Recolonization of breeding waterfowl communities by the whooper swan: vacant niches available
Breeding population of the whooper swan Cygnus cygnus has increased dramatically in Finland during the last 50 yr, from ca 15 to 1500 pairs. We studied if the recent recolonization by the whooper swan into waterfowl communities in Finland has had negative effects on Anas species belonging to the same foraging guild. Using data of foraging behaviour and ecomorphology of the whooper swan and Anas species, we studied the position of the former in the dabbling guild. We used long-term duck census data from different parts of Finland to study changes in breeding numbers of Anas species in lakes that have been recently colonized by the whooper swan and in control lakes that have not been colonized. Overall, foraging and ecomorphological similarity between the whooper swan and the other species decreased in the following order: pintail A. acuta (most similar), mallard A. platyrhynchos, shoveler A. clypeata, garganey A. querquedula, wigeon A. penelope, teal A. crecca (least similar). We did not find evidence of adverse impact by the whooper swan colonization on population densities of the other species. Neither did we find any indication that species relatively more similar with the whooper swan in terms of foraging ecology would show relatively more negative response to the whooper swan colonization. Our results suggest that whooper swans have occupied vacant niche space when colonizing boreal waterfowl communities.
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Document Type: Original Article
Publication date: June 1, 2000