Disturbance of Non-Breeding Waders by Pedestrians and Boats in a Mediterranean Lagoon

Flight initiation distances (FIDs) were measured for nine wader species at the Venice lagoon (Italy), one of the most important sites for waterbirds around the Mediterranean. The response (277 instances) to boat and pedestrian disturbances caused outside the breeding season was observed. FID was positively and significantly correlated with the mean body size of the species. The correlation between FID and flock size was also positive and significant, irrespective of the type of disturbance. FID values ranged from 27.9 + 15.6 m (mean + SD, N = 32) in Common Snipe to 140.4 + 48.1 m (N = 30) in Eurasian Curlew, pooling data for both disturbance types. The same ranking was observed if pedestrian and boat disturbances were considered separately; differences were species-specific. For six species, the data allowed comparisons to be made between boat- and pedestrian-evoked FID; the observed differences were not significant. Thus, boat disturbances during the non-breeding season did not evoke a stronger response among waders, in terms of FID, compared to pedestrians. According to these results, set-back distances, expressed as mean FID + 2 SD, are suggested to reduce the effects of man-made disturbances to waterbirds at a local scale. These distances range from 59-74 m for the most confiding species (Common Snipe, Kentish Plover and Ruddy Turnstone) to 121–267 m for the most wary (Eurasian Oystercatcher, Grey Plover and Eurasian Curlew). To protect the multi-specific and often large winter roosts from disturbance caused by pedestrians or boats, a higher set-back distance, 270 m, is suggested. —Scarton, F. (2018). Disturbance of non-breeding waders by pedestrians and boats in a Mediterranean lagoon. Ardeola, 65: 209–220.