The evolution of cooperation in avian mobbing

The existence of cooperative groups evokes the interlinked problems of how individuals ultimately benefit from being in a group and how they coordinate their behavior to join groups. Theoretical models are often framed in terms of a cooperating pair, but an increasing number of studies allow for cooperative groups to contain more than two individuals. For larger groups, there are challenges both in ensuring payoffs when interacting with many others and coordinating the behavior of participants, particularly when individuals rely on recognizing others and being recognized themselves to benefit from a cooperative behavior. Few models have accounted for the role of these proximate mechanisms in the formation of large cooperative groups and most have, instead, simply assumed that all potential participants decide whether or not to join. In natural systems, however, proximate mechanisms may critically affect the nature of cooperation in terms of how individuals evaluate the payoffs of joining a group and the resultant sizes of groups that are formed. I developed a model of cooperative groups that takes into account the proximate mechanisms facilitating their formation, the predictions and assumptions of which I empirically tested in a natural system of avian mobbing behavior. The results demonstrate that, under the right conditions, cooperative groups can form readily even when individuals are risk-averse, and that understanding how groups form is fundamental to understanding why they form.