Geographic Distribution and Habitat
Having learned to thrive in a wide range of habitats, the bonnet macaque (macaca radiata) is highly visible throughout India’s southern peninsula. Comprising two subspecies, the more common dark-bellied bonnet macaque, macaca radiata radiata, is found in the peninsula’s evergreen and deciduous forests, on dry prairies, and in urban spaces, such as tourist-drenched temples and on the outskirts of villages. The less abundant subspecies, the pale bellied bonnet macaque, macaca radiata diluta, keeps to the forests in southeastern coastal India, in the Western Ghats mountain range, and northeastward to the city of Pondicherry.
The scrappy bonnet macaque’s ability to live commensal with humans presents perhaps its greatest vulnerability: although the species appears abundant and at ease among humans, recent studies suggest its numbers may be declining faster than previously thought and conflicts with humans further plague this resourceful Asian monkey.
Size, Weight, and Lifespan
Bonnet macaques share some common traits with the approximately 22 other types of macaque species recognized today: within species, arms and legs are about the same length and sexual dimorphism is present, with males growing larger than females. A bonnet macaque is smaller than many other macaque cousins, weighing, on average, about 8.5lbs (3.9kg) for females and 14lbs (6.7kg) for males, with average lengths of 14in (35cm) to 24in (60cm), for females and males respectively. The tail measures two-thirds the length of the body.
In captivity, bonnet macaques may live up to 35 years, but not so in the wild. Disease, encounters with predators, and conflicts with humans typically cut a bonnet macaque’s lifespan to 20-25 years (many bonnet macaques are killed as pests to crops or in collisions with vehicles).
Bonnet macaques earn their common name from a singular feature: a cap-like tuft of hair fanning out from the top of the head, so much like a tussock of dry grass. The two subspecies are distinguished by the color of their bellies—macaca radiata radiata bear dark bellies while their macaca radiata diluta counterparts have pale bellies. Both have gray- or golden-brown coats.
Framed by large ears, the wrinkled, hairless face of a bonnet macaque begs attention. In females, the face is pink. Her marble-round eyes stare out at the world from a highly expressive brow. Large teeth may be displayed in aggression or fear.
As is common in Afro-Eurasian monkeys, a bonnet macaque has cheek pouches for storing food and narrow, down-facing nostrils. While her sense of smell appears to be less developed due to her narrow nostrils, a bonnet macaque can rely on her sense of taste to confirm when fruit is ripe and ready for consumption. With eyes that see in color and nimble, sensitive hands, she deftly navigates her world. Scientists have observed juveniles using their tails for support while climbing, even though the tail itself is not prehensile—that is, capable of grasping objects like branches.
The bonnet macaque spends much of his time inhabiting temples and other urban places where he can readily consume human food. Although he prefers fruits and plant materials, he’s an omnivore and will resourcefully rummage for nourishment in nearby houses, food stalls, gardens, and trash piles. Sometimes, tourists will find entertainment in feeding the monkeys, making the foraging work all the easier. Pale-bellied bonnet macaques and other forest-dwelling bonnet macaques eat fruits, soil, insects, and sometimes small invertebrates and reptiles.
Consuming high concentrations of fruits, plant materials, and certainly human foods can upset even the most robust of digestive systems, but the bonnet macaque appears to have a way to alleviate indigestion, nausea, and diarrhea. A study conducted in the Marakkanam Reserve Forest of southern India found that bonnet macaques ate the soils of termite nests, known as termitaria, which are rich in kaolin and smectite. The combination of these materials, when consumed, mimics the mineralogy of eko, an African remedy for stomach ailments, and Kaopectate™, a western anti-diarrheal preparation.
Behavior and Lifestyle
Primatologists classify bonnet macaques as both arboreal and terrestrial—meaning they live in trees and on the ground. As quadrupeds, they walk on all fours and spend a great deal of their daily life on the ground, where they have access to food, whether that be foraged or hand-fed by humans. They navigate the canopy with aplomb, stabilized by their ability to keep three or more limbs in contact with branches at all times.
Humans and bonnet macaques alike have become accustomed to interacting with each other. The dark-bellied bonnet macaque commonly loiters in and around human spaces, including temples and villages, and has been seen resting in ficus trees near to where humans live. Villagers sometimes sell fruit or rice to tourists for the sole purpose of feeding the monkeys.
Another name for the bonnet macaque is zati, a name used infrequently today but commonly used in Britain during the late 1700s. Capped macaque, bonnet monkey, and crown monkey are other terms used to describe the bonnet macaque.
Bonnet macaques live in multi-male, multi-female troops of about 30 individuals, organized in a linear, age-ranked order. It’s interesting to note, however, that this social hierarchy appears to bear less influence over some of the bonnet macaques’ most common behaviors, such as social grooming. Unlike typical allogrooming seen in other species, higher-ranking bonnet macaques have been observed grooming lower-ranking troop members. All troop members participate in this calming and bonding activity.
While a male will move between troops to gain rank, a female will generally stay with the troop into which she was born. Pale-bellied female bonnet macaques, however, are an exception, and have been observed dispersing among groups. As a diurnal species, bonnet macaques are most active during the day. At night or when resting, same-sex bonnet macaques will huddle together, while dominant males will clasp juvenile males close to them. Researcher observations also suggest that adult female mothers tend to huddle together, away from huddles of juveniles, single adult females, and babies.
The alarm call is one of the most important forms of communication for the bonnet macaque. When predators such as pythons or leopards come close, bonnet macaques will emit a high-pitched call that drives the troop into the safety of the canopy. Some studies note that bonnet macaques can also recognize the alarm calls of other primate species with which they coexist, such as Nilgiri langurs (trachypithecus johnii) and northern plains gray langurs (semnopithecus entellus).
For affection and tension relief, bonnet macaques will grin, smack lips, and click tongues. A grimace is a sign of submission or fear. Large males greet each other by embracing, grinning, and gripping each other’s genitals.
One recent study conducted by researchers from the National Institute of Advanced Studies (NIAS) in Bandipur National Park suggests that a bonnet macaque in the wild may also use referential gesturing during social grooming to indicate to where he would like to be groomed (a shoulder or arm, for example)—a communication behavior previously thought to only be found in captive monkeys.
The philopatric female bonnet macaque brings a level of hierarchical stability to her troops; when females remain with their natal group, hierarchy remains relatively unchanged. Males, however, disperse to other troops as they mature, and must compete heavily for status and reproduction.
Competitive fighting among males intensifies during the tense few months during which females are receptive to mating (which peaks in September and October). Unlike other female macaque species, female bonnet macaques do not have sexual swellings, which some researchers believe contributes to the formation of unique bonds between males in this species. It’s also not uncommon, for example, to see male coalitions forming among lower-ranking males in order to overthrow a higher-ranking male.
Females typically bear one offspring each year. A mother keeps her infant very close—often on her back or in her arms—for the first six months to 12 months of life, nursing for a majority of that time. After weaning, the infant remains under the watchful eye of his mother, but the workload is shared, with the whole community taking part in protecting the young. At one-year old, a bonnet macaque is able to fend for himself.
Males also play an important role in the protection and rearing of juveniles and infants. Adult male bonnet macaques will regularly join in play with juveniles, who appear to have the freedom to leap on, kick, cling to, and bite adult males without punishment. Males will keep watch over juvenile males during sleep.
With a diet high in fruit and seeds, forest-dwelling bonnet macaques likely play a role in tree propagation by dispersing seeds throughout the forest floor.
The International Union for Conservation of Nature lists bonnet macaques as Vulnerable (IUCN, 2015), appearing on the IUCN’s Red List of Threatened Species. The species has undergone massive declines over its entire distribution range. It is estimated that the declines are over 30% in the last three generations (36-39 years) due to hunting, persecution, faulty translocations altering group compositions, road expansion, removal of native avenue trees, feeding by humans, and displacement by Rhesus macaques in the northern parts of the range. It is suspected that the declines will continue in the future, but if the threats are not mitigated there might be higher rates of decline necessitating a re-evaluation of the status.
Threats to the bonnet macaque include human intolerance and conflicts. The species is treated as a pest to crops. In urban areas, a bonnet macaque can become aggressive and destructive as he searches for food. Like many of their macaque cousins, bonnet macaques are hunted locally and sold as pets and for research. (In North America, macaques appear to be the most common non-human primate used in biomedical research, but the bonnet macaque is used less frequently than rhesus or cynomolgus macaques).
Known predators, other than humans, include pythons, tigers, leopards, eagles, and feral dogs.
Bonnet macaques are listed as an Appendix II species by CITES (the Convention on International Trade in Endangered Species of Wild Fauna and Flora), which means that although there’s no immediate threat of extinction, close monitoring is warranted. To help protect the bonnet macaque, CITES advocates conservation of its commensal habitat, specifically patches of scrub forests in the hilly terrains where temple-based troops are situated.
A study published in August 2017 by researchers from the University of Mysore and the Salim Ali Centre for Orthinology and Natural History, found that although the bonnet macaque and other commensal species appear abundant, “it is necessary to pay attention to their conservation and management before such species become threatened.” The study, in which the researchers suggest “urgent conservation action is needed,” explored population changes over more than two decades and found that the distributional range of the bonnet macaque is shrinking in the face of rhesus macaque populations encroaching from the north.
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Written by Christine Regan Davi, September 2017. Conservation status updated July 2020.