Effects of novel colour and smell on the response of naive chicks towards food and water

Abstract

Many warningly coloured prey emit a conspicuous smell of pyrazines when attacked by a predator and it has been suggested that this odour cue constitutes part of the prey's aposematic anti-predator defences. The aim of the study was to test the hypothesis that pyrazine odours enhance the neophobic response of birds towards prey that is novel in appearance. Naive domestic chicks, Gallus gallus domesticus, were presented with food or water that was either familiar or novel (coloured with food dye) in appearance, in the presence or absence of five different odours. The odours in question were 2-methoxy-3-sec-butyl pyrazine, 2-methoxy-3-isobutyl pyrazine, almond oil, vanilla oil and thiazole. Presence of each of the pyrazines and of almond odour increased the latency with which chicks ate or drank, but only when the food or water was a novel colour. The effect was weaker with vanilla odour and absent with thiazole. When odours of 2-methoxy-3-sec-butyl pyrazine and thiazole were paired with a novel-coloured environment, eating and drinking were not inhibited. This suggests that odours naturally associated with chemical defence in insects or plants do enhance neophobia, but only when presented in conjunction with prey that has a novel appearance. However, confounding factors such as differences in odour intensity cannot at present be excluded. The implications of the results for theories concerning the evolution of warning coloration are discussed.