Many Eyes Together : Investigating the Perceptual, Cognitive, and Social Foundations of Collective Detection in Bird Flocks

Abstract

Social information use is considered one of the key benefits of group living. For instance, in the context of predation, group members can rely on each other’s vigilance to detect approaching threats in a process known as collective detection. Despite the intuitive appeal of this hypothesis and extensive research on the topic, significant gaps remain in our understanding. Vision is expected to play a critical role in anti-predator vigilance, especially for species with wide visual fields, but the challenge of tracking and quantifying visual input has made it difficult to study. Additionally, detection itself has been historically hard to measure, often approximated through observable behavioral responses that may not accurately reflect the true timing of detection. Moreover, little is known about how information is transmitted across group members, how individuals cognitively interpret the behavioral cues of others and how these interactions scale to produce collective outcomes. This complexity is further compounded by the difficulty of distinguishing between detections based on individual perception versus social information. To address these questions, this thesis adopts an interdisciplinary approach, moving beyond traditional behavioral ecology to integrate insights from sensory ecology, cognition, collective behavior, social learning, and technological innovation. Chapter 1 established the importance of visual ecology in vigilance by using advanced motion-capture technology to track fine-scale head movements. It revealed the relationship between visual input, vigilance and escape responses, and specifically that the pigeons’ first “foveation” (directing their high-acuity visual area) toward the predator cue could be used as a reliable proxy for detection in our system. Some evidence of social influence in escape responses was also observed. Chapter 2 explored gaze following, a widespread social cognitive trait, within a collective behavior context, to investigate how pigeons interpret subtle social cues in a group setting. This chapter demonstrated that pigeons follow the gaze of conspecifics, with the strength of their response increasing with the number of demonstrators. Chapter 3 integrated these findings using a Bayesian network-based diffusion model, adapted from social learning framework, to model information transmission during collective detection. It showed that pigeons used peripheral vision to monitor conspecifics' gaze orientation and detect predators, suggesting the role of gaze following to collectively detect predators. In addition to providing the first empirical evidence of gaze following as a functional mechanism in this context, these findings demonstrate that pigeons can interpret subtle social cues during collective vigilance. We propose that gaze following allows pigeons to acquire predator-related information early in the anti-predator response, enabling them to assess threats independently and make more informed decisions. These results underscore the role of perception in the context of vigilance to acquire environmental and social information, and more particularly for accurately measuring detection. They also reveal how social cues are cognitively processed during predator detection, and how social information is used at the collective scale. Overall, this thesis highlights the value of an interdisciplinary approach in addressing long-standing questions about collective vigilance and the benefits of group living, while encouraging future research to integrate new perspectives and methodologies from additional fields.