German Federal Agency for Nature Conservation (BfN)


Breeding success among common mergansers on Vilm

Breeding success among common mergansers on Vilm

Photo: Ralf Grunewald
Gänsesägerfamilie Foto: Ralf Grunewald

Vilm, 18.05.2017 This May a recent breeding success among common mergansers (Mergus merganser) has been observed in the shallow waters around the Isle of Vilm, which is a rare event since the late 1980s.

 While in 1981 approximately twelve breeding pairs were counted in hollow trees and nesting boxes on Vilm [1], breeding or breeding success was not monitored in following years; however, a few pairs continued to breed on the island and small chicks were sighted from time to time. Generally common mergansers visit the island and its surrounding waters mostly as winter guests. Towards the end of winter most of the birds migrate back to Sweden, where they spend the breeding season. During recent years remnants of clutches destroyed by martens (eggshells) have been found on the circular path.

The ancient and since almost 500 years hardly untouched forest of Vilm offers perfect breeding conditions for the big aquatic birds. They need old trees with large, cavities close to the shore, because they primarily breed in hollow trunks, thus only martens are able to prey on them. As soon as the chicks hatch, they jump out of the breeding burrow into the depth and use their small wings as sails. Since the chicks are not able to fly by that time, uncountable perils lie along the way to the water, hence this distance should be rather short. Only few landscapes in Germany remain offering the combination of ancient trees in close proximity to the coast.

[1] L. Jeschke, G. Klafs & H. Schmidt, Das Naturschutzgebiet Insel Vilm, Ostsee-Druck Rostock, Betriebsteil Putbus, Broschüre, o.J. (vermutlich 1980er Jahre)