In Japan, the species is known as Nihonzaru (ニホンザル, a combination of Nihon 日本 "Japan" + saru 猿 "monkey") to distinguish it from other primates, but the Japanese macaque is very familiar in Japan — as it’s the only species of monkey in Japan — so when Japanese people simply say saru, they usually have the Japanese macaque in mind.
The Japanese macaque is sexually dimorphic. Males weigh on average 11.3 kg (25 lb), while females average 8.4 kg (19 lb). Macaques from colder areas tend to weigh more than ones from warmer areas. The average height for males is 57.0 cm (22.4 in), while the average female height is 52.3 cm (20.6 in). The size of their brain is approximately 95 g (3.4 oz). Japanese macaques have short stumps for tails that average 92.5 mm (3.64 in) in males and 79.1 mm (3.11 in) in females.[6] The macaque has a pinkish face and posterior. The rest of its body is covered in brown or greyish hair. The coat of the macaque is well-adapted to the cold and its thickness increases as temperatures decrease. The macaque can cope with temperatures as low as −20 °C (−4 °F).
Macaques mostly move on all fours. They are semiterrestrial, with females spending more time in the trees and males spending more time on the ground. Macaques are known to leap. They are very good swimmers and have been reported to swim a distance of more than half a kilometer. The lifespan of Japanese macaques is up to 32 years for females and up to 28 years for males, which is high when compared to what typically is seen in other macaque species.
Japanese macaques live in matrilineal societies, and females stay in their natal groups for life, while males move out before they are sexually mature. Macaque groups tend to contain several adults of both genders. In addition, a Japanese macaque troop contains several matrilines. These matrilines may exist in a dominance hierarchy with all members of a specific group ranking over members of a lower-ranking group. Temporary all-male groups also exist, composed of those who have recently left their natal groups and are about to transfer to another group. However, many males spend ample time away from any group, and may leave and join several groups.
Females of the troop exist in a stable dominance hierarchy and a female's rank depends on that of her mother. Younger females tend to rank higher than their older siblings. Higher-ranking matrilines have greater social cohesion. Strong relationships with dominant females can allow dominant males to retain their rank when they otherwise would not. Males within a group normally have a dominance hierarchy, with one male having alpha status. The dominance status of male macaques usually changes when a former alpha male leaves or dies. Other ways in which status of male hierarchy changes, is when an alpha male loses his rank or when a troop splits, leaving a new alpha male position open. The longer a male is in a troop, the higher his status is likely to be.
Females typically maintain both social relationships and hygiene through grooming. Grooming occurs regardless of climate or season. Females who are matrilineally related groom each other more often than unrelated individuals. Females will groom unrelated females to maintain group cohesion and social relationships between different kinships in a troop. Nevertheless, a female will only groom a limited number of other females, even if the group expands. Females will groom males, usually for hygienic purposes, but that behavior also may serve to attract dominant males to the group. Mothers pass their grooming techniques to their offspring, most probably through social rather than genetic means, as a cultural characteristic.
