Collective responses to antipredator recruitment calls in the jackdaw (Corvus monedula)
Coomes, Jennifer Rose
Thesis or dissertation
University of Exeter
Reason for embargo
I wish to publish a paper from a chapter of my thesis.
Collective behaviour, whereby multiple individuals act together in a coherent, coordinated manner, occurs throughout nature. Self-organisation theory suggests that the maintenance of the collective behaviours shown by bird flocks and fish shoals, emerge as the result of simple rules of attraction among neighbours, with no need for leadership. Individuals in the models of self-organisation are assumed to be identical but in reality animals differ in aspects such as personality or motivation and in their social bonds with other conspecifics. Individual variation among group members means that certain individuals may exert disproportionate effects on the behaviour of groups and so in some cases, leadership is important for the initiation of collective behaviours. Moreover, cognitive processing of information about other individuals may play an important, but hitherto neglected role in the coordination of collective behaviours. This thesis examines the role of cognitive processes and of leadership in the formation of collective antipredator mobbing events in wild jackdaws (Corvus monedula). Mobbing presents a collective action problem as it entails substantial risks for individuals but, by driving away potential predators, provides collective benefits. Individuals may therefore benefit from processing information about the likely costs and benefits when deciding whether to join a mob. Recruitment to a mob is initiated through distinctive scolding calls, and information contained in these calls may be very valuable for individuals when deciding whether to join mobbing events. Chapter Two tested whether the number of callers influenced the number of individuals recruited to a mob. Individuals are expected to join a larger group because for an individual there is a reduced risk of predation. As predicted, I found that a greater number of callers does recruit a greater number of individuals. This work shows evidence that jackdaws discriminate between the calls of different individuals and is the first to show numerical assessment in an antipredator collective behaviour. Chapter Three tested whether the dominance rank of caller influenced the number of individuals recruited to a mob. A dominant individual may be expected to recruit more individuals as it is likely to be stronger and more able to drive away a predator. A dominant may also punish others for not responding. However, I found no influence of dominance rank of caller on the number of recruits. Punishment is unlikely to be important in jackdaw societies and any effect of rank may be obscured by other factors such as direct benefits from joining the mob, not contingent on dominance rank. Social relationships between the recruits and the caller have not been considered in this study and individuals may be more likely to respond to a close affiliate than pay attention to an individual’s dominance rank. Together, these results highlight the importance of investigating the cognitive processes involved in collective behaviours and also the characteristics of individuals who initiate collective behaviours.
MbyRes thesis on collective responses to antipredator recruitment call in the jackdaw with particular focus on numerical assessment and the influence of dominance rank.
MbyRes in Biological Sciences