Novelty effects in a multimodal warning signal

The warning signals of toxic insects are often 'multimodal', Combining brig ht coloration with sounds or odours (or both). Pyrazine (a common insect wa rning odour) can elicit an intrinsic avoidance in domestic chicks, Gallus g allus domesticus, both against novel coloured food, and also against food c olours that are specifically associated with aposematism, namely yellow and red. In three experiments, we investigated the role of novelty in this inn ate bias against yellow coloured food in the presence of pyrazine. Naive ch icks were familiarized either to pyrazine odour or to coloured food before being tested for a bias against yellow (warningly coloured) food as opposed to green (nonwarningly coloured) food. In experiment 1, pyrazine novelty w as shown to be vital for eliciting a bias against yellow food. However, exp eriment 2 suggested that colour novelty was not important: chicks familiari zed with coloured crumbs still avoided yellow crumbs when pyrazine was pres ented. In a third experiment that gave chicks an even greater degree of pre -exposure to coloured crumbs, the bias against yellow food eventually waned , although pyrazine continued to elicit an aversion to yellow even after bi rds had had experience of up to 24 palatable yellow crumbs. Pyrazine novelt y has been an important pressure in the evolution of multimodal warning sig nals, and can continue to promote the avoidance of warningly coloured food, even when it is relatively familiar. The implications for warning signals are discussed. (C) 1999 The Association for the Study of Animal Behaviour.