AppearanceThe body length of the adult, which varies among subspecies, is 38–55 cm with relatively short arms and legs. Males are considerably larger than females, weighing 5–9 kg compared to the 3–6 kg of females. The tail is longer than the body, typically 40–65 cm , which is used for balance when they jump distances up to 5 m . The upper parts of the body are dark brown with light golden brown tips. The under parts are light grey with a dark grey/brown tail. Crab-eating macaques have backwards-directed crown hairs which sometimes form short crests on the midline. Their skin is black on their feet and ears, whereas the skin on the muzzle is a light grayish pink color. The eyelids often have prominent white markings and sometimes there are white spots on the ears. Males have a characteristic mustache and cheek whiskers, while females have only cheek whiskers. Crab-eating macaques have a cheek pouch which they use to store food while foraging. Females show no perineal swelling.
Naming''Macaca'' comes from the Portuguese word ''macaco'', which was derived from ''makaku'', a Fiot word . The specific epithet ''fascicularis'' is Latin for a small band or stripe. Sir Thomas Raffles, who gave the animal its scientific name in 1821, did not specify what he meant by the use of this word.
In Indonesia and Malaysia, ''M. fascicularis'' and other macaque species are known generically as ''kera'', possibly because of their high-pitched cries.
The crab-eating macaque has several common names. It is often referred to as the long-tailed macaque due to its tail, which is often longer than its body. The name crab-eating macaque refers to its being often seen foraging beaches for crabs. Another common name for ''M. fascicularis'' is the cynomolgus monkey, which literally means dog-skin or dog-hide monkey; this name is commonly used in laboratory settings.
DistributionThe crab-eating macaque lives in a wide variety of habitats, including primary lowland rainforests, disturbed and secondary rainforests, shrubland, and riverine and coastal forests of nipa palm and mangrove. They also easily adjust to human settlements; they are considered sacred at some Hindu temples and on some small islands, but are pests around farms and villages. Typically, they prefer disturbed habitats and forest periphery. The native range of this species includes most of mainland Southeast Asia, from extreme southeastern Bangladesh south through Malaysia, and the Maritime Southeast Asia islands of Sumatra, Java, and Borneo, offshore islands, the islands of the Philippines, and the Nicobar Islands in the Bay of Bengal. This primate is a rare example of a terrestrial mammal that violates the Wallace line.
StatusThe crab-eating macaque has the third-largest range of any primate species, behind only humans and rhesus macaques. The IUCN Red List categorizes the species as Least Concern, and CITES lists them as Appendix II . A recent review of their populations suggests a need for better monitoring of populations due to increased wild trade and rising levels of human-macaque conflict, which are reducing overall population levels despite the species being widely distributed.
Each subspecies faces differing levels of threats, and too little information is available on some subspecies to assess their conditions. The ''M. f. umbrosa'' subspecies is likely of important biological significance and has been recommended as a candidate for protection in the Nicobar Islands, where its small, native population has been seriously fragmented, and is listed as vulnerable on the IUCN Red List. The Philippine long-tailed macaque is listed as near threatened, and ''M. f. condorensis'' is vulnerable. All other subspecies are listed as data deficient and need further study; although recent work is showing ''M. f. aurea'' and ''M. f. karimondjawae'' need increased protection. One concern for conservation is, in areas where ''M. fascicularis'' is not native, their populations need to be monitored and managed to reduce their impact on native flora and fauna.
BehaviorIn Thailand and Myanmar, crab-eating macaques use stone tools to open nuts, oysters, and other bivalves, and various types of sea snails along the Andaman sea coast and offshore islands.
Another instance of tool use is washing and rubbing foods such as sweet potatoes, cassava roots, and papaya leaves before consumption. Crab-eating macaques either soak these foods in water or rub them through their hands as if to clean them. They also peel the sweet potatoes, using their incisors and canine teeth. Adolescents appear to acquire these behaviors by observational learning of older individuals.
HabitatThe crab-eating macaque lives in a wide variety of habitats, including primary lowland rainforests, disturbed and secondary rainforests, shrubland, and riverine and coastal forests of nipa palm and mangrove. They also easily adjust to human settlements; they are considered sacred at some Hindu temples and on some small islands, but are pests around farms and villages. Typically, they prefer disturbed habitats and forest periphery. The native range of this species includes most of mainland Southeast Asia, from extreme southeastern Bangladesh south through Malaysia, and the Maritime Southeast Asia islands of Sumatra, Java, and Borneo, offshore islands, the islands of the Philippines, and the Nicobar Islands in the Bay of Bengal. This primate is a rare example of a terrestrial mammal that violates the Wallace line.
ReproductionAfter a gestation period of 162–193 days, the female gives birth to one infant. The infant's weight at birth is about 320 g . Infants are born with black fur which will begin to turn to a yellow-green, grey-green, or reddish-brown shade after about three months of age. This natal coat may indicate to others the status of the infant, and other group members treat infants with care and rush to their defense when distressed. Immigrant males sometimes kill infants not their own, and high-ranking females sometimes kidnap the infants of lower-ranking females. These kidnappings usually result in the death of the infants, as the other female is usually not lactating. A young juvenile stays mainly with its mother and relatives. As male juveniles get older, they become more peripheral to the group. Here they play together, forming crucial bonds that may help them when they leave their natal group. Males that emigrate with a partner are more successful than those that leave alone. Young females, though, stay with the group and become incorporated into the matriline into which they were born.
Male crab-eating macaques groom females to increase the chance of mating. A female is more likely to engage in sexual activity with a male that has recently groomed her than with one that has not.
FoodCrab-eating macaques typically do not consume crabs; rather, they are opportunistic omnivores, eating a variety of animals and plants. Although fruits and seeds make up 60 - 90% of their diet, they also eat leaves, flowers, roots, and bark. They sometimes prey on vertebrates , invertebrates, and bird eggs. In Indonesia, the species has become a proficient swimmer and diver for crabs and other crustaceans in mangrove swamps. A study in Bukit Timah, Singapore recorded a diet consisting of 44% fruit, 27% animal matter, 15% flowers and other plant matter, and 14% food provided by humans.
This species exhibits particularly low tolerance for swallowing seeds. Despite their inability to digest seeds, many primates of similar size swallow large seeds, up to 25 mm , and simply defecate them whole. The crab-eating macaque, though, spits seeds out if they are larger than 3–4 mm . This decision to spit seeds is thought to be adaptive; it avoids filling the monkey’s stomach with wasteful bulky seeds that cannot be used for energy.
Although the species is ecologically well-adapted and poses no threat to population stability of prey species in its native range, in areas where the crab-eating macaque is not native, it can pose a substantial threat to biodiversity. Some believe the crab-eating macaque is responsible for the extinction of forest birds by threatening critical breeding areas as well as eating the eggs and chicks of endangered forest birds.
The crab-eating macaque can become a synanthrope, living off human resources. They are known to feed in cultivated fields on young dry rice, cassava leaves, rubber fruit, taro plants, coconuts, mangos, and other crops, often causing significant losses to local farmers. In villages, towns, and cities, they frequently take food from garbage cans and refuse piles. The species can become unafraid of humans in these conditions, which can lead to macaques directly taking food from people, both passively and aggressively.
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