Escape distances (EDs) have been used to study sensitivity of waterbirds to different sources of disturbance, to design reserves for waterbirds, and to define eco-targets for the Wadden Sea management plan. However, the use of ED as an index of sensitivity has been criticised because it can be highly variable. Although some factors affecting variation in the EDs of species have been studied, there is still a need for further analysis of factors that may affect it. In this study, we analysed the EDs of 19 waterbird species (geese, ducks, waders and gulls) exposed to a walking person (N = 1,371) during autumn and spring 1980–1984 under controlled conditions in the Danish Wadden Sea. We analysed how EDs varied between species in relation to body mass and hunting and within species in relation to flock size and weather conditions. EDs increased significantly with species body mass, and quarry species (dabbling ducks, curlew Numenius arquata, golden plover Pluvialis apricaria, common gull Larus canus and black-headed gull L. ridibundus) had longer EDs than non-quarry species when corrected for body mass. EDs increased with flock size in dabbling ducks and nine waterbird species in autumn and two waterbird species in spring. In autumn an inverse relationship was found between visibility and ED for dabbling ducks and five wader species. An inverse relationship was also found between wind force and ED for three wader species, but this relationship was found to be positive for two wader species. Several factors affected EDs, and EDs measured in one region may not apply to other regions. Based on our results it is recommended that reserve borders (core area and buffer zones) are designed to take into account mean EDs as well as variation in EDs, with respect to local disturbance levels, flock size and target species.
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Vol. 11 • No. 1