The Wilson Bulletin
Author(s): 
Shane P. Mahoney and William Threlfall

Common Murres (Urres aalge) nest colonially and in fact breed at greater densities than almost any other bird species. However, once away from breeding sites they occur singly or in loose aggregations. The social situation during the non-breeding season is quite different from that during breeding, where extreme crowding is possible through the inhibition of intense aggression and escape tendencies. The problems presented by this highly stressful situation (breeding conditions) have been well defined.