Effects of recreational disturbance on tidal wetlands: supporting the importance of undisturbed roosting sites for waterbird conservation

In coastal wetlands, the increasing level of disturbance from recreational activities could threaten waterbird populations, which overall are showing decreasing trends. Despite the crucial contribution of waterbirds to biodiversity, empirical studies measuring the effects of disturbance on them remain scarce, especially in terms of the impact upon their roosting sites. We developed an experimental treatment to measure the effects of a pedestrian walking on a site used by overwintering waterbirds in a wetland of international importance. We registered 156 events (88 at high tide) of flushing birds, totaling 4,018 individuals. Each treatment drove the flushing of 1?C5?% of the wintering populations of nearly all species present during high tide. In addition, 1.5?% of the Eurasian curlew wintering population was driven to change site. All the effects were found to be reduced during other tidal periods. Therefore, allowing recreational use in a previously undisturbed area can systematically increase daily energy expenditure of significant percentages of different waterbird populations during high tide, and even cause birds to avoid a site completely. These effects will probably be even worse given that our results were derived only from a disturbance source of low magnitude and frequency. We recommend that, prior to developing recreational areas close to the shoreline, coastal wetland managers should study the habitat use of waterbirds during high tide in relation to total waterbird populations using the wetland.