Behavioral responses of free-ranging Japanese macaques (Macaca fuscata) to sudden loud noises

We opportunistically observed 31 cases of responses to sudden loud noises mainly caused by falling rocks and trees in a free-ranging, provisioned group of Japanese macaques, Macaca fuscata, at Katsuyama, Japan, and analyzed 27 cases for which we successfully recorded their responses. In 88% of the 24 cases in which the highest- or second-highest ranking adult male probably heard the noise, one or both of them vocalized aggressively in response. Other males tended to vocalize when they were far away from the two highest-ranking males (in 5 of 7 cases in which they vocalized). Adult females vocalized in only 8% of cases, even when they fled from the noise source. These findings suggest that, unlike tree-shaking and female-directed aggression - both performed often in the mating season and accompanied by vocalizations in both high- and low-ranking males of Japanese macaques - vocalizing in response to sudden loud noises is usually limited to one or two high-ranking males in the vicinity. This vocal response could be a way for the males to advertise their social status; it may also serve to calm group members scared by the noise, preventing them from fleeing in panic and dispersing widely. Our observations also suggest that males may monitor which other males remain nearby, and that whereas females may scream in response to socially induced fear, they are least likely to do so in response to fear arising from non-social contexts.