Geographic Distribution and Habitat
The booted macaque (Macaca ochreata) lives in the tropical rainforests of Sulawesi, Indonesia. The species’ range extends from the lakes region in the north—where it overlaps with that of the Tonkean macaque (Macaca tonkeana)to the southern edges of the island’s southeastern peninsula.
Further south, on the smaller islands of Muna and Buton, lives a subspecies of the booted macaque known as the Muna-Buton, or Buton, macaque (Macaca ochreata brunnescens), which is isolated from the type species of Sulawesi.
Size, Weight, and Lifespan
A booted macaque’s body mass is determined by his or her gender, with males being noticeably larger than females. Even after puberty, a male can continue to grow in size and in proportion to the amount of food available to him. Males, therefore, tend to vary in size, ranging from 20–26 pounds (9–12 kg). Adult females all weigh in at roughly the same size, around 11–15 pounds (5–7 kg).
The Muna-Buton subspecies is slightly smaller on average than the type species native to Sulawesi, but the difference is not altogether significant. Head breadth is the only noteworthy statistical distinction, with the Muna-Buton exhibiting a narrower head than its Sulawesi counterpart.
The typical lifespan of a booted macaque in the wild is not currently known.
Female booted macaques have dark, rounded faces with inset, forward-facing eyes. A mane of light-colored brownish gray fur fans outward, hiding her ears. The top of her mane is black. Her slim torso is also covered in black fur that ends at her rump and the beginning of her limbs. These sections fade to a color similar to, but lighter in hue than, that found in her mane. The fur around her hands and feet fades back to a darker hue that is a bit brown in color.
Males exhibit the same basic patterning as females, but are bigger in size. Specific coloration seems to vary more by individual than sex. Other than size, a key distinction between males and females are the males’ much larger upper canine teeth.
Muna-Buton macaques also have boot-like lighter patchers of fur around their limbs and vest-like darker patches covering their torsos, with possible differences in coloration. On average, individuals of this subspecies are a bit smaller than their Sulawesi counterparts, most notably in the width of their heads.
Booted macaques are frugivorous, eating mostly fruit. However, in the event that fruit becomes scarce, individuals have also been known to eat the immature leaves of certain plants, the stalks of newly flowering plants, and even the occasional arthropod.
The increasing existence of farms and plantations in the regions where they live has led booted macaques to develop a special fondness for cultivated crops as well.
What Does It Mean?
Social interactions that function to reinforce social bonds with a group or which are of mutual benefit to all animals involved in the interaction.
An invertebrate animal (one with no spine) having an external skeleton, a segmented body, and jointed appendages. Includes insects, spiders, crustaceans, and myriapods.
The branch of biology that deals with the relations of organisms to one another and to their physical surroundings.
Native or restricted to a certain area or country.
Having a diet that consists of fruits.
A system of organization in members of a group who are ranked one above the other according to status or authority.
Familial relationships that can be traced through a female.
A subtle difference or distinction in expression, meaning, response, etc.
Old World monkey:
Monkeys native to Africa and Asia.
Living partially, but not wholly, on the ground.
Distinct difference in size or appearance between the sexes of an animal in addition to difference between the reproductive organs themselves.
A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
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Behavior and Lifestyle
The lives that booted macaques lead in the wild, and the behaviors they exhibit are not well-studied at this time. However, what we know of macaque species in general, especially of those that are also native to Sulawesi, such as the Tonkean macaque, can give us some insight into how the two subspecies of booted macaques might live and behave.
Macaques are known for being the most adaptable nonhuman primate on the planet. Twenty-three species are scattered across the Old World, surviving in a diverse set of environments, including busy cities! Most are arboreal, but some, including the booted macaque, are semi-terrestrial, meaning they spend some of their time on the ground.
Species of macaques are particularly gregarious but also behave according to a strict social hierarchy. Individuals tailor their behavior based on where they fall in the hierarchy. When someone breaks social code, others may lash out at them. For what it’s worth, however, macaques are not as overtly aggressive as they may seem from the outside. They are known for using complex, though sometimes subtle, strategies to mitigate aggressive conflicts; adversaries typically reconcile after fights.
Tonkean macaques are known for being an especially amiable species. The fact that groups of Tonkean and booted macaques are known to occasionally intermingle and socialize with one another could suggest that they have similar demeanors and social protocols.
Daily Life and Group Dynamics
Though little research has been completed on the daily lives of booted macaques, it is safe to assume that their days probably look quite similar to those of other macaque species found in Sulawesi. Tonkean macaques, who are better-studied, sometimes socialize with groups of booted macaques, suggesting they might have similar routines.
Tonkean macaques live in groups of 12–30 members that consist of multiple adult males and females and their offspring. Typically there are twice as many females in a group as there are males. Common to macaque species, their groups are matrilineal and hierarchical, meaning that one’s social status is passed down through the mother. Tonkean macaques are a particularly amiable variety of macaque, however. Unlike in other species, group members are free to associate with anyone regardless of their status, making social mobility more possible.
The group spends its day traveling between feeding sites where the macaques forage together. When they have had their fill, the group settles down to rest and socialize. Adults groom each other while young ones play. In cool weather, Tonkean macaques are known to enjoy sunbathing. Later, the group might move on to another feeding site, or else settle down to sleep for the night.
In 2016, a group of booted macaques were successfully released back into the wild by the Southeast Sulawesi Conservation of National Resources Agency (BKSDA) after they had moved into the city of Kendari, becoming trapped in the city center.
The Muna-Buton macaque, currently considered a subspecies of the booted macaque, may be its own species altogether.
Booted macaques frequently hybridize with Tonkean macaques where the two species’ ranges overlap.
Groups of Muna-Buton macaques may also live on the islet of Palau Labuan Blanda.
Vocalizations, facial expressions, body postures, and other types of movement are ways that primates communicate with others. Communication is key to living in large social groups in which conflicts arise that require prevention, mitigation, or de-escalation. Being particularly social, as well as hierarchical, macaques have developed many nuanced ways by which they actively communicate with one another. While many similarities exist, such behaviors may vary between species—possibly even between groups of the same species! No doubt have booted macaques, too, evolved these sorts of behaviors. However, the specific ways in which they do so are not well-studied.
The communicative behaviors of other Sulawesi macaque species in general are better recorded and can provide insight into how booted macaques might communicate. Altogether, the social repertoire of Sulawesi macaques is known to be especially complex compared to other macaque species, consisting of almost 150 vocalizations, facial expressions, body postures, and other significant movements or behaviors. While only a few of these have been observed in booted macaques, comparisons of several other better-studied Sulawesi species suggests that all Sulawesi species are likely to have repertoires that are more similar than they are different.
Where their ranges overlap, groups of booted macaques are known to mingle with groups of Tonkean macaques. Tonkean macaques are one of the better-studied species of Sulawesi macaques and are known to make a wide range of vocalizations, which individuals use to consciously communicate their inner emotional states and share other important information. For instance, a mother interacting lovingly with her infant might makes a series of loud and expressive calls that serve to reinforce and nurture their bond. During episodes of aggression, such as intense staring or chasing, a male might form an “O” with his lips and let out a loud bark-like sound in an attempt to intimidate his opponent.
A Tonkean macaque also uses behavior that notifies others of her wants or needs. After a rest, a macaque might get up from her spot and move away from the group in the direction of the foraging spot she hopes to visit next. She looks back to see who will follow her. Those that gather around her communicate that they also wish to go to that foraging spot next. But another in the group might suggest a different direction, and others join his party. In the end, the group with the most individuals “wins,” and they set off in the respective direction. Researchers have determined that the macaques are not influenced by members of their immediate family, suggesting that this process is, in fact, as democratic as it seems.
A consistent facial expression used by all macaque species, including the booted macaque, is what researchers dub the “silent bared teeth” expression. Theorized by some to be a sort of evolutionary prototype of the human smile, a macaque who bares his teeth is one who comes in peace. By announcing that he means others no harm, he assuages any potential tensions and creates opportunity for more intimate interactions to take place. The expression is also in popular use among macaque infants, who use it to signal when they are playing.
Perhaps the most important take-away from Sulawesi macaque social repertoire is how so many behaviors are affiliative and not aggressive. Clearly, these macaques have vested interests in keeping the peace.
Reproduction and Family
Though booted macaques are not well-studied, enough is known about Tonkean and other Sulawesi macaques to provide some possible insights into how they reproduce and what their familial relationships look like.
The females of several Sulawesi macaques, including the Tonkean, regularly develop brightly colored swellings around their genitals. When such a swelling appears on a female, it signals that she is ready to mate. Mating can occur year-round, and rarely do multiple females in a group develop swellings simultaneously. Typically, only the dominant male has the right to mate; however, other males may be successful in secret. To prevent such covert trysts from happening, the dominant male may guard a female who is beginning to show signs of swelling.
Once impregnated, it takes approximately 170 days before a female gives birth. She produces a single infant who is completely dependent on her. For the first year of his life, he clings to her fur, hardly ever leaving her side. As she weans him, he begins to practice the skills that will eventually turn him into a competent and adaptable adult macaque. Climbing and leaping between trees are skills every little macaque must practice on their own—they are not instinctual. Likewise, he learns the art of foraging by observing and imitating what his mother does. When he gets a little older, he forms relationships with other juveniles. Playing together, the young macaques begin to learn the finer elements of macaque society, honing their social and communication skills.
The ecological role of the booted macaque has not been studied. However, if that of the Tonkean macaque is any indication, then booted macaques likely act as seed dispersers for several species of trees and other endemic plants.
Conservation Status and Threats
The booted macaque is listed as Vulnerable by the International Union for Conservation of Nature (IUCN, 2015) appearing on the IUCN’s Red List of Threatened Species.
Like so many other primates, booted macaques are threatened by rapid expansion of human settlements into their habitats. Infrastructural and other development projects fragment or destroy the forests they rely on for food and space, putting the well-being of the entire eco-system in jeopardy. The large island of Sulawesi, and the smaller islands of Muna and Buton that booted macaques call their home, are part of what is known as the Wallacea region. A long history of unique geographical factors has made this region into one of the most endemically rich areas of the world: a fact that makes it, and all of its flora and fauna, especially vulnerable to changes.
Even the protected forests in Sulawesi are increasingly threatened by illegal gold miners. Due to the unlawful nature of their activities, these miners frequently use mercury in their extraction of gold. When they heat the mercury during this process, it escapes as vapor into the atmosphere; when they do not properly dispose of waste material, it seeps into the soil and water where it quickly becomes part of the foodchain. Mercury is known for its negative effects on biology; inhaling or ingesting this heavy metal can wreak havoc on one’s nervous, digestive, and immune systems and does irreparable damage to the lungs and kidneys. While it has mostly gone out of style among large-scale gold mining companies, these small-scale, undercover operations are not effected by the moral backlash of using mercury to extract gold, and so they do it without worrying about potential repercussions to their business.
In this area of the world, cacao, palm oil, and cotton are popular, valuable crops to grow; large swathes of forest are increasingly cleared in order to grow them. Other, more edible crops of fruits and vegetables are also grown. This trend not only brings about the transformation of more habitat, it has also ignited tensions between humans and macaques who raid these crops. Though the religious and traditional views of nonhuman creatures held by the local peoples typically keep this conflict in check, there is fear among conservationists that more and more farmers may start hunting or poisoning crop-raiding macaques if concerted, less hostile efforts are not soon taken that adequately alleviate these tensions.
A key obstacle for booted macaque conservation is a lack of overall research. Knowing the behavior and ecology of a species gives conservationists significant insight into how they can best help it to thrive in the wild. Without this information, efforts ultimately lack the nuance that bona fide success is likely to require. The fact that booted macaque populations are becoming increasingly reliant on farmed crops complicates the matter of researching them, however. These types of crops are not only easier for the macaques to forage, they also have a higher nutritional value than anything offered by their natural habitat. In this semi-domesticated situation, groups of booted macaques find themselves with more time to rest and socialize than they would otherwise have in complete wilderness. This influence, in turn, makes booted macaques’ natural behaviors increasingly difficult for researchers to properly appraise.
Booted macaques live in a number of protected areas in Sulawesi, including the Faruhumpenai Nature Reserve, Rawa Aopa National Park, the Tanjung Peropa Game Reserve. Populations of the Muna-Buton subspecies, on the southeastern islands of Muna and Buton, are protected in the Buton Lambusango Nature Reserve and the Napabalano Nature Reserve.
Direct efforts to conserve booted macaques currently focus on easing tensions between farmers and the macaques who increasingly raid their crops. Conservationists fear that if nothing is done to deescalate this situation, farmers may choose to poison or hunt them as pests. Efforts to plant buffer zones along plantation edges, composed of trees of no interest to macaques, appear to decrease the rates at which macaques raid crops. However, it is not yet clear how effective these buffers really are, or if it will be enough to keep the the conflict from escalating.
This species is listed under the Convention on International Trade in Endangered Species (CITES) Appendix II.
Written by Zachary Lussier, August 2020