Receiver bias for colourful signals

Animals tend to respond more strongly to signals that are more colourful and such signals are also common in nature. This is the first study to explore experimentally the possibility that response biases arising in an animal's recognition mechanisms can explain these findings. We trained domestic fowls, Gallus gallus domesticus, to respond by pecking or not pecking to different colours displayed on a touch-sensitive computer screen. The colours changed in response to the birds' choices, which mimicked a simple evolutionary process. Discrimination training generated response biases for the colours more distinct from the nonrewarding colour. As a result the signals evolved towards distinct coloration. The biases developed in directions towards more intense and towards less intense colour, depending on the colour of the nonrewarding stimulus. The result may be applicable to all sorts of visual signals encountered during the same kind of experiences, that is, when one signal should be avoided and another should be approached. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.