Geographic Distribution and Habitat
Long-tailed macaques, also called crab-eating macaques and cynomolgus monkeys, are widely distributed across South Asia, including in Bangladesh, Brunei Darussalam, Cambodia, India (Nicobar Island), large areas of Indonesia, Lao PDR, Malaysia, Myanmar, the Philippines, Singapore, Thailand, Timor-Leste, and Viet Nam. This species inhabits a diverse range of habitats including coastal forests, mixed mangrove swamps, freshwater swamps, scrub grasslands, evergreen forests, bamboo forests, deciduous forests, and human settlements. It has also been introduced by humans to several areas outside of its native range, including China and the island of Mauritius. There is a zone of hybridization between the long-tailed macaque and the rhesus macaque (Macaca mulata) in mainland southeast Asia, which makes it hard to determine the northern boundary of this species.
There are at least 10 subspecies of the long-tailed macaque: the dark-crowned long-tailed macaque, Macaca fascicularis atriceps, the Burmese long-tailed macaque, M. fascicularis aureus, the Con Song long-tailed macaque, M. fascicularis condorensis, the long-tailed macaque, M. fascicularis fascicularis, the Simeulue long-tailed macaque, M. fascicularis fusca, the Karimunjawa long-tailed macaque, M. fascicularis karimondjawae, the Lasia long-tailed macaque, M. fascicularis lasiae, the Philippine long-tailed macaque, M. fascicularis philippensis, the Maratua long-tailed macaque, M. fascicularis tua, and the Nicobar long-tailed macaque, M. fascicularis umbrosus. Most of these sub-species’ populations are isolated and display few apparent differences apart from variations in pelage color, tail length, and cheek whiskers.
Size, Weight, and Lifespan
Long-tailed macaques were named for their remarkably long tails, which aid their balance and are longer than their head and body length, typically measuring around 19–23.5 in (50–60 cm). Their head and body length measures about 15–18.5 in (40–47 cm). These macaques show sexual dimorphism in size; males weigh approximately 10.5–15.5 lbs (4.8–7 kg), whereas females weigh approximately 6.5–8.5 lbs (3–4 kg).
Long-tailed macaques have an average lifespan of 15–30 years, with longer lifespans documented in captivity.
Long-tailed macaques have a pelage that ranges from gray to brown and is lighter at their bellies. At birth, infants have a much darker pelage, which gradually becomes lighter as they mature. Their faces are pink with yellow-brown eyes and large, square ears. Males are distinguished by their unique mustache, whereas females have a beard. Both sexes have cheek whiskers. These monkeys also have cheek pouches, which allows them to store food for later consumption.
Long-tailed macaques have a natural diet that consists of fruits, flowers, young leaves, and invertebrates. They are primarily frugivorous; they prefer to eat fruit but eat other items when fruit is not available. However, these monkeys are often found in close proximity to human populations and therefore the diet of different groups can vary depending on human provisioning or access to human refuse sites.
They also displays some feeding behaviors rarely seen in primates. Long-tailed macaques at two different sites in Indonesia have been observed catching and eating fish. They have also been observed using stones as tools to break into oysters and crabs and access the edible parts. Indeed, this species is sometimes referred to as the “crab-eating macaque” due to observations of coastal-living groups eating small crabs.
Unlike some other primates, this species does not usually swallow larger seeds from fruit. Their cheek pouches allow them to quickly take fruit from a tree, and then they chew fruits one by one and spit out the seeds while keeping the other fruits in their cheek pouches.
Behavior and Lifestyle
Since this species is so widespread, their behaviors and lifestyles vary across their range, from urban to wild environments. However, groups of long-tailed macaques in different habitats all spend high proportions of their day moving (around 18–30%), feeding (16–24%), and resting (16–20%). They also spend a lot of time engaged in social activities, such as grooming, play, and sexual behaviors, although time spent monitoring humans can decrease the amount of time they spend in social interactions in areas of their habitat that are impacted by humans.
They are primarily arboreal species, spending most of their time in trees, but will also travel on the ground. Their ranges can overlap with other primate species, and they are known to have agonistic encounters with other species, such as silvered leaf monkeys.
There are at least ten sub-species of long-tailed macaques.
These monkeys use stone tools to break into oysters and crabs, which may be a cultural behavior.
After conflicts between individuals, the victim and aggressor often engage in reconciliation.
Long-tailed macaques live in groups ranging in size from around 20 to over 100 individuals. Groups contain multiple adult males and females, though there are usually more adult females than males. Females remain in their natal groups and the hierarchy is based around matrilines (groups of highly related females). Males migrate into new groups when they reach sexual maturity and then throughout their lives. Younger males tend to migrate with group mates and may attempt to take over a new group at the top of the dominance hierarchy. Older males tend to migrate alone and “unobtrusively” enter the new group at a lower position in the hierarchy.
There are often within-group conflicts, but these macaques also show reconciliation after a conflict. Directly after a conflict, the aggressor or victim will often approach their opponent and display an affiliative behavior, which likely helps to reduce stress and further conflict after a fight.
Like many other primates, long-tailed macaques communicate using a range of behaviors, such as vocalizations, facial expressions, and gestures. They produce a wide range of vocalizations including barks, grunts, screams, and contact calls, among many others. These are used in a number of contexts including affiliative and agonistic interactions, during copulation, or in response to threats. Facial expressions and gestures such as baring their teeth, lip smacking, or genital presenting are also used in social interactions, often to signal appeasement.
The males at the top of the hierarchy are able to monopolize the females and thus reproduce more than lower-ranking males. They do this in part through “mate guarding,” which involves staying very close to a female and preventing other males from mating with her while she is fertile. Males recognize when a female is fertile through differences in her behavior, such as the female initiating copulation.
After a gestation period of around 163 days, the female will give birth to a single infant. Infanticide by adult males sometimes occurs in this species. This is beneficial to the male because the female becomes fertile again earlier and the male has a chance to reproduce more quickly. Males and females reach sexual maturity at around 4–5 years of age.
Primates often aid in seed dispersal through consuming seeds and then dispersing them via their faeces. However, these macaques do not ingest many seeds, instead spitting them out. Nonetheless, their cheek pouches mean that, although they do not ingest these seeds, they can still carry them some distance from the plant before spitting them out and therefore play a role in seed dispersal.
The International Union for Conservation of Nature (IUCN) lists the long-tailed macaque as Endangered (IUCN 2022), appearing on the IUCN’s Red List of Threatened Species. In the March 2022 assessment report it was noted that, in 2008, an IUCN primate specialist had proposed that the long-tailed macaque’s conservation status needed to be assessed more urgently and with a greater focus on the threats the species faced citing potential dramatic decline due to its heavy demand in trade, coupled with the rapid development in Southeast Asia. The scientist likened the trajectory of the species’ potential decline to that of the passenger pigeon, a highly populous North American bird species that in the mid-1800s was decimated to extinction in only 50 years during a cataclysmic surge of persecution and hunting. It was suggested that this could occur to the long-tailed macaque due to the high demand for the species in the national and international trade, and the levels of hunting and persecution they were experiencing. In 2022, the threats have increased as predicted and the species is now Endangered.
Hunting and trapping are occurring at unprecedented levels, as is persecution from human-macaque conflict. Long-tailed macaques are hunted for subsistence food and to fuel both the legitimate and illicit trade for biomedical research. Both price and demand for the monkeys as a trade commodity have skyrocketed during the COVID-19 pandemic, relative to the already regular and heavy pre-pandemic capture and trade. This alone is alarming given that primate species are well-documented to be sensitive to heavy hunting pressures.
In addition, the landscape of Southeast Asia continues to be deforested, reshaped, and degraded. Furthermore, it is noted that very few habitat countries have authoritative estimates of their long-tailed macaque populations, yet, in many places, these monkeys are being indiscriminately removed with the assumption that they are impervious to decline. There is a general lack of protection of the species across their range, although there are laws in place to protect them in several habitat countries.
The result could well be that the species may face irreversible population loss. Significant losses could be deterred with an urgent move towards better-structured wildlife monitoring and management programs that scientifically census, manage, and protect long-tailed macaques throughout Southeast Asia. Without such a change, there will be significant declines in the species’ population in the near future.
Finally, it is worth noting that this species faces both national (within-country) and international threats. For example, the demand for non-human primates in research is threatening the species. As such, the research industry needs to become accountable for the effects of its actions on wild non-human primate populations.
The IUCN estimates that the species has experienced a decline of at least 40% over the last three generations (approximately 40 years). They also suspect that the rates of decline are increasing as threats have increased and the species will experience at least a 50% decline in the coming three generations.
The long-tailed macaque is included in Appendix II of the Convention on International Trade in Endangered Species (CITES). It is also listed on wildlife protection acts in India and Bangladesh. However, there are few specific conservation efforts in place throughout its range, likely because it is still viewed as an “abundant” species. In particular, more research is needed on the various sub-species.
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Written by Jennifer Botting, PhD, July 2020, Conservation Status updated July 2022