Effects of mute swans on wetlands: a synthesis
The increases in mute swan (Cygnus olor Gmelin) population size have caused concern among stakeholders, who sometimes consider it as a pest species. Here, we aim to review existing studies on the ecological effects that mute swans have on wetlands. Claim that mute swans threaten other waterbirds were partly supported: mute swans sometimes behave territorially towards conspecifics and other waterbird species, but this does not systematically occur. A second common claim, that mute swans damage aquatic plant beds, was upheld in that the species did indeed affect aquatic plant communities in several studies. However, grazing by mute swans does not systematically have negative effects on aquatic plants. Habitat patch size, distance between habitat patches, resource availability and water velocity affect habitat selection process by mute swans, with varying effects depending on season and mute swan breeding status. Scientific knowledge does not support the idea that mute swan population increase can be considered as a biological invasion in Europe. Conversely, there is a genuine risk of biological invasion in North America. In light of the literature review, we discuss the relevance of mute swan population management in Europe and in North America, and propose future research avenues.
KeywordsMute swan (Cygnus olor Gmelin) Population increase Community Herbivory Habitat selection
We thank the organizers of EPCN 2012 for giving us the opportunity to present a summary lecture on the consequences of mute swan for pond ecosystems, which eventually ended up being the present paper. We thank Eileen Rees for helping us to improve the English of the manuscript. We thank the editors and three anonymous referees for valuable comments on an earlier version of the manuscript.
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