RHESUS MONKEYS: CHARACTERISTICS, BEHAVIOR, RESEARCH

RHESUS MONKEYS

Rhesus monkeys (Scientific Name: Macaca mulatta) are a kind of macaque native to northern India and Pakistan but found throughout South Asua and Southeast Asia. Also known as Rhesus macaques, they can adapt to almost any environment. They streak through bazaars, walk through snow and are as comfortable in city streets as they are in the forest. They often live around temples and are regarded as sacred.

Rhesus monkeys are responsible for the naming of the hereditary blood antigen Rh-factor that was discovered in their red blood cells in 1940. Rh-factor is also found in humans. The mixing of Rh blood with non-Rh blood during blood transfusions or the later stages of pregnancy can result in potentially dangerous defense reactions by the human immune system. The name "rhesus" comes from Greek, Rhesos, the King of Thrace who assisted Priam at Troy. Audebert, the person who applied the name to the species, stated that it had no meaning. [Source: Joshua Seinfeld, Animal Diversity Web (ADW) /=]

Rhesus monkeys are not endangered. The IUCN Red List classifies them as a species of “Least Concern”. CITES classified them in Appendix II, which lists species not necessarily threatened with extinction now but that may become so unless trade is closely controlled. Rhesus monkeys may be fed on predators such as leopards, tigers, crocodiles and snakes. [Source: Joshua Seinfeld, Animal Diversity Web (ADW) /=]

Rhesus monkeys are a popular zoo animal because of its innate curiosity and active lifestyle. These monkeys are also used extensively for research. They are especially useful in biological, medicinal, and psychological research. Rhesus monkeys is most often used in psychological research when the emphasis is on perception, learning, or behavior. /=\

Rhesus monkeys are the commonest monkeys in India. They make up most of India’s 1.5 million monkeys. About half of them live in urban areas. Rhesus monkeys can live up to 30 years in the wild and in captivity. The average lifespan for females in captivity is 23.0 years. The average lifespan for males in captivity is 26.0 years. Rhesus monkeys have been extensively studied by Alison Richard of Yale.

Rhesus Monkey Habitat, Feeding and Where They Are Found

Populations of rhesus monkeys are most commonly found in a broad arc that stretches western Afghanistan, through India to northern Thailand. This species was wll represented in the past in southern China and Tibet, but humans have caused their decline over the past century or so. Because rhesus monkeys is often used for research, today populations are kept in captivity world wide. [Source: Joshua Seinfeld, Animal Diversity Web (ADW) /=]

Rhesus monkeys live in a wide range of habitats, including tropical forests, deserts, and grasslands, and are very adaptable. Some populations live in the hot, dry flatlands, while others, particularly in northern India and Pakistan, live in the Himalayas at elevations up to 3,000 meters and can endure cold winter temperatures that fall well below zero.

Some populations of rhesus monkeys have become accustomed to living with humans in urban, suburban and agricultural areas. Some small groups live in densely populated urban areas of northern India. These groups become so accustomed to living in areas occupied by people that if they are relocated they seek out other human-populated areas.

Rhesus monkeys are primarily omnivores (eat a variety of things, including plants and animals). Animal foods include birds, mammals, amphibians, reptiles, insects. Among the plant foods they eat are leaves, roots and tubers fruit. The dietary habits of rhesus monkeys can vary greatly depending upon where they live and the season. According to Animal Diversity Web: For example, rhesus that live in the mountain forests of northern Pakistan feed primarily on clovers during the summer, but during winter when snow covers the ground they are forced to switch to foods with lower nutritional values and higher fiber contents, such as pine needles and oak leaves. These monkeys seem to choose their environments carefully with respect to food resources. Even when they are forced to switch to lower quality food sources during the winter months they do not exhibit higher mortality rates, although they may lose a considerable percentage of their body weight. /=\

Rhesus Monkey Characteristics

native range of the rhesus monkey

Rhesus monkeys are small-to-medium-size primates. They have grizzled-brown fur on their back and slightly lighter color fur on their front side. The hair is short on the head. The face and buttocks of adults are red. They range in weight from four to 12 kilograms (8.81 to 26.43 pounds) and range in length from 45 to 64 centimeters (17.72 to 25.20 inches). The tail adds an additional 19 to 32 centimeters to the total length.

Rhesus monkeys exhibit sexual Dimorphism (differences between males and females). Males are bigger and heavier than females, weighing between 6.5 and 12 kilograms. Females weigh a only 5.5 kilograms on average.

Like all mammals rhesus monkeys are endothermic (use their metabolism to generate heat and regulate body temperature independent of the temperatures around them), homoiothermic (warm-blooded, having a constant body temperature, usually higher than the temperature of their surroundings) and have bilateral symmetry (both sides of the animal are the same). [Source: Joshua Seinfeld, Animal Diversity Web (ADW) /=]

Rhesus Monkey Behavior

Rhesus monkeys are arboreal (lives mainly in trees), terricolous (living in the ground or in the soil), diurnal (active during the daytime), motile (move around as opposed to being stationary), sedentary (remain in the same area), social (associates with others of its species; forms social groups), and have dominance hierarchies (ranking systems or pecking orders among members of a long-term social group, where dominance status affects access to resources or mates). Rhesus monkeys are very active and enjoy being in water and are good swimmers. [Source: Joshua Seinfeld, Animal Diversity Web (ADW) /=]

Rhesus monkeys can be very aggressive. Individuals often have missing ears, slashed faces and finger stumps that have resulted from fights and bites. When rhesus monkeys are involved in a threatening exchange they usually scream and screech and then look around to see who can support them. Fights between males can be quite nasty. One male was observed biting off the testicle of a rival, who in turn was observed mating the following day.

Rhesus monkeys are very loud. Young female rhesus monkeys have three main support calls: 1) a noisy blurred scream used when threatened by a dominant female; 2) a scream with a rising and falling pitch used when threatened by a subordinate; 3) a tonal, pulsed scream used when threatened by a member of the same matriarchal unit. Urgency is usually determined by the loudness and length of the calls. Mothers often respond to only the most distressed calls (unlike human mothers who often can't tell if their babies have a small or severe problem and respond equally in all in most cases).

Rhesus Monkey Group Behavior

Rhesus monkeys live in matriarchal societies, with mothers ranking above their daughters (and supporting them in fights) until they are very old. There is also a hierarchy of matriarchal units that is determined by relations between dominant female in each group. The situation in which family members will come to the aid of a female or not are usually defined by the ranking of the adversary. Rankings are sometime dramatically altered when females are claimed by disease or predators.

Male rhesus monkeys migrate between troops when they are young. Their status depends on their support from female members of their troop and their rank among males is derived from their fighting ability. Rhesus monkeys accept mentally retarded members to their group as they would a normal animal.

Rhesus monkey displaying its canine teeth

According to Animal Diversity Web: Rhesus monkeys live in groups of up to two hundred individuals. When a group's size reaches 80 to 100 members, a subgroup of females may split off to form a new group. Populations generally consist of a few unrelated males and many closely related females. Sometimes small groups form that consist of only males. Males usually leave the group in which they were born shortly after they reach sexual maturity. Offspring born to a mother and son, or to siblings, are very rare. Both males and females in a group show a preference for high ranking members of the opposite sex. [Source: Joshua Seinfeld, Animal Diversity Web (ADW) /=]

Dominance hierarchies exist in both sexes. This is far more evident in males, where competition for mates may occur regularly. The female members of a group usually live in complete harmony and rarely have violent interactions with one another. Although rhesus monkeys live in groups, they are not territorial (defend an area within the home range). Each group of individuals usually has its own sleeping space, but the territories of neighboring groups may overlap considerably. Confrontations between groups are rare. Usually when groups meet, the weaker group will avoid the stronger group. Any confrontations that arise are because of an uncertainty concerning strength and dominance. /=\

Rhesus Monkey Mating, Reproduction and Offspring

Rhesus monkey are polygynandrous (promiscuous), with both males and females having multiple partners. Although they show mate preferences, in general they are highly promiscuous. As they live in multi-male, multifemale groups, there are ample opportunities for individuals to copulate with multiple partners. Males are serial mounters, meaning that they mount a female multiple times before ejaculating. Males attract mates either by having high dominance status within the social group, or sometimes by being friendly (grooming, carrying infants, etc) to females. [Source: Joshua Seinfeld, Animal Diversity Web (ADW) /=]

Females rhesus monkeys are capable of producing one young per year under good conditions. Populations that live in areas where the winters are cold mate in the fall so that the young are born in the spring; those that live where seasonal changes are less pronounced have less well defined mating seasons. In populations that have distinct breeding seasons, testes swell to almost double their normal size during the breeding season. The disproportionately large testicles of male rhesus monkeys, and the increase in size of their testicles during the breeding season, is probably related to the number of times a male can copulate over a short period of time.

Females have an estrous cycle of 29 days, which is similar to the menstrual cycle of human females. They are receptive to copulation for between eight and 11 days during that cycle. When kept under uniform conditions in captivity, females maintain a steady estrus cycle of 26 to 28 days. Unlike many primate species, the estrus cycle of rhesus monkeys is not accompanied by major changes in the females' genital region. There is only minor swelling and redness around the genital area. To solicit copulations, females present their hindquarters to males. The skin of the perineal region becomes redded when the female is in estrus, and aliphatic acids are present, proving a potential chemical cue to their state of fertility. /=\

The gestation period ranges from 133 to 200 days, with the average being 165 days. Newborn macaques weigh between 400 and 500 grams. They nurse from their mother for about one year. Although young macaques typically cling to the fron of their mothers for the first few weeks of life, as their ability to keep themselves upright improves, they ride upon the mother's back. The position of the mother in the dominance hierarchy affects status of young. There is an extended period of juvenile learning. Females reach reproductive maturity at 2.5 to three years of age. Males reaching sexual maturity at 4.5 to seven years of age. Young inherit the territory of their parents, mother or father.

As is common to most primates, most of parental care is done by females. Mothers provide their young with protection, nutrition, grooming, and social experience from birth until independence. The role of males in parental care is hard to sort out. As social groups contain multiple males, and because females mate with many of these males, there is no certainty of paternity, so males don't even know which young are theirs. There may be some care given to young by close male friends of the mother. These males may be more likely to have sired the offspring. /=\

Rhesus Monkeys and Research

Sam, went into space in 1955

Rhesus monkeys were once the most common laboratory primate. In the 1950s, India was exporting 200,000 of these animals a year to Europe and the United States for biomedical research alone. For a number of reasons, the export was banned in 1978 and long-tailed macaques are now the most commonly used primate in medical research. Many monkeys used in laboratory work originate in China.

Scientists use rhesus monkeys to study HIV/AIDS drugs, research vaccines for rabies, smallpox and polio, and to study potential uses for embryonic stem cells. They have also been launched into space on test missions by the US and Russia.

Rhesus monkeys were used in pioneering studies of human blood. The Rh factor is named after them. A rhesus monkey has been genetically engineered to have jellyfish DNA in every one of its cells. The manipulation was done as step towards genetically manipulating human cells to fight disease. They are also widely exhibited at circuses and zoos and are a favorite of street performers with monkey acts.

In India, populations of rhesus monkeys have risen and fallen in respect to the attitudes of locals towards the animals. In the 1940s, when they were still revered as sacred animals there were an estimated 40 million of them. In the 1960s and 70s when they were preconceived as pest their numbers dropped to around 200,000. Now there are believed to be around a half million of them, with 85 percent of them living around people.

Rhesus Monkeys Can Recognize Themselves — and Count?

Unlike humans and great apes, rhesus monkeys don't realize when they look in a mirror that it is their own face looking back at them. But, according to a study published on January 8, 2015 in the journal Current Biology that doesn't mean they can't learn to recognize themselves in a mirror and once they do they may use mirrors spontaneously to explore parts of their bodies they normally don't see. "Our findings suggest that the monkey brain has the basic 'hardware' [for mirror self-recognition], but they need appropriate training to acquire the 'software' to achieve self-recognition," says Neng Gong of the Chinese Academy of Sciences. [Source: Phys.org, January 8, 2015]

In the late 1990s, Science News reported: “Rhesus monkeys can distinguish between varying numbers of items, from one to nine, and correctly order them from the smallest to the largest a study suggests. These results offer the strongest evidence to date that non-human primates wield numerical knowledge, say psychologist Herbert S. Terrace and psychology graduate student Elizabeth M. Brannon, both of Columbia University. [Source: Science News, July 11, 1998]

Since the monkeys make no obvious attempts to count on their fingers and maintain a humble silence in the face of researchers' questions, it remains difficult to pin down the mental tactics they use in determining that, for example, five diamonds represent a lesser quantity than six rectangles. The animals apparently have learned some type of numerical rule for ordering amounts from one to nine, Brannon theorizes. "We don't have direct evidence yet, but it seems likely that these monkeys, and other nonhuman primates, can count," she says.

Terrace and Brannon presented two male rhesus monkeys with a series of 35 displays, each consisting of four images, on a touch-sensitive computer screen. Each image portrayed a different object in numbers ranging from one to four. Images were arranged randomly, from left to right. They might show, for example, two bananas, one triangle, four apples, and three hearts. The size, surface area, shape, and color of objects were also changed randomly from one display to the next. The monkeys rapidly learned to touch pictures in ascending numerical order when they received food pellets for correct answers. After errors, the screen turned blank, and a few seconds later, a new set of pictures appeared.

Troublesome Urban Monkeys

Most of the troublesome monkeys in India are Rhesus monkeys. In India, they do significant damage to crops and gardens in many areas. Because they are viewed as sacred animals by Hindus, often little is done to stop them from stealing crops. As is true of most nonhuman primates, there is a high risk that they could carry diseases which affect humans.

Rhesus monkeys hang beside roads in the country and squat in the shade in train stations. They raid trash cans, steal ice cream cones from children, climb around on telephone and electric wires. Sometimes they get electrocuted when they touch frayed electric lines.

The monkeys often use temples as their home base because there they are protected and often fed and pampered. From the temples they radiate out. In the past many lived at temples with nearby forest in which they could retreat but now these temples have been swallowed up by urbanization and the only place they go is into the city.

"Once they get into human habited areas, initially they are shy," one monkey authority told AFP. "At that time people make the mistake of feeding the monkeys. Monkey's being smart, they soon give up their shyness and start demanding food. When they do that people don't take to them anymore. So the monkeys start entering houses, start opening refrigerators and take away food.”

Monkeys like urban areas because they have easy access to shelter, large trees, abundant food and water. In some cities their populations have exploded because the monkeys can get a hold of enough food to support such a large population. In some places the monkey are seriously obese. In other places their population are more stable apparently because their numbers are kept in check by disease and a limited food supply.

Monkeys run wild in Delhi. They make trouble by breaking into homes, stealing food from refrigerators, taking clothes off drying lines, damaging television antennas, making loud noises and destroying property. Sometimes they attack pedestrians. They like to break into offices at night and search through files for food. Monkey have even broken into the Presidential Palace and the defense ministry, destroying and stealing files. On his visit to the Amber Fort in Delhi, U.S. President Bill Clinton was ambushed by a bunch of monkeys. He discovered later they were attracted by his flower lei. "Once I deflowered they weren't interested in me," he said.

Image Sources: Wikimedia Commons

Text Sources: Animal Diversity Web animaldiversity.org ; National Geographic, Live Science, Natural History magazine, David Attenborough books, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Discover magazine, The New Yorker, Time, Reuters, Associated Press, AFP, Lonely Planet Guides, Wikipedia, The Guardian, Top Secret Animal Attack Files website and various books and other publications.

Last updated December 2024