Pyrazine odour makes visually conspicuous prey aversive

Unpalatable insects frequently adopt multimodal signals to ward off predato rs, incorporating sounds and odours into their colourful displays. Pyrazine is an odour commonly used in insect warning displays, and has previously b een shown to elicit unlearned biases against common warning colours, e.g. y ellow and red in naive predators. We designed two experiments to test for s imilar effects of pyrazine on the conspicuousness of prey, perhaps the most ubiquitous aspect of aposematic coloration. In the first experiment, we of fered predators (Gallus gallus domesticus) a choice between conspicuous cru mbs and cryptic crumbs in the presence or absence of pyrazine. In the secon d experiment, we manipulated the birds' experience of conspicuous prey duri ng an initial training phase. Only in the presence of pyrazine did birds sh ow a bias against conspicuously coloured food, and this occurred whether or not they had previously experienced food that contrasted with the backgrou nd This emergent behaviour relied upon the visual and odorous signal compon ents being presented together. These unlearned, yet hidden, responses again st conspicuousness demonstrate that there are initial benefits to prey bein g conspicuous when the multimodal nature of warning signals is accounted fo r.