The role of vocal signals in coordinating cooperative anti-predator behaviour.
Between 2007 and 2011, built on my thesis research and expanded my work to include two more themes: (i) understanding the role of information in determining the specific decisions made by individuals in cooperative contexts and (ii) determining how individuals react to the behaviour of collaborators in ways which minimise the risk of exploitation. I conducted experiments investigating the payoffs of information exchange within the sentinel system of pied babblers (Turdoides bicolor), a cooperatively breeding passerine. With collaborators (Dr. Andy Radford, Dr. Mandy Ridley and Dr. Linda Hollen), we quantified the benefit gained by foraging birds in the presence of a sentinel, and demonstrated that this benefit was contingent on the vocal signal produced by sentinels (Hollen et al. 2008). We demonstrated that sentinels filter information about ambient predation risk and that their calls provide a continuous source of information which group mates use to adjust their own anti-predator behaviour, and we quantified the benefit of this to group mates (Bell et al. 2009). We demonstrated that individual contributions to sentinel behaviour are influenced by predation risk (Ridley et al. 2010). We also demonstrated that babblers adjust their reaction to signals based on the reliability of the signaller, becoming less trusting of less reliable sentinels, and we quantified the consequences of these adjustments (Radford et al. 2009, 2011). Specifically, in the presence of a sentinel, foraging birds reduce their personal vigilance and spend more time foraging. However, the strength of the effect is reduced (i) when sentinels sit on lower perches, where they are less effective at detecting predators (Radford et al. 2009); and (ii) when the sentinel is a kleptoparasitic fork-tailed drongo, who occasionally give false alarm calls in order to steal food (Ridley et al. 2007; Radford et al. 2011). These studies culminated in the first experimental demonstration of active negotiation over individual contributions to a cooperative behaviour in non-humans (Bell et al. 2010).
The implications are profound: conflict over individual contributions occurs wherever individuals collaborate, and understanding how it is resolved is one of the great challenges of evolutionary biology. I argue that information exchange between individuals is critical to maintaining the stability of cooperation in large groups, and that the roots of sophisticated bargaining lie in simple exchanges similar to those observed in pied babblers. These data and ideas form the starting point for the project proposed here.