Agonistic Behaviour Among Blue Tits At a Winter Feeding Station

Abstract

Agonistic behaviour in Blue Tits was observed at a feeding station from January 26 to March 15, 1959. The behaviour observed when two birds met at the feeding station was broken down into separate elements to relate behaviour with underlying tendencies to attack, escape, or stay. Encounters between birds were brief and considered instantaneous. The presence of an erect crest and fluffed body feathers was associated with an increased tendency to escape. Facing the rival, horizontal body, erect nape, raised wings, and fanned tail were indicators of an increased attack tendency. An open beak was given largely by an aggressive bird with a strong tendency to stay rather than attack. Maximum probabilities of correctly predicting the outcome of an encounter between two birds by using different combinations of behaviour elements were 0.48 for attack, 0.94 for escape, and 0.79 for staying. Hence much of a bird's motivation to attack or stay was not reflected in its external behaviour. Attack and escape both decreased in frequency from January through March. Birds also tolerated each other at closer distances. Likewise the behaviour elements associated with attack and escape tendencies diminished in frequency. This reduced the observer's ability to predict from a bird's behaviour if it would attack or escape. The reduced agonistic behaviour with season may have been the result of increased social organization of the birds using the feeding station, habituation to the strange stimuli associated with the feeder, or to increased hunger. The agonistic behaviour elements had strong signal value. If a bird showed behaviour elements indicative of an escape tendency, the rival escaped less and stayed more. Likewise aggressive behaviour in one bird elicited increased escape and reduced attack in the second. Finally, appeasement behaviour in one bird resulted in less attack and less escape in the second bird. The probabilities of attack, escape, and staying following a particular combination of behaviour elements changed with season. Therefore behaviour elements are not perfect reflectors of the underlying motivation of a bird.