Moulting eiders normally gather in shallow waters along the coast, thus coming into conflict with recreational boat use. Researchers from the Norwegian Institute for Nature Research (NINA) and the Norwegian University of Science and Technology (NTNU) in Trondheim have, for the first time, investigated the escape behaviour of moulting common eiders when approached by small motor boats.

Experimental boat approach

When moulting in late summer, common eiders rely on shallow coastal areas to find sufficient food for this energy-demanding process. However, these same areas are also very popular among recreational boat users in the same period. In an experimental study on the coast of Møre and Romsdal, flocks of moulting common eiders were approached by a small motor boat at a comparatively low speed of 6 knots. The behaviour of the ducks was recorded prior to approaching them, during the approach and afterwards.

Increasing escape response

Common eiders started to show signs of disturbance at a flock-to-boat distance of 700 m, and at first started to swim away from the boat. When the boat came closer, the eiders started to swim underwater, and finally escaped on the surface while flapping wings at an average distance of 177 m. Despite being mostly flightless, birds moved on average 771 m from their original location. Most flocks started to forage or rest again within 10 minutes of the disturbance, but a few flocks kept swimming away and showed signs of disturbance reaction more than 45 minutes later. Finally, common eider flocks moved into deeper water after disturbance than where they were prior to being approached by the boat.

When moulting, common eiders lose their flight feathers and become flightless. They often move into shallow areas in search for energy-rich food.
Photo: Nina Dehnhard

Need for more awareness

The results of this study suggest that approaching boats may cause considerable disturbance effects for moulting common eiders through increased locomotion costs, displacement from preferred foraging habitat and/or time lost for foraging or resting. Earlier studies have shown that conditions during the moult season may also impact the productivity in the following breeding season. This study highlights the need for awareness among boat drivers on potential consequences of their presence and the need for respectful behaviour towards wildlife in their natural habitats.

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Contact person: Nina Dehnhard, NINA