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Trends and drivers of change in diving ducks

image of Trends and drivers of change in diving ducks

This report addresses changes in population size in five species of diving ducks breeding and wintering in the Baltic Sea. Declines in breeding Greater Scaup, Eider and Velvet Scoters on the Baltic coast are verified. Long-tailed Ducks and Eiders have declined in winter. Breeding Eiders have declined in Norway. Monitoring programs in all Nordic countries are partly inadequate for detecting changes in numbers of birds both in winter and during breeding, but large-scale trends appear reliable. The reasons for the declines observed are largely unknown. For breeding Eiders in the northern part of the Baltic Sea a change in predation regimes on the breeding islands may be important. If the negative trends are to be stopped, a deeper understanding of the drivers involved and better knowledge about the ecological status of the Baltic Sea food webs utilized by the diving ducks are needed.

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Introduction

The publication of the report on the population status of waterbirds wintering in the Baltic Sea (Skov et al. 2011, Waterbird Populations and Pressures in the Baltic Sea, TemaNord 2011:550) highlighted a rapid decline in a number of seaduck species wintering in the Baltic Sea, including Greater Scaup (Aythya marila), Common Eider (Somateria mollissima), Long-tailed Duck (Clangula hyemalis), Common Scoter (Melanitta nigra) and Velvet Scoter (M. fusca). While these species are not exclusive examples of declines reported, these seaducks are numerically very dominant among the wintering birds, and all feed mainly on mussels, such as Blue Mussels (Mytilus edulis x M. trossulus). This common feature in the ecology of these ducks, generates a second central question on possible changes in the abundance of their preferred food reflecting changes in the Baltic Sea food chains on a more general level (e.g. Ottwall 2012).

English

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