Distribution
Rhesus macaques (Macaca mulatta) are native to Asia and have the widest distribution range of all monkey species. Their habitat stretches from Afghanistan, through India, Thailand, and Vietnam, to China. Thanks to their adaptability, they live in both the winter-cold high mountain regions of the Himalayas and the dry, hot plains.
Physical Characteristics
Rhesus macaques have a gray-brown fur coat, and their hairless faces range from pink to reddish. Males and females differ in weight and size, with males significantly larger and heavier (up to 14 kg with a maximum head-body length of 66 cm). Additionally, males have noticeably larger canine teeth.
Diet
Rhesus macaques are omnivores. Their diet primarily consists of plant material, but they also consume insects, spiders, crustaceans, and bird eggs. In wetland areas, they also catch and eat fish. Near human settlements, they frequently plunder fields and gardens or rummage through garbage cans for food.
Habitat and Lifestyle
Rhesus macaques prefer open scrubland, forests, and parks as their habitat. Some clans also inhabit rocky areas and coastal marshes. Due to their high adaptability, they are increasingly found with close range to humans, especially where their natural habitats have been restricted. In South Asia, particularly in India, they can be seen in village settlements, temple complexes, and even large cities. Rhesus macaques are highly vivacious and active animals. They live in groups of 20 to 200 individuals and may stay on the ground or in trees, depending on their habitat. They spend most of their day foraging for food. Rhesus macaques walk on all fours on the ground but are also adept climbers and jumpers. Additionally, they are good swimmers and enjoy bathing. The size of their home ranges varies widely, spanning from several hundred meters to several kilometers. Although Rhesus macaques live in groups, they are not very territorial. The territories of neighboring groups can overlap significantly, but conflicts are rare, as the outnumbered group usually retreats quickly during confrontations.
Social Behavior and Reproduction
Rhesus macaques groups consist of several males, females, and juveniles. Hierarchies develop in both sexes, with females forming more stable and enduring hierarchies than males. Females remain in their birth group, while males migrate upon reaching sexual maturity and form smaller bachelor groups. Rhesus macaques are promiscuous, with mating preferentially occurring between individuals of equal rank within the group. Females reach sexual maturity around three and a half years, while males mature at about five and a half years. Mating times vary according to habitat. Rhesus monkeys living in winter-cold regions prefer to mate in the fall, ensuring that their young are born in spring. In lowland areas, reproduction is tied to the monsoon season, with births peaking before and after the monsoon (March–June and September–October). After a gestation period of about 166 days, females give birth to a young weighing between 450 and 500 grams. In the first few weeks, the infant is primarily carried on the mother's belly or back and is intensively cared for. By two weeks, it begins to eat solid food, and after six months, it becomes largely independent.
Rhesus Macaques in Research
Rhesus macaque have long been used as research animals due to their physiological and anatomical similarities to humans. In 1940, the Rhesus factor was discovered in their blood, a significant finding that later found in humans, too. This important finding has since prevented life-threatening immune reactions during blood transfusions and pregnancy. In the 1950s, researchers used Rhesus monkeys in experiments to develop the poliovirus vaccine, which now protects millions from infection. However, this led to a significant decline in their population due to mass exports from India to various countries. It wasn't until the late 1970s that the Indian government completely halted the export of monkeys, allowing the populations to recover. Today, Rhesus macaques for research are bred in specialized facilities like the German Primate Center (DPZ) to prevent them from being removed from their natural habitats while adhering to high sanitary standards. Globally, Rhesus monkeys are primarily used in infection research, drug development, and neuroscience studies. In 2007, the results of the DNA sequencing of the Rhesus monkey genome were published in the journal Science. After humans and chimpanzees, Rhesus monkeys are the third primate species to be fully sequenced, revealing a 93.5% similarity in DNA to humans.