Blue Tit (Parus Caeruleus) Agonistic Displays: A Reappraisal

Abstract

Abstract1. In order to reappraise work by Stokes (1962a, b) and subsequent interpretations of his results, a data set involving 906 dyadic Blue Tit interactions was coIlected and analysed using video playback. 2. A number of shortcomings in Stokes' original approach were highlighted, including his broad definition of attack and a lack of information on the true frequency of behaviours and of combinations of elements at an instance in time. 3. A total of 16 behaviours and actions with a clear agonistic context were identified. Similarity indices (Jaccard Index) were calculated based on the co-occurrence of behaviours at an instance in time. No behaviours were associated at a high enough level to warrant their consideration solely as compound displays. 4. True attack was rare, unpredictable and effective. Escalated fights occurred in < 1% of interactions, with peck attacks which were not escalated into fighting in a further 2% of interactions. The rarity of true attack makes it more useful to look at the relationship between behaviour and interaction outcome (win/lose), than between behaviour and subsequent actions (attack/stay/escape). 5. Seven behaviours were associated with winning (e.g. Wings out, Nape erect) and three (e.g. Crest erect) with losing. However, no behaviour was restricted to only one of these roles, no behaviour precisely predicted winning or losing, and many birds won or lost without showing these behaviours. Crest erect is associated with fear but is not simply a surrender signal. 6. In addition to the displays investigated, several other factors are thought to be involved in contest resolution. These are briefly discussed.