NORTHERN PIG-TAILED MACAQUE
Geographic Distribution and Habitat
Until recently, the northern pig-tailed macaque (Macaca leonina) was considered a sub-species of Macaca nemestrina (now commonly called the southern pig-tailed macaque), but is now recognized as a separate species. These northern pig-tailed macaques are found over a wide area of southeastern Asia including India, Bangladesh, Myanmar, Thailand, China, Laos, Cambodia, and Vietnam. The Brahmaputra River forms the northwestern boundary of their distribution.
They inhabit a wide range of habitats including both primary and secondary bamboo forests, deciduous, cloud, and evergreen forests and are found at elevations up to 6,562 feet (2,000 meters).
Much research prior to their taxonomic change refers to both southern and northern pig-tailed macaques simply as “pig-tailed macaques,” without specifying southern or northern populations, so some differences between the two species’ ecology and behavior is not well understood.
Size, Weight, and Lifespan
Northern pig-tailed macaques display sexual dimorphism in their size: males are larger with a head and body length of 19.6–23.6 in (50–60 cm) and a tail length of 6.3–9.8 in (16–25 cm), whereas females have a head and body length of 15.7–19.3 in (40–49 cm), and a tail length of 5.5–7.9 in (14–20 cm). Similarly, males weigh around 13.7–20 lb (6.2–9.1 kg), compared to females who weigh only 9.7–12.6 lb (4.4-5.7 kg).
These macaques live to approximately 26 years in the wild and in captivity have lived to be 35 years old.
Distinct differences in size or appearance between the sexes of an animal in addition to differences between the reproductive organs themselves.
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Northern pig-tailed macaques are large, thick-set monkeys with an olive-gray pelage that forms a darker brown crown on their heads. When standing quadrupedally, their broad chest and comparatively long legs mean they have an almost box-like shape. They have pinkish faces with patches of pale skin around the eyes and distinctive red lines extending from the outside corners of the eyes to the edge of the face. They have long hairs on their cheeks (the cheek ruff), which are especially prominent in adult males. Possibly their most distinctive feature is their short, thick tail, which is often arched over their backs. Their genitals and hindquarters are a darker red. Babies are born a darker brown and become lighter as they age. Compared to the southern pig-tailed macaque, northern pig-tailed macaques have a grayer pelage and more pronounced cheek ruffs.
This species is primarily frugivorous; fruits make up the majority of their diet. They are known to eat over 100 species of fruit, as well as other plant matter, bird eggs, and small animals, such as caterpillars.
Northern pig-tailed macaques in Thailand even eat some species of stinging caterpillars. In order to avoid being stung, the macaques first rub the caterpillars, either between their hands or with a leaf, to remove the stingers. After eating it, they rub their hands and mouth to remove any stray stingers. This is known as “extractive foraging” (processing food in some way to attain it/eat it safely) and is one of the more complex behaviors shown by primates.
Behavior and Lifestyle
These macaques are both terrestrial and arboreal, spending time both in the trees and on the ground; the amount of time spent in either can depend on the habitat. They can travel approximately 1.2 miles (2 km) a day throughout their home range, which tends to be around 0.17 sq miles (45 ha), although their ranging behavior changes with the season and fruit availability. Northern pig-tailed macaques are not considered to be territorial; they don’t engage in conflicts with neighboring groups at the borders of their home ranges, and these home ranges overlap extensively between different groups. They pick a sleeping site each night; sites are sometimes reused but usually not two nights in a row.
Northern pig-tailed macaques in Thailand are known to eat stinging caterpillars. They roll the caterpillars in their hands or a leaf prior to eating it to remove most of the stingers.
Their most distinguishing feature is probably their short, thick tail for which they are named, which usually arches over their back.
They play an important role in forest regeneration by dispersing seeds from over 100 species of plant.
Northern pig-tailed macaques live in multi-male, multi-female groups. In general, there are many more females per group than males. Group size can vary, averaging around 23 individuals, but can contain as many as 50 individuals.
The group members are organized into hierarchies, which can dictate much of daily life. Males will usually leave the group at sexual maturity to find a new group to integrate into. Females usually stay in their birth group, forming close matrilines of mothers, daughters, sisters, and aunts. Higher-ranking individuals usually have priority access to resources like food and mates, and both females and males engage in mounting behaviors to signal dominance toward group mates.
Macaques use a range of signals to communicate with one another and have a large repertoire of vocalizations, gestures, and facial expressions. Facial expressions in particular are important in a range of social contexts in macaque society. For example, pig-tailed macaques use the “silent bared teeth” expression either during conflicts, or when a more dominant monkey is nearby. This expression is analogous to a human smile and functions to avoid aggression by signaling subordination. They also use other facial expressions such as puckering of the lips, or raising of the eyebrows in a variety of social interactions.
The northern pig-tailed macaque is not a seasonal breeder and reproduction can happen throughout the year. Swelling of the skin around the females’ genitalia signals that they are in estrus and attracts the attention of males. Higher-ranking males have priority access to females in estrus, but low-ranking and non-group males can also father offspring. The females will give birth to a single infant after a gestation period of approximately 6 months. The infant will initially cling to its mother’s belly, before slowly becoming more independent as he or she ages.
Northern pig-tailed macaques play an important ecological role in their habitats. Their frugivorous diet means that they spread the seeds of dozens of plant species by swallowing, spitting, and dropping them throughout their range. For some plant species, the process of being digested by these macaques makes the seeds more likely to germinate after they return to the forest in the macaque’s feces, thereby highlighting the important role these monkeys play in regenerating forest habitat.
Conservation Status and Threats
The northern pig-tailed macaque is currently classified as Vulnerable, appearing on the International Union for Conservation of Nature’s Red List of Threatened Species (IUCN, 2020). While they are widespread throughout southeastern Asia, their numbers are decreasing, and they are Critically Endangered in Bangladesh.
Major threats to this species include the logging of forests and the building of roads and dams, which leads to habitat loss as well as to forest fragmentation and degradation. The loss of fruiting trees and sleeping sites makes this species particularly vulnerable. They are also hunted for meat, for the illegal pet trade, and for their bones, which are used in traditional medicine.
The northern pig-tailed macaque is listed under the Convention on International Trade in Endangered Species (CITES) Appendix II. It is also listed under various wildlife protection acts in Bangladesh, China, and India. While it occurs in several protected areas, more protections are needed for the species. In particular, habitat preservation is required to prevent further population decreases. No current monitoring programs are in place and specific area conservation plans are required, as well as education and awareness programs.
- Albert, A., Hambuckers, A., Culot, L., Savini, T., & Huynen, M. C. (2013). Frugivory and seed dispersal by northern pigtailed macaques (Macaca leonina), in Thailand. International Journal of Primatology, 34(1), 170-193.
- Albert, A., Savini, T., & Huynen, M. C. (2011). Sleeping site selection and presleep behavior in wild pigtailed macaques. American Journal of Primatology, 73(12), 1222-1230.
- DOBSON*, S. D. (2012). Coevolution of facial expression and social tolerance in macaques. American Journal of Primatology, 74(3), 229-235.
- José‐Domínguez, J. M., Savini, T., & Asensio, N. (2015). Ranging and site fidelity in northern pigtailed macaques (Macaca leonina) over different temporal scales. American Journal of Primatology, 77(8), 841-853.
- Trébouet, F., Reichard, U. H., Pinkaew, N., & Malaivijitnond, S. (2018). Extractive foraging of toxic caterpillars in wild northern pig-tailed macaques (Macaca leonina). Primates, 59(2), 185-196.
- Trébouet, F. (2019). Male Reproductive Strategies in Wild Northern Pig-Tailed Macaques (Macaca leonina): Testing the Priority-of-Access Model (Doctoral dissertation, Southern Illinois University at Carbondale).
Written by Jennifer Botting, PhD, September 2020