Japanese Macaque


Japanese Macaque (Macaca Fuscata)

The Japanese macaque (/məˈkɑːk/;[2] Macaca fuscata), is a terrestrial Old World monkey species native to Japan. They are also sometimes known as the snow monkey because they 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.[3][4] Individuals have brown-grey fur, red faces, and short tails. There are two subspecies.[5]

In Japan, the species is known as Nihonzaru (Nihon (ニホン) “Japan” + saru (ザル) “monkey”) to distinguish it from other primates, but the Japanese macaque is very familiar in Japan, so when Japanese people simply say saru, they usually have in mind the Japanese macaque.

Physical characteristics

The Japanese macaque is sexually dimorphic. Males weigh on average 11.3 kg (25 lb), while females average 8.4 kg (19 lb).[6] Macaques from colder areas tend to weigh more than ones from warmer areas.[7] Male average height is 570.1 mm (22.44 in) and female average height is 522.8 mm (20.58 in).[6] Their brain size is approximately 95 g (3.4 oz). Japanese macaques have short stumps for tails that average 92.51 mm (3.642 in) in males and 79.08 mm (3.113 in) in females.[7] The macaque has a pinkish face and posterior.[8] The rest of its body is covered in brown, greyish, or yellowish hair.[6] 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).[9]

Macaques mostly move on all fours. They are semi-terrestrial, with females spending more time in the trees and males spending more time on the ground. Macaques are known to leap. They are also great swimmers and have been reported to swim over half a kilometer.[6] The longevity for the macaque averages 6.3 years (at least for females).[10] However, they have been known to live much longer; males have lived up to 28 years and females up to 32 years.[11]


Group structure

Japanese macaques live in matrilineal societies,[6] and females stay in their natal groups for life, while males move out before they are sexually mature.[12] Macaque groups tend to contain a number of adults of both sexes. In addition, a 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.[13] Temporary all-male groups also exist, composed of those that have recently left their natal groups and are about to transfer to another group.[6] However, many males spend ample time away from any group[14]and may leave and join several groups.[6]

Males within a group 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.[15] Other ways in which status changes is when an alpha male loses his rank or when a troop splits, leaving a new alpha position open.[15] The longer a male is in a troop, the higher his status is likely to be.[16] Females also exist in a stable dominance hierarchy, and a female’s rank depends on her mother. Younger females tend to rank higher than their older siblings.[13][17] Higher-ranking matrilines have greater social cohesion.[18] Strong relationships with dominant females can allow dominant males to retain their rank when they otherwise would not.[19]

Females maintain both social relationships and hygiene through grooming. Grooming occurs regardless of climate or season.[20] Females which are matrilineally related groom each other more often than unrelated individuals.[21] Females will also groom unrelated females to maintain group cohesion and social relationships between different kinships in a troop.[22] Nevertheless, a female will only groom a limited number of other females, even if the group expands.[22] Females will also groom males, usually for hygienic purposes, but it can serve to attract dominant males to the group.[23] Mothers pass their grooming techniques to their offspring most probably through social rather than genetic means.[24]

Mating and parenting

A male and female macaque will form a pair bond and mate, feed, rest and travel together, and this typically lasts 1.6 days on average during the mating season.[25] Females enter into consortships with an average of four males a season.[26] Higher-ranking males have longer consortships than their subordinates.[25] In addition, higher-ranking males will try to disrupt consortships of lower-ranking males.[27] Females will attempt to mate with males of any rank. However, dominant males mate more as they are more successful in mate guarding.[28] The female decides whether mating will take place. In addition, dominance does not mean a male will successfully mate with a female.[6] Males may also temporarily join another troop during the mating season and mate with the females.[29] Females will also engage in same-sex mounting. Such behavior is likely because of hormones and females are mounted more often by other females than males.[30]

During the mating season, the face and genitalia of males redden and the tail will stand erect.[31] In addition, females’ faces and anogenital regions turn scarlet.[31] Macaques will copulate both on the ground and in the trees,[32] and roughly one in three copulations leads to ejaculation.[33] Macaques signal when they are ready to mate by looking backward over a shoulder, staying still, or walking backwards towards their potential partner.[34] A female will emit a “smooth-late-high coo”, or “squawk”, “squeak”, or produce an atonal “cackle” during copulation. Males have no copulatory vocalizations.

A macaque mother moves to the periphery of her troop to give birth in a secluded spot,[35] unless the group is moving, when the female will have to stay with it.[36] Macaques usually give birth on the ground.[6] Infants are born with dark-brown hair.[37] They will consume their first solid food at five to six weeks old, and can forage independently from their mothers by seven weeks.[37] A mother carries her infant on her belly for its first four weeks. After this time, the mother will carry her infant on her back, as well. Infants continue to be carried up to and past a year.[37] A mother and her infant tend to avoid other troop members, and the mother may socialize again very slowly.[38] However, alloparenting has been observed, usually by females which have not had infants of their own.[37] Male care of infants occurs in some groups, but not in others; usually, older males protect, groom, and carry an infant as a female would.[39]

Infants have fully developed their locomotive abilities within three to four months.[40] When an infant is seven months old, its mother discourages suckling; full weaning happens by its 18th month. In some populations, male infants tend to play in larger groups more often than females.[41] However, female infants have more social interaction than their male counterparts.[41] Males prefer to associate with other males around the same age, when they are two years old.[42] Female infants will associate with individuals of all ages and sexes.


During feeding or moving, Japanese macaques will often emit “coos”. These most likely serve to keep the troop together and strengthen social relations between females.[43] Macaques usually respond to coos with coos of their own.[44] Coos are also uttered before grooming along with “girney” calls. Variants of the “girney” call are made in different contexts.[45] This call also serves as appeasement between individuals in aggressive encounters.[46] Macaques have alarm calls for alerting to danger, and other calls to signal estrus that sound similar to danger alerts. Threat calls are heard during aggressive encounters and are often uttered by supporters of those involved in antagonistic interactions. The individual being supported will support the caller in the future.[47]

Intelligence and culture

The Japanese macaque is a very intelligent species. Researchers studying this species at Koshima Island in Japan left sweet potatoes out on the beach for them to eat, then witnessed one female, named Imo (Japanese for yam or potato), washing the food off with river water rather than brushing it off as the others were doing, and later even dipping her clean food into salty sea water.[48][49][50] After a while, others started to copy her behavior. This trait was then passed on from generation to generation, until eventually all except the oldest members of the troop were washing their food and even seasoning it in the sea.[48][49] She was similarly the first observed balling up wheat with air pockets, throwing it into the water, and waiting for it to float back up before picking it up and eating it free from dirt.[49][50] An altered misaccount of this incident is the basis for the “hundredth monkey” effect.[51]

The macaque has other unusual behaviours, including bathing together in hot springs and rolling snowballs for fun.[49] Also, in recent studies the Japanese macaque has been found to develop different accents, like humans.[52] Macaques in areas separated by only a few hundred miles can have very different pitches in their calls, their form of communication. The Japanese macaque has been involved in many studies concerning neuroscience and also is used in drug testing.[citation needed]


The Japanese macaque is diurnal. In colder areas, from autumn to early winter, macaques feed in between different activities. In the winter, macaques have two to four feeding bouts each day with fewer daily activities. In the spring and summer, they have two or three bouts of feeding daily.[32] In warmer areas such as Yakushima, daily activities are more varied. The typical day for a macaque is 20.9% inactive, 22.8% traveling, 23.5% feeding, 27.9% social grooming, 1.2% self-grooming, and 3.7% other activities.[53] Macaques usually sleep in trees, but will also sleep on the ground, as well as on or near rocks and fallen trees.[6] During the winter, macaques huddle together for warmth in sleeping grounds.[54] Macaques at Jigokudani Monkey Park are notable for visiting the hot springs in the winter to warm up.


The Japanese macaque is omnivorous and will eat a variety of foods. Over 213 species of plant are included on the macaque’s diet.[55] It also eats insects, bark and soil.[55] On Yakushima Island, fruit, mature leaves and fallen seeds are primarily eaten.[56] The macaque also eats fungi, ferns, invertebrates, soil and other parts of plants.[56] In addition, on Yakushima, their diets vary seasonally with fruits being eaten in the summer and herbs being eaten in the winter.[57] Further north, macaques mostly eat foods such as fruit and nuts to store fat for the winter, when food is scarce.[58] On the northern island of Kinkazan, macaques mostly eat fallen seeds, herbs, young leaves and fruits.[59] When preferred food items are not available, macaques will dig up underground plant parts (roots or rhizomes) or eat soil and fish.[55]

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