Does a novel bright colour patch increase or decrease predation? Red wings reduce predation risk in European blackbirds

Abstract

Bright coloration in animals may be explained by sexual selection, defence against predators (aposematism), and other factors. However, the initial evolution of colourful coats is unclear. Theoretical models often assume that rare, bright mutants suffer increased predation risk. In the blackbird Turdus merula , I tested whether a novel colourful plumage, resembling that of some American and African birds, increases or decreases the risk of predation. Pairs of stuffed blackbirds were exposed in the field, one with a bright red wing patch and one with normal wing colour. Predators (mostly goshawks) attacked normal mounts more often than mounts with red wings. Thus, in contrast with what is often assumed, a colourful mutant may be favoured by a decreased risk of predation. In addition, apostatic selection by predators may favour such mutants over longer time periods. These possibilities have important consequences for the evolution of bright coloration in profitable as well as unprofitable prey.