| Summary: | 1. The construction of bottom dwelling offshore wind farms in shallow waters is expected to interfere with seabird feeding and moulting habitats. This study focus on how the disturbance from ship traffic associated with construction and maintenance of offshore wind farms influence moulting common eiders. Such studies might help forming guidelines to minimize potential conflicts between seabirds and the establishment of bottom dwelling offshore wind farms. 2. The study was conducted in coastal areas near the island of Smøla in Møre og Romsdal, Norway, during the moulting period. To simulate the expected increase in ship traffic, flocks of common eiders were approached by boat, while escape responses was observed. 3. Compared to previous studies, there was no differences in the observed flock-to-boat distances regarding initiation of escape responses. The mean flock-to-boat distance for initiating (alert, swimming, diving, flapping/short sprint or flying) an escape responses was 330 ± 146 meters (range 100-700, n=47), whereas the mean flock-to-boat distance when initiating an energy demanding response (diving, flapping/short sprint or flying) was 178 ± 103 meters (range 30-400, n=47). 4. The variance in escape distance was influenced by wind speed and pre-disturbance habitat availability, as both factors caused shorter escape distances for the eider flocks. After 16.5 min 91.8 % of the flocks had returned to the pre-disturbance behaviour.The study did, however, not succeed in addressing important factors for explaining the variance in the time a flock needed to regain pre-disturbance behaviour. 5. Synthesis and applications The results from this study might be used to establish buffer zones towards ship traffic in the vicinity of foraging habitats for moulting common eiders. It is suggested that such buffer zones can be defined by applying the maximum bird-to-boat distances from which the escape responses was induced, with 400 m and 700 m as the least and most conservative, respectively. Applying such buffer zones might be an important step to reduce disturbance of moulting common eiders from ship traffic related to establishment and maintenance of bottom dwelling offshore wind farms, and to make production of green energy greener.
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