Włodzimierz Meissner
Ornis Polonica 2010, 51: 275–284
https://doi.org/10.12657/ornis.2010.4.3
Abstract: In 2003–2004 a study was conducted aiming to assess the seasonal changes in number and distribution of the three common sea-duck species. The research was carried out on the Baltic Sea between Białogóra and Władysławowo in the two zones: coastal and open-sea zone. Birds were counted from a ship along the same routes. The number of Long-tailed Ducks Clangula hyemalis was the highest in autumn (maximum 42000 ind.), and subsequently declined. The species reached high numbers in both zones. The Common Scoter Melanitta nigra ocurred mostly in coastal zone. Its number fluctuated considerably throughout the season, and reached a peak of 3300 ind. (in both zones) on 5th April 2004. The Velvet Scoter M. fusca was much more abundant in open-sea zone, and reached a peak in autumn (9500 ind.). In autum the highest densities of the ducks were found in a narrow belt of shallow waters of coastal zone, while in winter and spring most birds were concentrated in north-eastern part of the studied area with deeper waters. The most plausible reason for the desertion of coastal-zone was over-exploitation of mussel populations, which constitute the main food of the ducks. Deeper waters in open-sea zone offer high densities of benthic organisms, although diving there is more costly in terms of energy. Changes in the numbers of Long-tailed Ducks could result from both the end of autumn migration and movements of some birds to open-sea zone.
