Discrimination of macaques by macaques: the case of Sulawesi species

A series of work by the first author have demonstrated that many macaque species show a visual preference for the pictures of their own species when the monkeys actively press a lever to see the pictures. We expanded this study to Sulawesi macaques kept as a pet by local people with slight modification. All seven species of Sulawesi macaques were passively exposed to a variety of colored slides of Sulawesi macaques. The experimenter recorded the duration of visual fixation onto the pictures. Male monkeys of all the seven species clearly watched the pictures of their own species for longer duration than those of the other species. Such visual preference suggested that the seven Sulawesi macaques discriminate each other species and, thus, they may not be integrated into fewer number of species. This visual preference may work to prevent overall intergradation of the Sulawesi macaques who sometimes have hybrid zones only in limited areas. This preference was in general weaker in female monkeys. In one species,Macaca ochreata, females actively avoided to see the pictures of conspecifics. These results may be related to how female monkeys interact with other individuals.