Is red an innate or learned signal of aggression and intimidation?

Red coloration has been associated with dominance and aggression in a number of animals. However, it is unclear whether the increased aggression of red individuals or the avoidance of red opponents is an intrinsic or learnt response. By experimentally controlling for genetic and environmental effects, I tested for innate competitive differences and red-enhanced contest success in sexually immature (uncoloured) red and black head colour morphs of the Gouldian finch, Erythrura gouldiae. Despite juveniles being reared by foster parents of the same and different colour morphs, there were no differences in competitive abilities between uncoloured red and black males. However, when I experimentally added a red head mask to uncoloured males, red (but not black and novel blue coloration) was associated with winning contests, irrespective of an individual's underlying genetics or postindependence social experience. In addition, uncoloured opponents expressed higher stress responses (corticosterone) and avoided conflicts with red-painted competitors. The association between red coloration and aggression may be an innate response to aid facultative fight or submissive decisions, and adds to growing evidence suggesting that red coloration may be a general signal of intimidation.