Macaca mulatta
(rhesus macaque)

Preferred Common Name

• rhesus macaque

Other Scientific Names

• Macaca mulata

International Common Names

• English: rhesus macaques; rhesus monkeys
• Spanish: mono resus
• French: macaque rhésus

• Domain: Eukaryota
•     Kingdom: Metazoa
•         Phylum: Chordata
•             Subphylum: Vertebrata
•                 Class: Mammalia
•                     Order: Primates
•                         Family: Cercopithecidae
•                             Genus: Macaca
•                                 Species: Macaca mulatta

Rhesus macaques are designated as “Chinese-derived” and “Indian-derived”, defined by their region of origin. Chinese-derived rhesus macaques are those specifically from China, and Indian-derived are those from India and surrounding countries; the two designations demonstrate distinct haplotypes (Smith and McDonough, 2005). Taxonomists have proposed ten subspecies on the basis of phenotypic and molecular characteristics, although many primatologists argue subspecies distinctions have been arbitrary (Fooden, 2000). The National Primate Research Center recognizes six subspecies: Macaca mulatta brevicauda, M. m. lasiota, M. m. mulatta, M. m. sanctijohannis, M. m. vestita and M. m. villosa (Cawthorn-Lang, 2005).

Rhesus macaques are Old World primates with brown or grey coats that are typically darker on the lower back and lighter above the waist and on the abdomen. The face and rump are hairless and pinkish in colour. They are sexually dimorphic. Adult males average 53.1 cm (1.74 ft) in height and females average 46.8 cm (1.54 ft). Average weights vary across populations, but males are typically 2-3 kg heavier than females (Maestripieri, 2010). Their movement is quadrupedal but they stand on their hind legs to enhance visibility. Their tails are relatively short and are typically relaxed but can be held up for various behaviours (e.g., dominance displays, breeding).

Introductions for Behavioural Research

In 1938, over 400 rhesus macaques were released on Cayo Santiago, Puerto Rico. The animals were introduced to the 15-ha island for behavioural research and to provide animals for biomedical research. While the animals are no longer used for biomedical research, the colony continues to be maintained for behavioural, physiological, ecological, demographic, and non-invasive biomedical research (Hernández-Pacheco et al., 2013; Hernández-Pacheco et al., 2016). The animals have thrived on the island, where they are provisionally fed daily. Despite the removal of over 4000 animals from 1984 to 2012, the population in 2016 was over 1500 individuals (Anderson, 2016).

Desecheo Island National Wildlife Refuge, Puerto Rico, was historically an important breeding habitat for thousands of breeding pairs of seabirds. A group of 57 rhesus macaques was introduced onto the island in 1966. The purpose of this introduction was to study behavioural adaptations to a novel habitat (Evans, 1989; Engeman et al., 2010). Seabird breeding had begun declining on the island after the introduction of rats in the early 1900s, but completely halted by 1970 due to the added pressure of predation by the macaques on eggs and nestlings (Evans, 1989). Several programmes to remove the macaques were implemented from1977 to 1985 (Evans, 1989). A final removal programme was implemented by the US Fish and Wildlife Service and Island Conservation in 2009 and was believed to be nearing eradication by 2015 (US Fish and Wildlife Service, 2011; US Fish and Wildlife Service, 2015).

Introductions for Biomedical Research

Rhesus macaques are the most frequently used primate species for biomedical research (Hannibal et al., 2017). Historically, the majority of these animals that were used for research were wild caught in India, however this practice was banned in India in 1978 (Crockett et al., 1996; Malik, 1989). As a result, US-based biomedical companies began free-ranging breeding populations on islands to provide animals needed for research. This subsequently led to rhesus macaque populations in Puerto Rico, Florida and South Carolina, USA.

In the 1960s-1970s, rhesus macaques and patas monkey (Erythrocebus patas) were introduced to the islands Cueva and Guayacán, off the southwestern coast of Puerto Rico. These animals escaped to the mainland of Puerto Rico by swimming the narrow channel between the islands and the mainland. Both species established and expanded populations on the mainland and by 2010 were estimated to occupy 600 km² of southwestern Puerto Rico (Engeman et al., 2010). Both species caused extensive agricultural damage due to crop-raiding. The Puerto Rico Department of Natural Resources and Environment and the United States Department of Agriculture began a collaborative project to eliminate the populations through euthanasia in 2008, and by 2014 had euthanized over 2000 patas monkeys and over 1000 rhesus macaques (López-Ortiz, 2016).

Charles River Laboratories, a subsidiary of Bausch and Lomb, introduced over 1300 rhesus macaques on Key Lois, an island in the Florida Keys in 1973. From 1978 to 1980, the company moved over 500 of the animals to Racoon Key, an island approximately 15 km north of Key Lois (Lehman et al., 1994; Johnson and Kapsalis, 1998). Like the introductions in Puerto Rico and South Carolina, the purpose of the introductions to these islands was to provide animals for biomedical research. Populations on both islands grew extensively resulting in destruction of mangroves (Kruer, 1996) and potentially decreased bird populations (Enge et al., 2002). The rhesus macacques were removed between 1999 and 2000 (Anderson et al., 2017).

Over 1400 rhesus macaques were introduced on Morgan Island, South Carolina, in 1979 to establish a breeding colony for biomedical research. The population thrived, reaching nearly 4000 individuals by the late 1980s (Taub and Mehlman, 1989). The colony continues as a source of research animals.

Introductions for Tourism

Rhesus macaques were introduced in to the areas surrounding the Silver River in central Florida, USA, in the 1930s. It was believed the animals would increase tourism in the area. Approximately six additional animals were released in the 1940s. By the 1970s the population was in excess of 150 animals. The land was purchased by the state of Florida and became Silver Springs State Park in 1985. By the mid-1980s there were nearly 400 rhesus macaques in Silver Springs State Park, and others had spread to the forests adjacent to the Ocklawaha River. Trapping was initiated in 1984 and continued intermittently to 2012, during which time approximately 1000 animals were trapped and removed. This practice caused extensive public controversy and was subsequently halted. The population in Silver Springs State Park was estimated to be approximately 115 individuals in 2013 and 175 in 2015, and unknown along the Ocklawaha River (Anderson et al., 2017).

Rhesus macaques were introduced to Titusville, Florida, USA, in 1976 after being released from a tourist attraction. There are records of some trapping and removal, but it is unclear how many individuals were removed. The population was last seen in the area in the early 1990s (Anderson et al., 2017).

Accidental and intentional introductions are associated with the tourism and biomedical industries.

Introduced rhesus macaques and patas monkeys (Erythrocebus patas) together caused extensive agricultural damage due to crop-raiding in southwestern Puerto Rico Engeman et al., 2010). During 2002-2006 total economic losses by commercial farmers to monkeys increased from US$1.13 million to over US$1.46 million per year. From this total, the economic losses due to farmers avoiding monkey damage by switching from fruit and vegetable crops to less rewarding land use (primarily hay or pastureland) alone increased from US$490,000 to US$1.33 million per year. In USDA (2008) it is estimated that the two species collectively caused US$300,000 in direct losses and $1 million in management costs in Puerto Rico. Economic costs elsewhere are associated with removal of animals where negative effects have been documented as environmental impacts.

In Florida, rhesus macacques introduced to Key Lois and Racoon Key consumed natural vegetation, including new growth of mangroves. The animals were reported to have led to the destruction of over 30 acres of red mangroves (Rhizophora mangle) on Key Lois (Kruer, 1996) and potentially decreased bird populations on Racoon Key (Enge et al., 2002). Legal actions resulted in a court-ordered mandate for the macaques to be removed from the islands. The animals were removed between 1999 and 2000 (Anderson et al., 2017).

An introduced population in Silver Springs State Park, Florida, was documented consuming quail eggs from artificial nests, indicating they may predate eggs of native birds (Anderson et al., 2016).

In South Carolina, tidal creeks surrounding the island were found to have elevated levels of Escherichia coli and faecal coliform as a result of the macaques (Klopchin et al., 2008).

In Puerto Rico, seabird breeding on Desecheo Island National Wildlife Refuge had begun declining after the introduction of rats in the early 1900s, but completely halted by 1970 due to the added pressure of predation by the macaques on eggs and nestlings (Evans, 1989). Observational studies conducted in 1969 and 1970 implicated them in the decline of the nesting populations of the red footed booby (Sula sula) and brown booby (Sula leucogaster) (Evans, 1989).

Rhesus macaques are the most frequently used primate species in biomedical research. Breeding colonies introduced in South Carolina, Puerto Rico and Florida, USA, have provided thousands of animals for research. All of these islands have documented negative environmental impact.   

Macaques are the natural host of the Herpes B virus. The virus is largely asymptomatic in macaques. The virus is spread by transmission of bodily fluid from an infected individual that is in a phase of actively shedding the virus to an uninfected individual. This can come from bites, scratches, exposure to urine or faeces, or sexual activity. Most macaques carry the virus by adulthood. There are no documented cases of humans contracting the virus from macaques in the wild. In laboratory settings, there have been 50 documented cases of humans contracting the virus from macaques, nearly half of which were fatal (CDC, 2016).

Rhesus macaques are the most frequently used primate in biomedical research. Populations introduced on islands produce animals for this purpose