Wing-spreading, wing-drying and food-warming in great cormorants Phalacrocorax carbo

Wing-spreading of cormorants (Phalacrocoracidae) is a characteristic and enigmatic aspect of their behavioural repertoire. It has been suggested to have a range of functions including wing-drying, food-warming, and social signalling of foraging success. We investigated two of these putative roles by comparing the wing-spreading behaviour of fed and unfed animals after they had been swimming and diving. The duration of wing-spreading was correlated only with time spent on the water. The ingestion of food did not influence the duration of wing-spreading, a finding that supports a wing-drying, rather than a food-warming, function.