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By Joshua Seinfeld
Geographic Range
Populations of rhesus monkeys (Macaca mulatta) are most commonly found in western Afghanistan, through India to northern Thailand. This species was abundant historically in southern China and Tibet, but humans have caused drastic decline of populations in these areas over the last sixty years. Because M. mulatta is often used for research, today populations are kept in captivity world wide.
(Nowak, 1991; Parker, 1990; Wilson and Reeder, 1993)
Biogeographic Regions:
palearctic 
(native ); oriental (native ).
Habitat
(9840 ft)
Macaca mulatta lives in a wide range of habitats, and shows a great deal of adaptability. Some populations live in flatlands, while others, in northern India and Pakistan, live in the Himalayas at elevations up to 3,000 m. These primates are able to aclimate to a variety of climatic extremes, from the hot, dry temperatures found in deserts, to cold winter temperatures which fall to well below the freezing point.
In addition to living in the wilderness, some populations of M. mulatta have become accustomed to living alongside humans. Occasionally, small groups can be found living in the densely populated urban areas of northern India. Groups of rhesus monkeys that become used to living in areas occupied by people usually search out other human-populated areas if people attempt to relocate them away from civilization.
(Nowak, 1991; Parker, 1990)
These animals are found in the following types of habitat:
temperate ; tropical ; terrestrial .
Terrestrial Biomes:
desert or dune ; savanna or grassland ; forest ; mountains .
Other:
urban ; suburban ; agricultural .
Physical Description
(8.8 to 26.4 lbs)
(17.72 to 25.2 in)
These smallish monkeys have grizzled-brown fur dorsally, with the fur on the ventrum being slightly lighter in color. The hair is short on the head. The face and buttocks of adults are red.
Length varies in this species, ranging between 45 and 64 cm. The tail adds an additional 19 to 32 cm to the total length. Males are somewhat heavier than females, weighing between 6.5 and 12 kg. Females weigh a mere 5.5 kg on average. (BBC, 2005)
Some key physical features:
endothermic ; homoiothermic; bilateral symmetry .
Sexual dimorphism: male larger.
Reproduction
Females 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; those that live where seasonal changes are less pronounced have less well defined mating seasons
Although rhesus monkeys 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.
Female rhesus monkeys have a sexual cycle of 29 days. They are receptive to copulation for between 8 and 11 days during that cycle. 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.
Rhesus monkeys are serial mounters, meaning that males 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. (Hrdy and Whitten, 1987)
Mating systems:
polygynandrous (promiscuous) .
The breeding season varies widely amongst populations. Populations that live in areas where the winters are cold mate in the fall so that the young are born in the spring. Macaca mulatta that live where seasonal changes are less pronounced have less well-defined mating seasons.
The gestation period is around 165 days, and almost all pregnancies results in birth of a single young. 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 M. mulatta is not accompanied by major changes in the females' genital region. There is only minor swelling and redness around the genital area.
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.
(Buscovitch, 1993; Nowak, 1991; Parker, 1990)
Newborn macaques weigh between 400 and 500g. They nurse from their mother for about 1 year. Although young macaques typically cling to their mother's ventrum for the first few weeks of life, as their ability to keep themselves upright improves, they ride upon the mother's back. Females reach nreproductive maturity at 2.5 to 3 years of age. Males take longer to complete the transition to adulthood, reaching sexual maturity at 4.5 to 7 years of age. (Nowak, 1991)
Key reproductive features:
iteroparous ; seasonal breeding ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous ; post-partum estrous.
As is common to most primates, the bulk of parental care falls to females. Mothers provide their young with protection, nutrition, grooming, and social experience from birth until independence.
The role of males in parental care is somewhat confusing. Because 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.
Parental investment:
altricial ; pre-fertilization (provisioning, protecting: female); pre-hatching/birth (provisioning: female, protecting: female); pre-weaning/fledging (provisioning: female, protecting: female); pre-independence (protecting: female); post-independence association with parents; extended period of juvenile learning; inherits maternal/paternal territory; maternal position in the dominance hierarchy affects status of young.
Lifespan/Longevity
[External Source: Max Planck Institute for Demographic Research]
Rhesus monkeys can live up to 30 years.
Behavior
Rhesus monkeys are highly active and very loud. They enjoy being in water and are good swimmers. They 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.
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. 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.
(Buscovitch, 1993; Dotta, 1988; Nowak, 1991; Tate, 1947)
Communication and Perception
Communication in all monkeys involves a variety of visual signals (such as body postures and facial expression), tactile communication (such as grooming, playing and fighting), vocalizations, and scent cues.
Food Habits
The dietary habits of rhesus monkeys can vary greatly depending upon where they live. Macaca mulatta is omnivorous, and often eat roots, herbs, fruits, insects, crops, and small animals. The diet can also vary with the season. 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.
(Macdonald, 1984; Nowak, 1991; Parker, 1990)
Primary Diet:
omnivore .
Animal Foods:
birds; mammals; amphibians; reptiles; insects.
Plant Foods:
leaves; roots and tubers; fruit.
Predation
Primates are often wary of potential predators. It is likey that large carnivores, raptors, and snakes could prey upon these macaques.
Ecosystem Roles
The role of these animals in their ecosystems has not been fully described. Because of their frugivory, rhesus monkeys may help to disperse seeds. As a prey species, they may affect predator populations.
Economic Importance for Humans: Negative
In India, rhesus monkeys 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.
(Nowak, 1991; Parker, 1990)
Ways that these animals might be a problem for humans:
injures humans (bites or stings); crop pest.
Economic Importance for Humans: Positive
Macaca mulatta is 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. Macaca mulatta is most often used in psychological research when the emphasis is on perception, learning, or behavior.
(Nowak, 1991; Parker, 1990)
Ways that people benefit from these animals:
source of medicine or drug ; research and education.
Conservation Status
IUCN Red List: [link]:
Lower Risk - Near Threatened.
US Federal List: [link]:
No special status.
CITES: [link]:
Appendix II.
IUCN considers this species Lower risk/ near threatened.
Other Comments
The common name, rhesus monkey, is responsible for the naming of the hereditary blood antigen Rh-factor that was discovered on 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.
(Nowak 1991)
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.
(Jaeger 1972)
For More Information
Find Macaca mulatta information at
Contributors
Joshua Seinfeld (author), University of Michigan.
Nancy Shefferly (editor), Animal Diversity Web Staff.
