Japanese Macaque

About the Japanese macaque

The Japanese macaque, commonly known as the snow monkey, is a terrestrial Old World monkey native to Japan and the northernmost-living non-human primate on Earth — no other primate lives farther north or in a colder climate. In Japan it's called Nihonzaru, but since it's the country's only native monkey species, Japanese speakers often just say saru, "monkey," and mean this animal by default. It has brownish-grey fur, a pinkish-red face, and a short, stubby tail averaging 92.5 mm in males and 79.1 mm in females.

The species is sexually dimorphic: males average 11.3 kg and stand 57.0 cm tall, while females average 8.4 kg and 52.3 cm, with individuals from colder regions tending to weigh more than those from warmer parts of the range. Its brain weighs approximately 95 grams. The macaque's coat thickens as temperatures drop, letting it tolerate conditions as cold as −20°C (−4°F). It moves mainly on all fours and is semiterrestrial — females spend more time in trees, males more time on the ground — and it is a capable swimmer, with individuals recorded crossing more than half a kilometer of open water. Lifespan runs unusually long for a macaque species: up to 32 years for females and 28 for males.

Two subspecies are recognized, including M. fuscata yakui, found on the southern island of Yakushima. The species occupies the three main Japanese islands of Honshu, Shikoku, and Kyushu, south of a biogeographic boundary called Blakiston's Line, along with several smaller islands; the northernmost population lives on Honshu's Shimokita Peninsula. A 1989 survey estimated the total wild population at 114,431 individuals.

Behavior and diet

Japanese macaques live in matrilineal societies. Females remain in their birth troop for life and inherit their social rank from their mothers, with younger females typically outranking older siblings; males leave before reaching sexual maturity and may drift between troops or spend long stretches outside any group entirely. Within a troop, males maintain their own separate dominance hierarchy topped by a single alpha, a position that changes hands when the previous alpha leaves, dies, or is displaced, or when a troop splits. One especially striking case comes from Takasakiyama Natural Zoological Garden, where a female named Yakei overthrew the troop's dominant males — and her own high-ranking mother — to become, at age nine in 2021, the first female leader in the 677-monkey troop's 70-year recorded history.

Grooming is central to macaque social life, done year-round regardless of season, mostly between related females, though females also groom unrelated females to build alliances and groom males largely for hygiene. During the mating season, a male and female form a temporary pair bond, traveling, feeding, and resting together for an average of 16 days; females typically consort with about four males a season, and higher-ranking males tend to hold longer consortships and try to disrupt those of subordinates, although females themselves decide when and with whom mating occurs. Mothers give birth on the ground, usually at the edge of the troop, and carry infants on their bellies for the first four weeks before switching to their backs; infants begin eating solid food at five to six weeks, forage independently by seven weeks, and are fully weaned by eighteen months.

The species is also known for cultural, learned behavior. On Koshima Island, researchers watched a female named Imo begin washing sweet potatoes in river water rather than brushing off the sand, then dipping the food in seawater to season it — behavior that spread through her troop and was passed down to later generations. Japanese macaques are also known to bathe together in hot springs in winter, a practice associated with lower stress levels, and to roll snowballs, along with developing regional differences in the pitch of their calls, comparable to accents.

Range and habitat

The Japanese macaque is found on Honshu, Shikoku, and Kyushu, plus a number of smaller Japanese islands, occupying habitats from subtropical forest in the south of its range to subarctic mountain forest in the north. It uses both warm, broadleaf evergreen forest in the southwest and cool, deciduous forest across central and northern Japan, with warm and cool temperate forest types serving as its most important habitats overall.

Outside Japan, the species has one notable established population: in 1972, roughly 150 macaques were relocated from Kyoto to a primate observatory in southwest Texas, where they were largely left to roam an enclosed, ranch-style arid brushland habitat. Many died adjusting to the unfamiliar environment at first, but the survivors adapted, learning to avoid predators such as eagles, coyotes, and rattlesnakes and to forage on mesquite beans and cactus fruit; by 1995 the troop had grown to 500–600 individuals. Following an incident in 1996 in which hunters killed or maimed four escaped macaques, a 186-acre sanctuary was established near Dilley, Texas, which by 2017 also housed six other macaque species.

Conservation status

The Japanese macaque is listed as Least Concern by the IUCN. Historically, threats to the species came from slash-and-burn agriculture, logging for construction and fuel, and hunting, but these pressures have declined since World War II amid Japan's broader social and economic changes, including a 1947 law prohibiting macaque hunting.