Differential responses of yellow-breasted chats, Icteria virens, to male and female conspecific model presentations

A detailed understanding of the behavioural interactions between males and females is crucial for elucidating the selection pressures shaping mating system evolution; however, these interactions are often difficult to observe, particularly in free-living populations. We simulated extraterritorial intrusions by presenting conspecific models on to territories of a Neotropical migratory passerine, the yellow-breasted chat, Icteria virens. Simulated intrusions elicited different responses based on the sex of the focal individual and the sex and species of the model. Behavioural responses of the focal individuals were largely directed towards conspecific models, whereas simulated heterospecific intrusions, using a Carolina wren, Thryothorus ludovicianus, model, elicited minimal response. Male song was not related to any particular model presentation. Males directed mating behaviours, including courtship displays and copulations, exclusively towards the female conspecific model. Males behaved aggressively towards the conspecific male model. In contrast, females never showed any courtship behaviour towards the male model and showed significant aggression towards the conspecific female model. The results of this study reveal that territorial aggression in yellow-breasted chats is strongly intrasexual. Additionally, simulated female extraterritorial intrusions, but not male intrusions, resulted in extrapair courtship and copulation. This pattern is likely to be typical of many socially monogamous species and points to the behavioural mechanisms underlying both monogamy and extrapair mating systems.