Help thine enemy: the evolution of short ranging signals.

The proximity risk model offers one possible explanation of honest signalling of aggressive intent in biology. This model assumes that the probability of successful attack is a function of the distance between the contestants and that this distance can be correctly estimated. This later assumption may not hold in nature where contestants have to estimate this distance under noisy conditions. Here I investigate with the help of a game theoretical model whether short-range ranging signals can be evolutionarily stable under such conditions. These signals can help the opponent to estimate the correct distance, thus they can promote honest signalling of intentions. Here I show that ranging signals that help the estimation of distance between opponents can be evolutionarily stable. However, such help only benefits those individuals who are able and willing to attack. As a result, ranging signals in themselves are an honest cue of proximity and in turn they are honest cues of aggressive intent. I give an example: \"soft-song\" in birds, and I discuss the predictions of the model.