Whooper Swans Cygnus cygnus nesting on offshore islands – a new occurrence or a well-forgotten old phenomenon?

Abstract

In recent years, the first cases have been observed of Whooper Swans Cygnus cygnus nesting on the offshore islands and coasts of the eastern Baltic Sea, in Finland and the Leningrad region of Russia. Based both on our own data and a review of the literature, we suggest that the tendency for Whooper Swans to breed on offshore islands was probably the result of the actively growing population having widely colonised the majority of suitable lakes across the continental regions of Finland. This view is supported by Whooper Swans not yet being recorded nesting on Sweden’s numerous coastal islands, where the breeding density of the species is considerably lower. As further supporting evidence, the literature review also found that Whooper Swan nesting in the marine landscape has not been observed anywhere else within its current range. We additionally provide a synthesis of reports made by M.A. Menzbir about Whooper Swans nesting on the northeastern coast of the Caspian Sea in the second half of the 19th century. Based on both historical and current data from other authors, however, we conclude that these claims were in error and that the birds were most likely nesting on coastal freshwater lakes, which were very numerous in the lowlands around the Caspian Sea during the cooler climate conditions of > 100 years ago.