Aggressive communication in fulmars (Fulmarus glacialis) competing for food

A simple model which considers communication of subjective resource value during aggressive encounters is developed. If different behavioural patterns differ in effectiveness (probability of winning) the model predicts that: (1) the expected cost should differ for different behaviour patterns; (2) when effectiveness increases, the associated cost should increase; and (3) the optimal choice should be influenced by the value the resource represents for the animal. These predictions were tested on field data from 1383 interactions between fulmars competing for food. In these interactions, one bird was the ‘owner’ who defended the food item and during the time of ownership ate pieces of the food item. The owner was regularly challenged and take-overs occurred in 22% of interactions. The effectiveness of a given behaviour pattern was measured as the proportion of interactions won. The cost was measured as the proportion of interactions that entailed physical fighting. Resource value was estimated indirectly by comparing time as owner with choice of behaviour. The results indicate that an animal's choice of behaviour influenced its probability of victory, and expected cost, and that effectiveness and cost correlate positively. Furthermore, the frequency with which different behaviours were observed is influenced by the value of the resource for the bird.