Scientists have found how "immigrant" monkeys make friends with other species to be accepted in their new community.
Diana monkeys tolerate immigrating putty-nosed monkeys
Research by psychologists at St Andrews University found that the monkeys co-existed successfully and helped defend their neighbours against predators.
This was despite competing for the same living space and food.
The work was conducted by Dr Klaus Zuberbuhler of St Andrews over a period of two years in an area of rainforest in West Africa's Ivory Coast.
Co-operation and co-existence
Dr Zuberbuhler said: "Our results show that Diana monkeys tolerate immigrating putty-nosed monkeys and form mixed-species groups with them because of their merit in predation defence.
"Particularly, male putty-nosed monkeys play a vital role in defence against crowned eagles, suggesting that putty-nosed monkeys obtain access to feeding trees by offering anti-predation benefits to Diana monkeys."
The scientists tested for levels of co-operation and co-existence between forest monkeys.
Because of the merits of warning fellow primates of would-be predators, the immigrant species was welcomed to the existing community.
Putty-nosed monkeys offer anti-predation benefits to Diana monkeys
Seven species of monkeys managed to co-exist peacefully in the same community, although this meant they had to restrict their living space to separate areas of the forest so they would not be competing for food.
Dr Zuberbuhler said: "Diana monkeys typically forage in the highest tree crowns, while the closely related Campbell's monkeys exploit the vegetation close to the ground.
"Such niche separation decreases interspecies competition and makes co-existence of closely related species possible."
The findings of the study are published in the paper "Co-operation and competition in two forest monkeys" in the current issue of Behavioural Ecology.