The social context of a territorial dispute differentially influences the way individuals in breeding pairs coordinate their aggressive tactics

Abstract

In diverse species, individuals coordinate behavior to accomplish shared goals or tasks. Such coordination, however, often occurs selectively, and the contextual information animals use to determine when they coordinate and when they do not is unclear. We investigate this issue in the highly territorial downy woodpecker (Picoides pubescens) by exploring how individuals within a social breeding pair differentially modulate coordinated aggressive responses during graded simulated territorial intrusions (STIs). Analyses show that resident pairs mount a more robust aggressive response to STIs that represent a greater threat. Moreover, in this social context, pair members produce contact vocalizations in a way that predicts their partner’s aggressive behavior. We also show that, when presented with a low threat, individuals that first respond to intrusions decrease their aggressive output once their partner attends to the stimulus; the partner, in turn, increases their levels of aggressive behavior. This does not occur in high-threat STIs, where both partners maintain high levels of aggression throughout the entire encounter. Together, these results show that individuals within a pair flexibly adjust their aggressive tactics in response to different social competitive contexts, and this includes adjusting the way in which individuals coordinate certain aspects of their agonistic repertoire. We speculate that this ability reflects an adaptive mechanism that allows individuals to fine-tune territorial tactics to reduce overall costs of aggression. Although research has demonstrated that individuals often coordinate their behavior to accomplish common tasks, little is known about the factors that determine when such coordination occurs and when it does not. We address this issue for the first time in the highly territorial downy woodpecker by testing how the level of threat associated with a territorial interaction influences the coordination of defensive behavior. We find that, when facing intruders that pose a greater threat, residents adjust levels of aggressive output in response to the number of vocalizations produced by their breeding partner. By contrast, this relationship is not observed when pairs face intruders that pose a relatively lower threat. Our data therefore provide striking evidence that coordination in defensive tactics depends on the residents’ appraisal of the social context, such that fiercer competition is associated with greater behavioral coordination.