The Japanese macaque (Macaca fuscata) is a terrestrial Old World monkey species. Colloquially, they are referred to as "snow monkeys" because some live in areas where snow covers the ground for months each year - no other non-human primate is more northern-living, nor lives in a colder climate. In Japan, these monkeys are known as Nihonzaru (Nihon "Japan" + saru "monkey") to distinguish them from other primates, but Japanese macaques are very familiar in Japan, so when Japanese people simply say saru, they usually have in mind the Japanese macaque.
Japanese macaques have a pinkish face and posterior. The rest of their body is covered in brown or greyish hair. Their coat 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 and are known to leap.
Japanese macaques are found on three of the four main Japanese islands: Honshu, Shikoku, and Kyushu. They inhabit subtropical forests in the southern part of their range and subarctic forests in mountainous areas in the northern part of their range. They can be found in both warm and cool forests, such as the deciduous forests of central and northern Japan and the broadleaf evergreen forests in the southwest of the islands.
Japanese macaques live in groups of 20-30, led by the dominant male. Females stay in their birth group for life, but males leave the group before sexual maturity. Females spend more of their time in trees, while males spend most of their time on the ground. The dominant male has a role in siring young, deciding where the troop should go, and protecting the troop from predators and other macaque troops. Japanese macaques feel at home both in trees and on the ground. Females spend more time in the trees and males spend more time on the ground. They are very good swimmers, being able to swim over half a kilometer, and are known to leap. During feeding or moving, Japanese macaques often emit "coos". These most likely serve to keep the troop together and strengthen social relations between females. Coos are also uttered before grooming along with "girney" calls. Japanese macaques also have alarm calls for alerting to danger, and threat calls heard during aggressive encounters.
Japanese macaques are omnivores. Their diet includes smaller animals and plants, mainly fruits, berries, seeds, flowers, and young leaves. They also eat insects, crabs, and bird eggs during the winter months.
Japanese macaques are polygynadrous (promiscuous) meaning that both the males and females have multiple partners during each breeding season, which lasts 4 to 5 months between September and April. Females usually choose a mate by his rank. Births occur between March and September, after a gestation period lasting 6 months. Females usually give birth on the ground and infants are born with dark-brown hair. They consume their first solid food at 5 to 6 weeks old and can forage independently from their mothers by 7 weeks. Females carry their infants on their bellies for their first 4 weeks. After this time, they carry infants on their backs, as well. Infants continue to be carried past a year. Full weaning usually occurs when infants are 18 months old.
Japanese macaques face no major threats at the species level. However, around 10,000 macaques are killed by farmers every year, protecting their crops and livestock.
According to IUCN Red List, the Japanese macaque is locally common and widespread throughout its range but no overall population estimate is available. Currently, this species is classified as Least Concern (LC) on the IUCN Red List and its numbers today are stable. A study in 1989 estimated the total population of wild Japanese macaques to be 114,431 individuals.
Japanese macaques consume a variety of insects and plants and act as seed dispersers. They compete for some plants with Sika deer on Kinkazan Island, but when they climb trees to get the most energy-sufficient leaves, in the process they knock down leaves, which the Sika deer eat. Japanese macaque serves as an important prey species for mountain hawk-eagles, Japanese wolves, and raccoon dogs.