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The Rhesus Macaque (Macaca mulatta), often called the Rhesus monkey, is one of the
best known species of Old World monkeys. It is a typical macaque, common throughout Afghanistan to
northern India and southern China. Rhesus
Macaques grow to a length of 64 centimetres, with tails reaching 30 centimetres. Males may weigh up to 6 kilograms, while females
are around half the weight. They are brownish to grey in colour with pinkish faces.
In science
The Rhesus Monkey is well known to science owing to its relatively easy upkeep in captivity, having been used extensively in
medical and biological research. It has given its name to the Rhesus
factor, one of the elements of a person's blood group. Rhesus Monkeys
were also used in the well-known experiments on maternal deprivation carried out in the 1950s by
comparative psychologist Harry F. Harlow. NASA launched Rhesus Macaques into space during the 1950s
and 60s.
In January of 2000, the Rhesus Macaque
became the first cloned primate with the
birth of Tetra. January
2001 saw the birth of ANDi, the first transgenic primate; ANDi carries foreign genes originally from a jellyfish.
Much of our knowledge of the natural behaviour of Rhesus Macaques comes from studies carried out on a colony established by
the Caribbean Primate Research Center of the University of Puerto Rico on the island of Cayo Santiago, off Puerto Rico. There are no predators on the island, and humans are not permitted to
land except as part of the research programmes. The colony is provisioned to some extent, but about 50% of its food comes from
natural foraging
In nature
Inhabiting arid, open areas, Rhesus Macaques may be found in grasslands, woodlands, and in mountainous regions up to 2,500
metres in elevation. They are good swimmers and are said to enjoy the activity. Rhesus Macaques are noted for their tendency to
move from rural to urban areas, coming to rely on handouts or refuse from humans. They have become pests in some areas, perceived
as a possible risk to public health and safety.
Diurnal animals, Rhesus Macaques are both arboreal and terrestrial; they are mostly herbivorous and feed on leaves and pine needles, roots, and the occastional insect or small animal. The monkeys
have specialized pouch-like cheeks, allowing them to temporarily horde their food. The gathered morsels are eaten sometime later,
in safe surroundings.
Behaviour and reproduction
Like other macaques, the Rhesus troop comprises a mixture of males and females. The troop may contain up to 180 individuals,
but 20 is the average. Females may outnumber the males by a ratio of 4:1. The social hierarchy is also matriarchal, rank
dependent on lineage to the lead female. Care of young and territory surveillance duties are shared amongst the troop. While
females are more or less placid, males are typically rowdy between themselves. Rhesus Macaques are characterised as vociferous
monkeys. Monkeys that discover food will normally advertise the fact by specific calls, though it has been claimed that young or
subordinate monkeys will sometimes seek to avoid doing so if their discovery has gone unobserved.
Mating is not confined to a specific season. Gestation may last from 135-194
days. Females are mature by three years of age, and males at four. They may live for 30 years or more.
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