Are Mute Swans (Cygnus olor) really limiting fishpond use by waterbirds in the Dombes, Eastern France

Abstract

The Mute Swan (Cygnus olor) is a protected species whose population has shown a dramatic demographic expansion over the last decades in France. Today, Mute Swans are suspected of causing damages to wetlands, partly through their territorial behaviour towards other waterbirds. The behaviour of Mute Swan pairs and the distribution of other waterbirds was monitored over 84 fishponds in the Dombes, Eastern France, from April to July 2008. Interspecific aggressive behaviours by Mute Swan pairs were not detected during behavioural observations, and no negative impact of swan pair presence was demonstrated on waterbird distribution. Waterbirds were more abundant on fishponds where Mute Swan pairs were present, maybe due to the flocking of waterbirds where Mute Swans were established owing to shared habitat preferences. Indeed, the waterbirds whose presence was the most closely correlated to that of Mute Swan pairs were Coot (Fulica atra), Common Pochard (Aythya ferina) and Red-Crested Pochard (Netta rufina), all foraging on deep macrophyte beds as do the swans. All these species, including swans, may therefore be attracted to the same fishponds without massive interspecific competition occurring, due to abundant submerged aquatic vegetation resources.