Macaca mulatta (Zimmermann 1780)

This adaptable species is highly promiscuous and both males and females mate with as many members of the opposite sex as possible. They travel in groups of between 8 and 180 individuals, usually with two to four times as many females as males. Breeding takes place whenever the seasons permit, with no defined period in non-seasonal areas. Females undergo a regular oestrus cycle of 26 – 29 days, but unlike many other macaques, the genital region swells and darkens in colour only slightly during the fertile period, and only in younger adult females (4). Gestation lasts around 165 days, and females give birth to a single young or, rarely, twins. The young is fed milk for a year, first clinging to the mother's belly, but riding on her back when older. After weaning, female juveniles may remain with the same group whereas males often disperse to another. Females become sexually mature between 2.5 and 4 years and males between 4.5 and 7 years. Females who reach ages of more than 25 years go through the menopause, eventually becoming infertile (6). The rhesus macaque shows dominance hierarchies in both sexes, but more so in males. The status of each individual is inherited from its mother. There may be confrontations between groups, but these are rare as weaker groups actively avoid stronger groups. Females within groups can be very loud, but rarely fight as they are usually closely related (4). All members of the group practise social grooming for pleasure, health and as a form of submission and appeasement. Appeasement is also shown by the fear grimace in which the lips are retracted to reveal the clenched teeth. Staring with the mouth open signifies threat and putting the tail vertically upwards indicates aggressive confidence. Infants attract their mother's attention by cooing, and adult females will also coo to attract a male. Males respond by lip-smacking as an invitation to mate (5). The diet of the rhesus macaque varies by region. They are omnivorous opportunists, feeding mainly on roots, herbs, insects, crop plants and small animals. They are good swimmers and will cross water to find food (4).

Continued research and monitoring of this species' behaviour, population status and range is necessary to foresee declines as a result of land use change across southern and Southeast Asia (1).

With an expressive face and active lifestyle, the rhesus macaque is a charismatic species. Its coat is pale brown above and fades on the underside, but the naked face and rump are bright red in adults (2). It has large cheek pouches which it uses to store food when foraging (5). Audebert, who named the rhesus macaque, did so after the Greek King of Thrace, Rhesos, but emphasized that it had no special relevance. Since, the name rhesus has been extended to the hereditary blood antigen 'Rh-factor' which was discovered on the red blood cells of rhesus macaques and was also found to be present in humans (4).

The rhesus macaque occupies an enormous range of habitats and climates, ranging from snow-covered mountains through dense forests to semi-desert and urban areas (1).

Still widespread across southern Asia, the rhesus macaque has nevertheless become locally extinct in some of its former range. It has been introduced into Florida, USA as well as to Cayo Santiago Island near Puerto Rico, and is kept in captivity in large numbers worldwide due to its common use in research (4). This species has even been a participant in space travel (4).

The rhesus macaque is classified as Lower Risk – near threatened (LR/nt) on the IUCN Red List 2004 (1) and is listed on Appendix II of CITES (3).

Whilst the rhesus macaque is threatened in the wild, a large captive population is maintained around the world for use in biological, psychological and medicinal research, especially for studies into perception, learning and behaviour. In the wild, the rhesus macaque is a generalist with great adaptability, allowing it to make the most of changes in land use. In India they are known for crop-raiding but their status as sacred animals in the Hindu religion prevents persecution by humans (4). Interspecies breeding is known to occur but appears to have no effect on the offspring's fertility, as other interspecies crosses usually do (6).