Sharing waters: the impact of recreational kayaking on moulting mute swans Cygnus olor

Coastal waters of northwest Europe have recently been subject to growing recreational human activity, which may invoke a parallel upsurge in the associated disturbance-related impacts on coastal habitats and wildlife. In this study, we investigate the effects of recreational kayaking on moulting mute swans (Cygnus olor) in a Danish fjord, by carrying out controlled disturbance events in a natural setting, and combining drone technology and land-based observations to allow for multiple perspectives on the birds' response. The distance at which the swans began to swim away from the approaching kayak (the escape distance) averaged 297 m, and the swans were covering an average distance of 376 m (displacement distance), while swimming for a mean of 8 min and 40 s. The danger perceived by the moulting swans (assumed to be reflected in their speed of locomotion) was negatively related to the distance to the kayak, and was greatly influenced by its heading, being most intrusive when birds were approached head-on. In comparison to undisturbed birds, disturbance by a kayak substantially increased locomotory behaviour, and led to lower proportions of foraging both during and after the disturbance event. Our data indicate that energy expenditure was approximately 34% higher during passage of a kayak than prior to disturbance. The results suggest that the effects of recreational kayaking on moulting swans can be minimized by keeping a distance of > 300 m, avoid sailing directly towards swans, and by avoiding kayaking in sheltered bays with shallow water.