The commensal association of waterfowl with foraging swans (Cygnus spp.) was studied in southernmost Sweden. Among more than 1,500 Mute Swans (C. olor) only 2.6% had attending waterfowl whereas 41% of Whooper Swans (C. cygnus) and 51% of Tundra Swans (C. columbianus bewicki) had associated commensals, no doubt because of the species’ different feeding techniques. Four species of commensals occurred at the main study site, Eurasian Wigeon (Anas penelope), Mallard (A. platyrhynchos), Pochard (Aythya ferina) and Common Coot (Fulica atra), wigeon making up about a third of the individuals. A mean of 3.4 waterfowl attended each Whooper Swan. Aggression was common among the commensals, with intraspecific aggression being more common than interspecific aggression in both wigeon and Pochard, and apparently influenced the size and composition of the groups and also the individuals’ positions relative to the swan. The preferred position just behind the swan was defended by threats and attacks. Although wigeon in this position did not have higher pecking rates they obtained significantly more large items than wigeon farther behind the swan.
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Vol. 28 • No. 3