Japanese macaque

Name and taxonomy

In Japanese the animal is Nihonzaru, Japan monkey, but most people just say saru, monkey, because it is the only one they know. Edward Blyth described the species in 1875, and the type locality is simply Japan. An older name, speciosus of 1825, was suppressed by the zoological commission in 1970. The Yakushima macaque, Macaca fuscata yakui, was named by Kuroda in 1941. It has blackish fur on the backs of the hands, darker than its body, and lives only on Yakushima, about 60 km south of Kyushu.

The species belongs to the family Cercopithecidae, the Old World monkeys. Within the genus Macaca it falls in the fascicularis group, beside the rhesus macaque, the crab-eating macaque and the Formosan rock macaque. It is listed on CITES Appendix II and as Threatened under the United States Endangered Species Act.

Evolution and relatives

The macaque's ancestor was probably a monkey much like the rhesus macaque, living on the Korean peninsula. It crossed to Kyushu and western Honshu over land bridges that appeared when sea levels fell in the Middle Pleistocene. Those crossings happened during one or two glacial low stands of the sea. The oldest macaque fossils in Japan are a molar and an upper arm bone that look like the living species. Fossil macaques from Korea date from the same era, yet no monkey lives in Korea today.

Two subspecies are recognised: the mainland form and the Yakushima form. Like other macaques, the species probably spread north as forests shifted with the climate, and cold now sets its limit. The species has evolved a thick coat that grows denser as the temperature falls, and it copes with minus 20 degrees Celsius.

Appearance

The coat is long on the back and ranges from pale yellow-brown through grey-brown to dark golden brown. The belly and inner limbs are whitish to pale grey or buff. Pale side whiskers frame the face, and the hair often forms a small crest near the angle of the jaw. The face and rump are bare and pink to red, and both flush deeper in the mating season. The tail is very short and furry, and it may carry a white tuft at the tip. Northern monkeys tend to be paler and heavier than southern ones, and the whole coat is moulted in late spring.

Males average 11.3 kg and 57 cm, and females 8.4 kg and 52.3 cm. A male's body is about 9 percent longer and about 32 percent heavier than a female's. The tail averages about 9.25 cm in a male and 7.91 cm in a female. The brain weighs about 95 grams. Newborns are dark brown to blackish, much darker than adults, and take their adult colour by 4 to 5 months. Monkeys fed by people grow larger skulls than wild ones.

Habitat and range

The macaque lives on three of Japan's four main islands: Honshu, Shikoku and Kyushu. It is absent from Hokkaido, north of the Blakiston Line, and its northern limit is the Shimokita Peninsula at the tip of Honshu. Small islands such as Koshima, Kinkasan, Awaji and Shodoshima also hold troops. Three small islands, Omishima, Hiradoshima and Tanegashima, lost their monkeys in the middle of the 20th century. A 1989 survey estimated 114,431 wild monkeys in Japan.

In the south it lives in warm evergreen broadleaf forest, where the average temperature is about 20 degrees and rain reaches 3,000 millimetres a year. In the north it lives in cool deciduous forest, with an average of 10.9 degrees and about 1,500 mm of rain. It has been seen as high as 3,180 metres, but in winter it stays below about 1,800 m. Lowland forest was once its home too, but people cleared most of it long ago. Conifer plantations that replace natural forest make poor habitat.

In 1972 about 150 monkeys were moved from Kyoto to a ranch in the dry brushland of south Texas. Many died at first, but the survivors learnt to eat mesquite beans and cactus fruit and to avoid eagles, coyotes and rattlesnakes. By 1995 the troop numbered 500 to 600, and after hunters shot escaped monkeys in 1996 a 75-hectare sanctuary was set up near Dilley.

Diet and feeding

The Japanese macaque is an omnivore with a diet of more than 213 plant species. It eats fruit, seeds, nuts, leaves, flowers, buds, shoots and bark, plus fungi, ferns and roots. Animal food includes insects, spiders, crabs, molluscs, fish and birds' eggs. When better food is scarce it digs up roots and rhizomes or even eats soil.

The diet turns with the seasons. Fruit dominates in June and from September to November, and flowers and nectar in spring and midwinter. In winter the monkeys chew tough mature leaves, and in the north they fatten on nuts and fruit in autumn to survive the snow. On Kinkasan they live largely on Japanese barberry and zelkova, plants the island's sika deer will not eat. On Koshima a young female named Imo started washing sand off sweet potatoes in the sea, and the troop copied her. She also threw handfuls of wheat and sand into the water so the grain floated free, and that trick spread too.

Behaviour and social life

The macaque is diurnal and moves on all fours, with females spending more time in trees and males more on the ground. One study of daily time found 23.5 percent feeding, 22.8 percent travelling, 27.9 percent grooming others and 20.9 percent resting. It usually sleeps in trees, but on predator-free islands it sleeps on the ground. In winter the monkeys huddle together on their sleeping sites. They swim well, even in the sea, and one was recorded swimming more than half a kilometre.

Troops hold several matrilines, and wild troops average about 41 animals, from 10 to 161. A fed troop at Takasakiyama once reached 1,255. Females stay in their birth troop for life and rank below their mother but above their older sisters. Males leave by about five years old and may drift between troops or live alone. One male usually holds alpha rank, and his position changes when he dies or leaves or the troop splits. In 2021 a female named Yakei, aged nine, deposed the males and her own mother to lead a troop of 677 at Takasakiyama.

Grooming holds the troop together, and most of it passes between mothers and daughters. High-ranking families groom each other more and hold together better. At Jigokudani in Nagano the monkeys sit in a hot spring in winter. The habit began in the 1960s, after people lured them there to keep them off the crops. Bathing lowers their stress hormones, and top-ranking females hog the pool. Young monkeys roll snowballs and play with stones for no practical reason.

Communication and senses

Macaques coo while they feed or travel, and others coo back, which keeps the troop together. A softer girney call comes before grooming and calms a quarrel. Alarm calls warn of predators, and threat calls sound during fights, often from supporters on the sidelines. Researchers sort the calls into six groups, and more than half of them are peaceful. Troops in different regions call at different pitches, which scientists compare to human accents.

Faces and bodies speak too. A threatened monkey flattens its ears, raises its brows and opens its mouth to bare the teeth. A subordinate grimaces, smacks its lips, shows its rump or looks away. Displays of kicking, shaking and leaping rise in males during the mating season. Like other Old World monkeys, the macaque probably sees in full colour and relies on sight more than smell.

Reproduction and life cycle

Mating runs from autumn into winter, and births come in spring and summer, earlier in the north. A male and a female form a consortship, feeding, resting and travelling together for about 16 days on average. A female takes about four such partners in a season, and dominant males keep her longer. The female decides whether mating happens, and rank does not guarantee a male success. Her face and rump turn scarlet in the season, and she signals by looking back over her shoulder or walking backwards towards the male. Females also mount other females outside the season.

Gestation averages about 172 days, and the mother gives birth on the ground at the edge of the troop. One infant is the rule, and twins occur about once in 488 births. A newborn weighs a little over half a kilogram and clings to the belly for four weeks, then rides on the back. It tastes solid food at five to six weeks and can forage alone by seven weeks. Weaning starts at seven months and is complete by 18 months, though some infants nurse to 2.5 years. Childless females and, in some troops, older males help to carry and groom infants.

About 28.4 percent of infants die before their first birthday. Females mature at about 3.5 years and males at about 4.5, and a wild female has her first infant at five or six. Females in fed troops give birth more often than females in wild troops. The oldest wild female known reached 32 and the oldest male 28. A captive animal lived 38.5 years.

Predators and threats

The mountain hawk-eagle takes macaques from above, and the monkeys holler in alarm even at a gliding flying squirrel. Feral dogs once killed many, but the government now controls dog numbers. Raccoon dogs may take infants. The Japanese wolf was the natural predator until people wiped it out in the early 1900s. People are now the deadliest predator by far.

Since 1998 Japan has killed more than 10,000 macaques a year as crop pests, and recent culls pass 20,000. Biologists worry that the culls are shrinking the species' range. Conifer plantations that replace natural forest reduce its food. Before 1945 hunting for food and medicine and slash-and-burn farming pushed the range back. Males sometimes kill infants, which brings the mother back into breeding sooner.

Population and conservation

The IUCN lists the Japanese macaque as Least Concern, including both subspecies. It was once listed as Data Deficient because nobody knew whether the culls were sustainable. About 100,000 live in the wild, and a 1989 count gave 114,431. Hunting for sport or trade has been banned since 1947, but the same law allows the removal of nuisance animals. Numbers have grown since the 1940s thanks to protection, new forest and the loss of the wolf.

Populations have expanded in eastern Japan, while in the west some local troops have grown and others have vanished. Yakushima became a World Heritage Site in 1993, which protects the island subspecies but also brings tourists. The status of troops on high mountain slopes is unknown.

Relationship with humans

The macaque is the third worst crop pest in Japan, after wild boar and deer. It climbs ordinary fences and soon learns that scarecrows are harmless, so farmers need electric fences. In 2019 crop damage cost about 900 million yen. Monkeys wander into towns, and one lived in central Tokyo for months. In 2022 monkeys in the city of Yamaguchi attacked at least 50 people.

The species is one of the most studied primates in the world. Koshima island has been a study site since 1947, and every monkey there has been marked since 1952. Kawamura described the spread of potato washing there in 1959, and a garbled version later became the hundredth monkey myth. Macaques are used in neuroscience and drug testing, and culled animals go to medical and dental schools. Jigokudani Monkey Park, at 850 metres in Nagano, draws visitors up a 2 km path to watch the monkeys bathe. Monkeys habituate to people quickly, some within a week.

In culture and myth

The monkey runs through Shinto belief, folklore, art and everyday Japanese speech. Sarutahiko is a monkey-like god of crossroads who stands between heaven and earth. At Hiyoshi Taisha shrine the monkey god Sarugami serves as messenger of the mountain god Sanno. The three wise monkeys carved at Toshogu shrine in Nikko see, hear and speak no evil. The figure rests on a pun, since saru means monkey and echoes an old negative ending. In the Koshin folk faith the monkey is a go-between for people and gods. Following Chinese custom, monkeys were kept in stables to guard horses from sickness.

The peach boy Momotaro recruits a monkey, along with a dog and a pheasant, to fight the ogres. A second tale pits a crab against a monkey, and there the monkey plays the cheat. The warlord Toyotomi Hideyoshi, master of Japan by 1590, bore the nickname Kosaru, little monkey, because of his face. The proverb that even monkeys fall from trees means that anyone can slip. Edo-period artists such as Watanabe Kazan and Yoshitoshi painted macaques, and carvers shaped them into netsuke toggles. Trained monkeys still perform in sarumawashi shows, a trade that began with horse healers.