Primate visual signals in noisy environments

Most animals and plants need to send signals and rely on some sort of response. For an active receptor of signals, virtually all the signal transmissions that litter the environment, bar those that are functional at any given moment, can be described as 'noise'. I concentrate here on some primate examples where loud calls combine with 'loud' colouring and patterns, to suggest that increasing the intensity of signals can help overcome the problem of 'noise'. I also present evidence that certain ecological conditions favour use of the visual channel. I use some examples, drawn from African guenons, to suggest that visual patterns broadcast on this channel have evolved and have, effectively, been elaborated to conform with certain optical principles. These optical properties minimize ambiguity and enhance species-specific (or at least population-specific) distinctiveness. The abilities of ancestral forest primates to discriminate between functional signals and visual 'noise' may have played an important part in providing the basis for our own hominin ancestors' visual proficiencies.