Female Contests for Nest Sites and Mates in the Pied Flycatcher Ficedula hypoleuca

Abstract

Predictions of game theory models about the outcome of animal conflicts have most often been tested using male contests for mates, territories or food. We studied female contests for nest sites and mates in the pied flycatcher, Ficedula hypoleuca, and asked which factors affect the outcome and duration of the contests. Conflicts over residency were experimentally induced, but natural cases in which both females regarded themselves as owners were also included in the analyses. The ensuing escalated contests involved physical fighting, defence of the nestbox of the male and alarm calling. Contrary to expectations from game theory, fighting seemed to occur most often at the start of conflicts, whereas alarm calling occurred towards the end and nestbox visits throughout the conflict. The outcome of the contests was not determined by asymmetries in body size or age, nor by a simple previous-present owner asymmetry. Instead, it depended on the relative residence times of the opponents. The duration of the contests tended to increase with decreasing asymmetry in the residence times of females, whereas body size asymmetries had no influence. Because there is intense competition between females for a mate in the pied flycatcher, we suggest that females do not respect asymmetries in residency and body size, but fight in relation to the value of the mating opportunity. In particular, we point to the possibility that the value of a mating opportunity may increase with residence time because knowledge of other mating options may become outdated.