CLIFF-FACING BEHAVIOR OF THE SWALLOW-TAILED GULL CREAGRUS-FURCATUS

An unusual behavioural characteristic of the cliff-nesting Kittiwake R issa tridactyla is its tendency to face the rock wall behind the nest. New data from the ecologically similar but distantly related Swallow- tailed Gull Creagrus furcatus show a similar tendency to face the rock wall behind the nest, a tendency not shown by the ecologically dissim ilar Herring Gull Larus argentatus when it occasionally nests on cliff s. The comparison suggests that facing the rock evolved as a behaviour al adaptation to nesting on the cliff and is not merely a spatial cons traint. Swallow-tailed Gulls nesting on flat ground near objects face those objects, which suggests that the pronounced tendency of Kittiwak es and Swallow-tailed Gulls to face the rock wall evolved from a gener al preference for facing nearby large objects.