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A complex plumage pattern as an honest social signal

Although there are numerous studies of the social significance of bird coloration, the vast majority of these deal with either variation in hue, or the amount of area of the body that is pigmented. Although it is common for birds to show intricate patterns by combining feathers of different colours, this has rarely been studied. We describe and analyse a bold pattern of black bands that cover the sides of the body of the red-legged partridge. By combining feathers of a specific length in a particular anatomical location, these bands align vertically during a display. The amount of black in each feather is correlated with body condition, and so may be used by other individuals (e.g. opponents during a territorial contest) to assess the quality of the bird. As social signals, patterns have the advantage of being able to be turned off and on when appropriate by behavioural modification.