Collective anti-predatory behaviour in animals groups

Abstract

The collective behaviour of animal groups serves to reduce the risk of predation to individuals. By joining a group individuals remain in close proximity to others which reduces the risk of predation. Groups can also afford benefits by allowing for early detection of predators. During predatory attacks groups may confuse or deter predators by making it difficult for single individuals to be targeted. The mechanisms underlying many aspects of collective behaviour in response to predation are not well known. Here we review the models and studies of collective responses to predation and propose some underlying mechanisms for collective detection, evasion and communication about predators. In foraging flocks collective detection benefits individuals by providing them earlier detection of predators then when alone. Vigilance behaviour of neighboring individuals is copied. The amount of individuals displaying vigilant behaviour reaches a threshold level where the group initiates escape behaviors. Therefore predators raise vigilance levels and allow individuals to detect and escape predation earlier. Predators also attack free flying or free swimming groups. Here information about the location fo the predator may be spread through agitation wave. These waves of changing density have been shown the orient individual group members towards the location of the predator. These waves may also serve to confuse a predation attempt by making it harder for a predator to single out an individual within the group. Often prey species possess highly reflective feather or scale which reflect waves of light during agitation wave propagation, which may in turn further the confusion effect. In addition to performing waves free flying / swimming groups also exhibit consistent flocking patterns. These patterns have been shown reflect the level of predation risk experienced at certain areas. It is possible that flocking patterns represent honest signals of environmental conditions and may therefore serve as communication becons to other groups. Findings that neighboring groups tend to copy flocking patterns lends some support for this, albeit its mechanisms are unknown. However all aspects of collective behaviour involve groups moving and making decisions as a coordinated whole. Collective anti-predatory behaviour could be caused through individual threshold responses leading feeding back to collective group level behavior. In all situations individual responses to the presence or attack of a predator reaches a certain level when positive feedback , through coping neighboring behaviors, spreads this behaviour through the entire group. This process allows groups to make informed and accurate decision when detecting, evading and communicating about predators.