Hidden colour aversions in domestic chicks triggered by pyrazine odours of insect warning displays

The warning signals of toxic insects often combine pyrazine odors with conspicuous colorations, such as red or yellow. An investigation of these warning signals in prey choice experiments with birds shows that pyrazine interacts with red and yellow to trigger strong aversions to these typical aposematic colors that are not shown in the absence of the odor. Pyrazine is not inherently aversive and does not produce aversion when combined with a less conspicuous color. These provide the first proof that the purpose of multicomponent signals lies in the psychological responses produced by the interaction of different sensory components.