Artificial colour treatment mediates aggression among unfamiliar vervet monkeys (Cercopithecus aethiops): a model for introducing primates with colourful sexual skin
Aggression and agonism typically accompany the initial interactions exchanged between unfamiliar primates. As a part of a larger study examining the social function of scrotal colour in vervet monkeys (Cercopithecus aethiops sabaeus), this paper offers experimental data to show
how scrotal colour can influence aggression, and how artificial colour treatment can be used as an effective tool for managing aggression. Study animals were 81 vervet monkey pairs composed of 162 similarly-sized, unfamiliar adult males originating from non-adjacent parishes in Barbados. Non-contact
and contact aggression were recorded on a continuous basis during 90 minute introductions. The main effects of the Test male scrotal colour, Stimulus male colour, and the interaction of the Test male and Stimulus male colours were not significant predictors of non-contact aggression. The effects
of scrotal colouration of the Test male and Stimulus male were not significant predictors of contact aggression either, but there was a significant interaction effect; pairs of males with similar scrotal colour engaged in contact aggression more often than pairs of males differing in colour.
Painting the scrotum dark led to more aggression when these males were paired with dark coloured males and less aggression when these males were paired with pale coloured males. These findings suggest a practical and inexpensive means of reducing the likelihood of aggression when introducing
new animals. These results may also be applicable for other taxa that have colourful sexual skin, such as mandrills, drills, talapoins, patas monkeys, and many guenon species.