Colour biases are a question of conspecifics’ taste

Toxic prey often advertise their defences to predators using conspicuous colours, such as red and yellow; and predators exhibit unlearned biases against warningly coloured food. These biases are particularly evident when other components of warning displays, such as sounds and odours, are present. Predators are thought to use additional signal components to reduce their attack rates on warningly coloured prey when the risk of them being defended is perceived to be high. If this is the case, any cue that allows predators to predict the presence of defended prey reliably should incite biases against warningly coloured food. Using domestic chicks, Gallus gallus domesticus, as predators and coloured crumbs for prey, I tested whether observing a conspecific’s distaste response caused predators to bias their foraging decisions away from warningly coloured prey. Chicks observed a conspecific that had been given either a drop of water or a drop of Bitrex (a bitter-tasting solution). They were then offered a choice of either red and green, or yellow and green crumbs. Chicks that observed a conspecific’s reaction to Bitrex attacked fewer red and yellow crumbs, and more green crumbs, than chicks that observed a conspecific’s reaction to water. Observing conspecifics’ disgust responses therefore caused birds to bias their foraging preference away from warningly coloured food and towards food of a more neutral colour. This suggests that predators’ social systems may play a more important role than previously thought in the evolution of prey defences.