Collective signaling in a communally breeding bird, the greater ani

Abstract

Animals living in more complex social environments typically display greater communicative complexity than those living as solitary or pair-living individuals, as the selective pressures associated with group-living drive more diverse and sophisticated modes of communication, and as more flexible, varied signals facilitate the evolution of more complex societies. Within and across social groups, the communication networks in which group-living animals are embedded feature multiple potential signalers and receivers who interact in close spatiotemporal proximity. The collective and simultaneous signaling and receiving that occur within these communication networks can be adaptive or maladaptive, depending on the individual and the context, and, together, are an excellent example of some of the unique behavioral and communicative challenges associated with living in a cooperative group. In my dissertation, I explore multiple aspects of collective signaling behavior in a communally breeding Neotropical cuckoo, the greater ani (Crotophaga major). Greater anis form breeding groups composed of two or three unrelated pairs and lay eggs in a single shared nest, cooperatively raising each other’s young. Working with a wild study population in central Panama, I used field observations, video recordings, and acoustic analyses to explore collective signaling within the context of the greater ani communal breeding system. In Chapter One, I first consider signaling interactions between dependent young and their adult caregivers, testing whether reliable begging signals can persist when average relatedness between nestling signalers and adult receivers is low. Building on these results, I then examine in Chapter Two whether adult prey delivery rates and nestling competition over resource consumption change as a function of the number of caregivers in a group and/or the number of dependent young. In Chapter Three, I evaluate whether an intriguing collective vocalization, the group chorus, is primarily used for intra- or extra-group communication, as anis navigate their broader social landscape. Each chapter contributes to our understanding of how social animals respond to the unique challenges and opportunities associated with group living, and how communication can play a critical role in these social interactions.