When Do Dunlins Spend High Tide in Flight?

Abstract

-In intertidal habitats, Dunlins (Calidris alpina), like other shorebirds, spend 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 coast and try to analyze factors associated with this behavior. Over-sea flocking occurred at only one site, the Jadebusen, where it was recorded on 5 out of 35 occasions. Over-sea flocking was associated 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, suggesting that over-sea flocking is a reaction of Dunlins to high risks of surprise attacks by raptors. Received 20 March 2000, accepted 8 May 2000.