Visual preference for closely related species by Sulawesi macaques

Five species of Sulawesi macaques were exposed to pictures of macaques, including all seven species living in Sulawesi island, Indonesia. The subjects were either pets or monkeys kept at the zoo. The duration of visual fixation to the pictures was in general longer for pictures of the subject's own species than those of the others. Such visual preference was in general clearer in males than in females. This suggests that Sulawesi macaques discriminate closely related species visually and the sharpness of this discrimination might be related to the sex. This visual preference may be considered as one of the possible factors to suppress general intergradation among Sulawesi macaques. © 1995 Wiley-Liss, Inc.