Species recognition by five macaque monkeys

Sixteen monkeys of five macaque species (Macaca fuscata fuscata, M. mulatta, M. radiata, M. nemestrina, andM. arctoides) pressed a lever to see a variety of pictures (35 mm slides) of seven macaque species including their conspecifics. The subjects were allowed to see the same picture for the duration of the lever press and were able to see the same picture repeatedly by pressing the lever within 10 sec after the previous release of the lever. When 10 sec passed after releasing the lever, the next picture was set on the slide projector. All monkeys exceptM. arctoides and two infantM. fuscata fuscata pressed the lever to see their conspecifics for the longest duration. For all of the adult subjects, a multivariate analysis of variance (MANOVA) based on the mean duration of lever pressing responses (D) and the mean interval between the responses (I) revealed that the data for conspecific stimuli were distributed at significantly different locations from those for at least one of six close species on a two-dimensional space constructed with D and I. These results suggest that adult macaque monkeys visually discriminate their conspecifics from close species based on the still images of them.