When do Dunlins spend high tide in flight?

In intertidal habitats, Dunlins (Calidris alpina), like other shorebirds, s pend most of the time around high tide roosting on the ground. Occasionally : however, Dunlins remain airborne at high tide and fly over the sea rather than sitting in saltmarshes. Here I describe over-sea flocking in Dunlins on the German Wadden Sea cease and trp to analyze factors associated with t his behavior. Over-sea flocking occurred at only one site, the Jadebusen, w here it was recorded on 5 out of 35 occasions. Over-sea flocking was associ ated with the absence of safe (poorly or non-vegetated) roosting sites, the presence of tall trees close to the site and the presence of raptors, sugg esting that over sea flocking is a reaction of Dunlins to high risks of sur prise attacks by raptors.