Geographic Distribution and Habitat
The stump-tailed macaque, also called the bear macaque, is an Old World monkey native to Cambodia, southwest China, northeast India, Laos, Myanmar, northwest Peninsular Malaysia, Thailand, and Vietnam. In the past, this monkey species was also found in eastern Bangladesh, but it is now believed to be extinct in the region.
The stump-tailed macaque is found in tropical and subtropical evergreen forests. These rainforests are crucial to its survival, as they provide adequate food and nutrition unavailable in other habitats, such as dry forests. Intact, undisturbed primary forest is important for maintaining this species, as research has uncovered that stump-tailed macaques prefer to live in primary forest over secondary, disturbed forest.
Size, Weight, and Lifespan
Male stump-tailed macaques tend to be larger than females, a trait known as sexual dimorphism. Males measure between 20 and 26 in (52-65 cm) tall and weigh between 22 and 27 lb (10-12.2 kg). Females are typically between 19 and 23 in (48-58 cm) and weigh around 16.5-20 lb (7.5-9 kg). Stump-tailed macaques may live up to 30 years, but their lifespan in the wild is often shorter due to stressors such as predation.
True to their name, stump-tailed macaques have a short, hairless tail, measuring only 1.25-2.7 in (3.2-6.9 cm). Adults have long, sandy to dark brown colored hair. Infants are born white and darken with age. Stump-tailed macaques’ faces are hairless and bright pink or red. Over time and with exposure to the sun, the red coloration darkens and may even become black. Males have larger canine teeth than females which are used to establish social dominance. All stump-tailed macaques, as well as other macaque species, have cheek pouches in which they store food.
Stump-tailed macaques are primarily frugivorous—the bulk of their diet is made up of many different kinds of fruits. Additionally, they eat seeds, flowers, frogs, birds, bird eggs, and freshwater crabs, when available. In places where macaques live near humans, the monkeys have been known to raid croplands for farmed foods such as corn, rice, and potatoes.
One of the signs of aging in this species is balding—stump-tailed macaques exhibit hair loss patterns similar to male pattern baldness in humans, although in macaques hair loss is seen among both females and males.
Behavior and Lifestyle
Stump-tailed macaques are semi-terrestrial primates. Their large body size and weight make them clumsy climbers so they spend most of their time on the ground. They forage, travel, rest, and groom on the ground, although they are known to occasionally climb trees in search of delicious fruits and to sleep at night. In general, adult males are found in trees more often than other troop members. They climb up to protect and watch over their groups, alerting them to any potential dangers.
Stump-tailed macaques wake up at dawn and forage throughout the morning. They stop a few hours before midday, when it is hottest, to groom, play, and rest in the shade. In the early evening, they being to forage again until sunset, at which point the troop nestles into a few sleep-trees and sleeps until the sun rises and it’s time to begin the pattern again. Daily ranging distances are between 1.2-1.8 mi (2-3 km).
They live in multi-male, multi-female social groups made up of several monkey families. The total number of individuals in any one group can vary from just a few monkeys to up to 60. Males, upon reaching sexual maturity, leave their family group and social group to join a new group. Females remain within the social groups they were born into for the entirety of their lives.
Stump-tailed macaque groups are built upon dominance hierarchies—some monkeys are higher ranking than others, and have special privileges that others do not. Alpha male status is usually determined in intense fights in which the winner achieves a higher social status than the loser. Higher ranking and alpha males have access to more mates and are typically participants in the vast majority of mating within the group. Alpha males also have the added responsibility of protecting the group and will climb trees to keep a lookout for their troop.
Stump-tailed macaques have various means of communication. In the large expanse of the dense and leafy rainforest, it’s easy to get lost. Therefore, these primates “coo” to each other so that even when another monkey is out of sight, the sound of their coo lets their friends and family know they are nearby. They also greet each other by approaching and cooing. In other situations, such as when two monkeys are making up after a fight or when one monkey is requesting to mate with another, they approach each other and make a grunting sound. Alpha males also make another very important sound: they “roar” to scare away potential predators from their group.
One of the most common visual behaviors among stump-tailed macaques is teeth chattering. A low-ranking monkey often chatters his teeth towards a higher ranking individual. It is believed that this behavior promotes group harmony, as it signifies that everyone within the group knows his or her rightful place within the hierarchy. While visual and gestural communication is still under investigation in stump-tailed macaques, another known, prominent behavior within this species is arm-presentation, during which a low-ranking monkey presents his or her arm to a higher ranking monkey as a sign of submission. The prominence of behaviors that communicate individuals’ role in the group indicates that social rank is a very important part of stump-tailed macaque life.
Stump-tailed macaques do not have one mate; they mate with many individuals in their social groups. Higher-ranking monkeys tend to have more frequent access to mates and both male and female macaques initiate mating behavior. Females may approach a male and present her hindquarters, signaling a desire to mate, or a male may approach, touch, or threaten a female to initiate mating. In a behavior unique to stump-tailed macaques, at the end of mating the male will pull the female on to his lap. Once this reproductive process is complete, the male and female separate and return to their previous activities.
Stump-tailed macaque females typically give birth to their first infant around 5 years of age and have one offspring every two years. Pregnancy gestation length is around 175 days and babies are born year-round. Infants are nursed for the first nine months of their life and are dependent on their mothers for the first year and a half.
While a stump-tailed macaque infant’s mother is her primary caregiver, the infant also receives care from other female macaques (and occasionally males) in the group. These secondary caregivers groom and play with the infants and help keep them safe from harm. Under the watchful eyes of her mother and caregivers, an infant stump-tailed macaque is given the freedom to explore and investigate her environment.
As frugivores, stump-tailed macaques eat fruits and deposit their seeds throughout their habitat. This makes them important seed dispersers within their environment—without these monkeys, forest plant growth and regeneration would be impacted.
The stump-tailed macaque is classified as Vulnerable by the International Union for Conservation of Nature (IUCN, 2015), appearing on the IUCN Red List of Threatened Species. Populations are projected to decline over the next 30 years due to threats such as hunting and habitat loss. As human populations and their demand for land increases, primate habitat is often destroyed, fragmented, or degraded so that the land can be utilized by people. For example, in India, land clearing for agriculture reduces stump-tailed macaque habitat and increases the chances of human-macaque conflict. Increasing interactions with humans leads to increased hunting, as the large-bodied macaques are viewed as a significant and easily attainable source of protein.
Certain regional populations of stump-tailed macaques are more threatened than others and at greater risk of extinction. Stump-tailed macaques living in India are at high risk of local extinction due to hunting and habitat loss, while populations in China, Myanmar, Vietnam, Laos, and Cambodia are declining. Populations in Thailand are more stable.
While conservation challenges to stump-tailed macaques are many, so too are conservation efforts working to ensure this species’ continued existence. Protected areas aimed to preserve macaque habitat provide these monkeys with space safe from human encroachment. Protected areas throughout the macaques’ range, such as Balpakram National Park, Mehao Wildlife Sanctuary, Murlen National Park, and Huay Kha Khaeng Wildlife Sanctuary are all known to provide protection to stump-tailed macaques. The establishment of more protected areas throughout their range would offer further protection.
Stump-tailed macaques are protected under the Convention on International Trade in Endangered Species (CITES) Appendix II, which places strict regulations on the trade of stump-tailed macaques and aims to control the number of these animals that are hunted. They are also under wildlife protection acts in India, Vietnam, Myanmar, and Laos, although macaque hunting and trading continues.
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Written by Kylie Sorenson, October 2018