in today's issue of one of Finland's leading newspapers Turun Sanomat
(July 1st, http://www.ts.fi/uutiset/kotimaa/363516 ... ruokaloita
) there's a fairly large article titled "Mobs of young white-tailed sea eagles terrorize effectively nestings of cormorant colonies
". it reports that WTEs, especially packs of half a dozen to about a dozen of non-nesting pre-adults have adopted the habit of harvesting colonies of cormorants so that they have been able to ruin their nesting. "Cormorant islets have turned into fast-food restaurants for WTEs within few years.
in the picture in Turun Sanomat the remains of a cormorant after a WTE has had its meal.
besides non-nesting pre-adults also an increasing number of nesting adult pairs of WTEs have been observed to choose their nest sites close to cormorant colonies. "For example in Rymättylä WTEs have built 6 new nests near two large cormorant colonies within 10 last past years
" says special investigator Jouko Högmander from the Finnish Board of Forestry. (or something like that, they did not have an official English name on their website)
the article continues: even though the parent WTEs feeding their young manage to reduce the numbers of cormorants effectively, the largest damage to their numbers is caused by the mobs of young eagles loitering about the cormorants islets for a long time. when eagles land on the islands the cormorant parent flee in panic and then the unguarded nests will be a set dinner table for for the numerous egg thieves in the bird world. "Herring gulls and seagulls will rush in large numbers to break and eat eggs and hooded crows will join in the feast.
", says Pekka Rusanen, an investigator from the Finland’s environmental administration. "The co-operation of WTEs and eggthieves brings about destruction on the cormorant islets. If the nesting is developped far enough, the cormorants will not have time to recover their nesting that season
[by laying a replacement clutch]." says Rusanen.
a few ago researches believed that the change in the feeding habits of WTEs might even stop the increase of cormorant population in the Archipelagic region. Högmander says that he does not anymore believe it will be so, because cormorants are so efficient breeders, though the WTEs may have a restraining effect. populations of cormorants are still increasing at an annual rate of 20 %. the increase is expected to cease within 10 years, when there will be no places for new colonies. this has been the development in Sweden, says Rusanen.