[Populational differences of vocal behavior in Japanese monkeys]

This study suggested the possibility of vocal learning in the Japanese monkey (Macaca fuscata) by examining populational differences in the calls of individuals from two populations, the Ohirayama and Yakushima. Genetic variability of these two populations is very small. Japanese monkeys emit a class of contact calls known as the "coo" call. The coo calls of 41 subjects (30 animals from the Ohirayama group and 11 animals from the Yakushima group) were analyzed spectrographically. There are significant differences between the two groups in four parameters of coo calls (minimum frequency, start frequency, duration to the maximum frequency, and total duration). Individuals in the Ohirayama group emit coo calls lower in frequency and longer in duration than those in the Yakushima group. The results suggest the possibility that the populational differences of coo calls are due to learning.