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.



Trends of wintering populations of the focal species

The wintering populations of all five focal species in the Baltic have reportedly declined between 1987 and 2009 (Skov et al. 2011). The recent results rely on data from surveys performed in 2007–2009, which were compared to data collected in 1992–1993 (Durinck et al. 1994). These surveys aimed at obtaining densities of birds, i.e. to identify the relatively most important areas for each species using land-based counts, aerial total counts, aerial transect counts and ship-based transects. Estimated population sizes from these data were made by integrating density estimates for discrete areas of different density levels. Further, to assess changes in numbers, these were compared with the previous density data created by Durink et al. (1994). Thus, the large-scale decreases of wintering seaducks are based on two large-scale surveys of the birds both producing a total estimate of the population size, which are compared.


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