Geographic Distribution and Habitat
Arunachal macaques were first described in 2005, after primatologists discovered a previously undescribed population of macaques during an expedition in eastern India. Arunachal macaques are native to India, and are known to live only in Arunachal Pradesh, a state far to the northeast of the country. Nestled in the eastern Himalayan biodiversity hotspot, the northeastern portion of India boasts the highest diversity of primates in the country, and Arunachal Pradesh has arguably the richest terrestrial biodiversity in the region. This macaque species has never been reported living outside of India, although it is suspected that some populations may live in nearby Tibet and Bhutan. The Brahmaputra River borders the species’ range to the east, and separates it from the closely related eastern Assamese macaque.
Arunachal macaques are the highest-dwelling of all the Indian macaques, living exclusively in alpine regions with altitudes between 6,500 and 11,500 feet (2,000–3,500 m). They reside in broadleaf forests and are relatively tolerant of habitat disturbance, adjusting to degradation such as deforestation and agriculture conversion. In one population survey, more than 75% of Arunachal macaques lived in human-modified landscapes, such as close to villages and crop fields. More than half of the surveyed individuals lived in degraded forests that have been subject to disturbance such as felling, livestock grazing, and leaf litter collection.
Size, Weight, and Lifespan
There is only one documented case of an Arunachal macaque having been measured or weighed. This adult male weighed 33 lbs (15 kg) and was 32 inches (82 cm) long including the tail, which was 10 inches (26 cm) long. Adult females are slightly smaller than this. It is unknown what their average lifespan is, though it is likely similar to those of other macaques: between 20 to 30 years in the wild and up to 40 years in captivity.
Arunachal macaques are large, stocky monkeys, with long arms and legs and a relatively short tail. Their coats are a yellowish-brown, becoming paler on the torso and limbs, and their faces are a pinkish tan. Like most primates, they have large forward-facing eyes that allow for depth perception. They are sexually dimorphic, with males being bigger and sporting longer skulls and larger canine teeth than females. Juveniles look similar to adults, although their tail is relatively hairless and whip-like. There may be very minor seasonal variations in coat color.
Arunachal macaques are almost, but not quite, strict herbivores (plant-eaters). Their diet consists of about 30 different plant species in total, although most of their diet is composed of only a few plants—in the winter, two species comprise a full 75% of their diet. One of these is Erythrina variegata, a climbing herb that comprises 72% of feeding time in the winter and 19% in spring. They eat mainly leaves, but sometimes also eat fruits, flowers, stems, or bark, the latter of which is mainly eaten in winter. Besides plants, Arunachal macaques occasionally supplement their diet with small invertebrates and mud, which contains vital minerals such as calcium, sodium, and iron.
Behavior and Lifestyle
Arunachal macaques are diurnal (active in daylight hours) and quadrupedal (walk on all fours). While terrestrial during the day, feeding on the ground, they are still at home in trees, preferring to nest about 50 feet (15 m) above the ground at night. Most of an Arunachal macaque’s day is spent eating or foraging: in summer this comprises 29–51% of daily activity, and in the winter this number can rise up to 66%. During the summer, Arunachal macaques travel long distances in search of food. In winter, the macaques prefer to subsist on larger quantities of lower-quality food, which they don’t need to travel as far to reach. This allows them to conserve energy. Arunachal macaques rest more than similar species, another energy-saving measure. This is likely due to the colder temperatures and higher altitudes of their habitat, making energy conservation a high priority. Resting during the summer may also involve sun basking, an activity that may take up a large portion of their day.
The species name munzala comes from the local name in Dirang Monpa mon zala, literally meaning “deep forest monkey.” Dirang Monpa is a dialect spoken by the Monpa people, a nomadic Buddhist tribe of Arunachal Pradesh, India.
Group size ranges greatly, from 5 to 60 individuals, with an average group size of around 20. They live in multi-male multi-female groups composed of adults, juveniles, and infants. There is very little aggression within the group, and what little there is is typically limited to threat displays, which are more common in winter when food is scarce. Groups bond in the form of grooming, which occurs between adults of the same sex and juveniles to adult females. Arunachal macaques have a matrilineal group structure, with the ranking of an individual’s mother likely helping to determine its future status. Groups have well-defined ranges, which sometimes overlap with other groups, and range in area from 17 to 136 acres (7–55 ha). Intergroup relations are generally peaceful.
In general, macaques communicate vocally, visually, and tactilely. There are no documented examples of vocal communication in Arunachal macaques, although it almost certainly occurs. Visual communication observed in Arunachal macaques include facial expressions, body posture, and branch-shaking. These activities usually communicate dominance or submission. Tactile communication is mainly expressed in the form of grooming, a social bonding activity.
Specifics of reproduction and parental care, such as number of offspring, age at weaning, and age of sexual maturity, are unfortunately not definitively known for the Arunachal macaque. However, inferences can be made based on observations and from closely related species. The low infant-to-adult ratios observed in Arunachal macaque groups suggests that they likely don’t reproduce every year; it is more likely that an adult female gives birth every two years. All other macaque species give birth to one or two offspring at a time, so that is likely true for the Arunachal macaque as well. Gestation time for other macaques varies between 150 and 190 days.
Like all primates, Arunachal macaques have altricial young, meaning that their offspring need a significant amount of parental care to survive. For macaques, the mother is the main provider of this care, taking on the role of nursing, carrying, grooming, teaching, and protecting the baby until he or she is independent. In some macaque species, older sisters of the offspring may help to care for the child, as may other adult females and/or males in the group. It is unknown if any individual besides the mother plays a role in parental care for the Arunachal macaque.
As herbivores, Arunachal macaques are themselves predators to the plants they feed on, and may serve as seed dispersers. There are no confirmed non-human predators of Arunachal macaques, although their range overlaps with several large predators that may well predate them, including dholes, Asiatic black bears, and snow leopards.
Arunachal macaques are listed as Endangered on the International Union for Conservation of Nature’s Red List of Threatened Species (IUCN, 2015). Their current population size is estimated to be less than 250 mature individuals with a declining population trend. Between 2004 and 2005, during the initial expeditions leading to the formal description of the species, more than 550 individuals were observed, indicating that the population has likely decreased by more than half since 2005.
The traits that have led to the survival of Arunachal macaques for millennia are unfortunately some of the same ones threatening them in the 21st century. While boldness and risk-taking may have been rewarded by evolution in a resource-scarce environment, these traits have given Arunachal macaques their infamous label as crop raiders in an environment dominated by humans. They are known for their highly destructive raids on crops such as wheat, millet, maize, barley, and fruit, as well as raiding kitchens, granaries, and garbage dumps. This leads to intense conflict with the humans they share habitat with, and Arunachal macaques are often hunted in retribution for their crop raiding.
In one study, people in more than half of 64 surveyed villages reported Arunachal macaques as the most common cause of crop loss. In five of the surveyed villages, 87–100% of villagers reported high levels of conflict with the species. A preliminary analysis estimated the financial losses to be between $70 and $100 per family per year. In two villages, more than 90% of people surveyed acknowledged the occurrence of retaliatory killing of Arunachal macaques.
Besides retaliatory killings, Arunacal macaques face other threats. Hunting is a very widespread practice throughout Arunachal Pradesh, resulting in “empty forest syndrome” in some areas, where the forests remain intact while the wildlife populations are decimated by hunting. However, because Buddhism, which prohibits the hunting of primates, is so common in the area, the macaques are often spared the worst of hunting for food. They are still occasionally hunted for use in traditional medicine, and they are sometimes collected for the pet trade.
This species is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES). It is not known to occur in any protected areas, although it is suspected, but unconfirmed, that there is a population in Mouling National Park.
A number of efforts have been proposed to help reduce Arunachal macaque’s negative impact on crops, including adding crop buffers, deterrents such as water guns or loud noises that scare but do not harm the monkeys, and crop compensation or insurance programs, which would reduce the negative financial impact of the macaques on nearby villages, and thus decrease the likelihood of retaliatory killings. In 2018, India’s Ministry of Environment, Forest, and Climate Change increased compensation for damage to crops or property by wildlife in an effort to reduce human-wildlife conflict, protecting both people and animals. While a step in the right direction, Arunachal macaques will need significant action to prevent their extinction, so soon after their initial discovery by primatologists.
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- Mendiratta, U., A. Kumar, C. Mishra, A. Sinha. 2009. Winter ecology of the Arunachal macaque Macaca munzala in Pangchen Valley, western Arunachal Pradesh, northeastern India. American Journal of Primatology, 71(11):939-47.
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- Sinha, A. and S. Radhakrishna. 2010. Dr. Jekyll & Mr. Hyde: The Strange Case of Human-Macaque Interactions in India. Current Conservation, 4(4):39-40.
- Sinha, A., D. Chakraborty, A. Datta, et al. 2012. The Arunachal Macaque in Mammals of South Asia, Volume One (pp. 198-210). Hyderabad, India: Universities Press.
Written by K. Clare Quinlan, December 2019