able to live better with less food.
Virtually any fish found near the surface is potential prey for the White-tailed Sea Eagle. Commercial fisheries and carp ponds are readily exploited by the eagles when available. Although they occasionally kill and harass some land birds, White-tailed eagles usually target water-based birds as prey including loons, grebes, ducks, coots, auks, gulls, geese and even swans have been preyed upon. Adults, nestlings and eggs of other birds are all regularly consumed. When targeting non-nesting birds, they often fly towards a waterbird repeatedly, forcing it to dive again and again, until the bird is exhausted and more easily caught. When very large prey is killed, such as swans, the prey may be dragged along the surface of the water to the shore to be consumed. Live mammals consumed have ranged in size from voles to lambs and deer calves, the latter likely around the same size as the record-sized deer flown with by Bald Eagles in North America.
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 a 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 nest. 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; one nest in Iceland has been in use for over 150 years. In Scandinavia, trees have been known to collapse under the weight of enormous, long established nests.
The territory of the White-tailed Sea 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. In adulthood the White-tailed Eagle has no natural predators and is considered an apex predator.
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.
Surplus chicks are sometimes removed from nests to use in reintroduction programs in areas where the species has died out. If left in the nest, they are often killed by the first-hatched sooner or later, as in most large eagles.
In such programs the birds are raised in boxes on platforms in the tree canopy and fed in such a way that they cannot see the person supplying their food, until they are old enough to fly and thus find their own food.
Near-Extinction and recovery in Europe
White-tailed Sea Eagles are apex predators. Therefore, they tend to experience bioaccumulation from environmental pollutants that are present in their prey, and also suffered intensive persecution by shepherds and gamekeepers who considered them (usually wrongly) to be a threat to their livestock and gamebirds. During the period 1800-1970, White-tailed Sea Eagles in most of Europe underwent dramatic declines and became extinct in many regions of western, central, and southern Europe. While Norway, Germany, Poland, and Iceland harboured the largest surviving populations, pockets of reproducing pairs remained in several other countries. Intense conservation actions throughout much of the remaining European distribution range (legal protection to decrease hunting, protection of breeding sites, and winter feeding) led to a recovery of many local populations. Since the 1980s, the European White-tailed Eagle population has recovered steadily, and is spreading back westward. It has today recolonised several traditional breeding areas in Europe and the recovery is still on-going, assisted in Ireland and the United Kingdom by reintroduction schemes.
The White-tailed Sea Eagle is being reintroduced to Ireland where its Irish name of Iolar Mara (sea eagle) reflects its historic association with the long coast of the island. The program started in the summer of 2007. Fifteen to twenty young eagles from Norway are being released each spring into the Killarney National Park in the south-west of Ireland. This comprehensive project will last a number of years with many more eagles being released. The species has a rich history on the island but became extinct in Ireland in the 1900’s due to persecution from landowners. The last pair bred on the coast of Mayo in 1912.
The first White-tailed Sea Eagle breeding pair since 1912 nested 100 years later on Lough Derg (Loch Deirgeirt), marking a great success for the Irish reintroduction programme. In early May 2013, the first eaglets were born in Ireland since the re-introduction programme began; one in the Killarney National Park and two in County Clare.
Studies of DNA in White-tailed Sea Eagles from North-central Europe have shown that the recovering European population has retained appreciable amounts of genetic diversity, implying low risk of inbreeding depression (a serious concern in species with low population density). Therefore, the recovery of this formerly endangered species is a true success story for nature conservation. The story also shows how local protection of a species can be successful and important for preserving the species’ evolutionary potential.