GORONTALO MACAQUE

Macaca nigrescens

Geographic Distribution and Habitat
The Gorontalo macaque (Macaca nigrescens), also known as Dumoga-bone or Temminck’s macaque, is one of seven macaque species endemic to the Indonesian island of Sulawesi. They specifically inhabit the middle portion of the island’s northern peninsula, between the Bolango River in the west and the Onggak Dumoga River in the east. Their range overlaps significantly with much of the Indonesian province known as Gorontalo, from which they get their name.

Gorontalo macaques make good use of Sulawesi’s lowland and montane tropical rainforest. They prefer primary forest, but also make occasional use of nearby secondary habitats, such as bamboo forests and piper woods.

TAXONOMY IN TRANSITION

Originally considered a subspecies of the crested black macaque (Macaca nigra), scientists concluded in 2001—following half a century of debate and taxonomic revision—that the Gorontalo macaque is a distinct species. There is evidence, however, that Gorontalo macaques hybridize with crested black macaques on the western slopes of Mount Padang, and with Heck’s macaques (Macaca hecki) on the eastern banks of the Bolango River, where the species’ ranges respectively overlap.

Gorontalo macaque range, IUCN 2020

Size, Weight, and Lifespan
Male and female Gorontalo macaques are roughly the same size on average, with males tending to be slightly larger. Based on museum specimens, the average male weighs approximately 13 pounds (5.8 kg) and has a head and body length of 23 inches (60 cm); a female weighs in at 12 pounds (5.5 kg) and measures 19.5 inches (50 cm) from head to toe.

Typical of Sulawesi macaques, Gorontalo macaques sport very short tails. On average, males appear to have only very slightly longer ones than females: 1 inch (2.6 cm) versus 0.75 inch (1.9 cm), respectively.

Very little is currently known about the life history of Gorontalo macaques, including how long they live in the wild. Based on what we know of other Sulawesi species, they probably live somewhere between 20 and 30 years.

Appearance
Gorontalo macaques look very similar to crested black macaques who live just east of them on the northernmost part of Sulawesi Island’s northernmost peninsula. Both species sport dark fur coats and are approximately the same size and build. Hybrids of these species are even believed to exist in the regions where their ranges overlap. 

Their differences are enough, however, that researchers now consider them separate species. Some of their differences are more obvious than others. For instance, Gorontalo macaques do not have the notable black crest that gives their crested cousin’s the distinguished punk-rock look for which they are notorious. Instead, Gorontalo macaques’ hair lays flat. The two species also sport differently colored buttocks. Crested black macaques’ behinds are a muted pink color, making them stand out prominently against their black fur. The behinds of Gorontalo macaques’ are less defined due to their darker, browner hue.

Diet
Gorontalo macaques mostly eat fruits but are also known to munch on young leaves and specific parts of certain plants. Though overwhelmingly herbivorous, roughly ten percent of their diet also includes protein-rich insects.

Many species of macaques are described as “opportunistic” feeders, meaning that they are not opposed to trying anything seemingly edible that comes their way. Though much research remains to be done concerning Gorontalo macaques, they too likely live, to some extent, by this philosophy.

Behavior and Lifestyle
Macaques are known for being some of the most adaptable nonhuman primates on the planet. Twenty-three species are scattered across the Old World, surviving in a diverse set of environments—including busy cities! Many are semi-terrestrial, meaning they spend some of their time in trees and some on the ground. What little research has been conducted on them so far suggests that Gorontalo macaques are significantly more arboreal than any of their Sulawesi cousins, spending 96% of their time in trees. However, researchers are unsure if this is a natural behavior or one caused by the invasion of humans into their habitats, which may cause them to take cover wherever they can.

Species of macaques are particularly social and gregarious, and they behave according to strict social hierarchies. Individuals tailor their behaviors based on where they fall in the hierarchy, the nuances of which are different for every species. When a macaque breaks social code, others may lash out at them. For what it’s worth, however, macaques are not often as overtly aggressive as they may seem from the outside. They are known for using complex, though sometimes subtle, strategies to mitigate aggressive conflicts, and adversaries typically reconcile after fights. Crested black macaques—Gorontalo macaques’ closest relatives—are known for being particularly theatrical, and put on dramatic displays. Intimidation through theatrics is an effective way for many primates to prevent conflict from escalating further into violence, thereby benefitting the entire group.

Sulawesi is the largest island in the ecological region known as Wallacea—one of the most biologically diverse places on the planet. The island is home to seven endemic species of macaques alone, of which the Gorontalo macaque is one. For all their similarities to each other and macaques around the world, each of species exhibits a unique and rich set of behaviors that, when considered altogether, testify to the Wallacea region’s propensity for biodiversity.

Unfortunately, Gorontalo macaques are one of the lesser studied of these Sulawesi macaques. They are, therefore, the least understood at this time. Though they probably share many behaviors with their closest relatives, crested black macaques, it is also likely that they, too, display a slew of signature characteristics that merely await researchers’ observations.

What Does It Mean?

Affiliative behaviors:
Social interactions that function to reinforce social bonds with a group or which are of mutual benefit to all animals involved in the interaction.

Arboreal:
Physically adapted to living primarily or exclusively in trees.

Biodiversity: 
​The level of variation of life in an ecosystem, a biome, or the entire planet. Biodiversity is a measure of the health and function of an ecosystem.

Biodiversity hotspot:
A biogeographic region with significant levels of biodiversity that is under threat from humans.

Bushmeat:
Meat from wildlife species that are hunted for human consumption, generally in tropical forests.

Disturbed Habitat:
A temporary change in environmental conditions that causes a pronounced change in an ecosystem.

Dominance hierarchy:
A type of social hierarchy that arises when members of a social group interact, often aggressively, to create a ranking system. In social living groups, member are likely to compete for access to limited resources and mating opportunities. 

Endemic:
Native or restricted to a certain area or country.

Estrus:
A recurring period of sexual receptivity and fertility in many female mammals.

Genetic bottleneck:
When a species’ population is reduced in size (i.e. by a cataclysmic event, habitat fragmentation, etc.) limiting the genetic diversity of the species.

Habitat fragmentation:
The process by which a large, continuous stretch of habitat gets divided into smaller, disjointed patches of habitat.

Hierarchy:
A system of organization in members of a group who are ranked one above the other according to status or authority.

Hybrid:
The offspring of two plants or animals of different species or varieties.

Lowland forest:
An equatorial evergreen rainforest, commonly known as a tropical rainforest, which receives high rainfall (80 in; 2 m) throughout the year.

Multi-male multi-female group/unit (MMU): 
A social group consisting of multiple adult males and multiple adult females.

Primary forest:
Also termed old-growth forest, virgin forest, or primeval forest—a forest that has attained great age without significant disturbance and thereby exhibits unique ecological features and might be classified as a climax community, an ecological community in which populations of plants or animals remain stable and exist in balance with each other and their environment.

Semi-terrestrial:
Living partially, but not wholly, on the ground.

Taxonomy: 
A branch of science that encompasses the description, identification, nomenclature, and classification of organisms.​

Visit the Glossary for more definitions

Daily Life and Group Dynamics 
So far, what we know about the lives of Gorontalo macaques is scant. During the day, they mosey through the forest as a group, keeping their eyes peeled for fruit or other food. Sometimes a smaller group, or an individual, breaks off from the larger one, allowing them to go with a bit more purpose and speed. Up to a third of their day is spent foraging the foods they eat, typically in the form of one of these smaller fission groups. As there is safety in numbers, the macaques typically rejoin with the larger group once they have had their fill, resting together among the trees. In total, more than half their day is spent simply relaxing while they digest their meals. Then, they socialize. Adults groom each other in the shade while little ones play, learning and practicing the skills they will need to become successful Gorontalo macaques surviving in the wild. As daylight starts to wane, the group clambers into the trees where they sleep soundly, protected from predators.

Crested black macaques—being more researched—may help us to round out some of mysteries still surrounding Gorontalo macaques’ daily routines and group dynamics. Crested black macaques live in multi-male/multi-female groups ranging from nine to 28 members that adhere to a male dominance hierarchy. In general, the members of the group are led by a single dominant male, but other males typically take charge of smaller groups when they break off to forage separately.

Though other males are technically vying for the alpha’s spot, male-to-male relationships generally remain quite peaceful. Fights tend to be more theatrical than violent, with minimal—if any—bloodshed. Occasionally, males form coalitions with each other in order to oust the current leader of their group. Once a group’s leader is supplanted, he can never regain his former post. Depending on circumstances, he may remain with his current group and fall peacefully into line or choose to leave and join another group where he will have the chance of moving up the ranks again. Female crested black macaques enjoy the protection of males and are generally peaceful, preventing and resolving their conflicts with grooming and other prosocial gestures.

Though our knowledge of other macaque species can certainly help us to imagine the lives of Gorontalo macaques, only more thorough research can give us a genuine understanding of the unique lives they lead in the wild.

Fun Facts

Originally considered a subspecies of the crested black macaque, researchers dubbed the Gorontalo macaque a distinct species as early as 1969. In 1980, however, further research caused them to backtrack this classification. The two species remained conflated once more until 2001, when further research concluded that, in spite of both genetic and morphological similarities, the Gorontalo macaque should be considered its own separate species.

Communication
Communication is key to living in large social groups in which conflicts require prevention, mitigation, de-escalation, and reconciliation. Being particularly social, as well as hierarchical, macaques have developed many nuanced ways by which they actively communicate with one another. Vocalizations, facial expressions, body postures, and hand gestures are some of the ways that primates communicate with each other. While many similarities exist, such behaviors vary greatly between species—possibly even between groups of the same species! No doubt have Gorontalo macaques, too, evolved these sorts of behaviors. However, the specific ways in which they do so are not well-studied at this time.

Male Gorontalo macaques are known to make loud calls to each other in the early morning and late afternoon. They make these same vocalizations during moments of uncertainty, such as in the presence of a possible threat, and in the aftermath of an intragroup conflict.

The communicative behaviors of other Sulawesi macaque species in general are better recorded and can provide insight into how Gorontalo macaques may communicate with each other.

Male crested black macaques, regardless of their rank, often grab each other’s genitals. Though such a gesture may seem overtly sexual to us humans, for these monkeys it is more equivalent to a friendly handshake—albeit with a slight twist. As male macaques vie for dominance of their group, they must frequently interact with each other, sometimes as adversaries and sometimes as collaborators. By handling each other’s genitals, the macaques do more than just greet each other; they share a moment of vulnerability together. In this way they establish trust, preventing potential future conflicts from escalating beyond control. 

When crested black macaques are feeling playful, they retract their scalp and flatten their ears, inviting those around them to join in a game. When individuals perceive a situation to be stressful, they form their mouths into an “O” shape, then fling back their head, yawning big and wide. Vocalizations like chuckles, grunts, and barks are rich with meaning for crested black macaques, but their meanings are highly dependent on the contexts in which they are used.

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 we cannot know that Gorontalo macaques use these selfsame methods of communications until proper research is conducted, 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, especially when two species’ ranges overlap.

Perhaps the most important takeaway from Sulawesi macaque communication is how so many of their behaviors tend to be affiliative rather than aggressive. Clearly, these macaques have vested interests in keeping the peace.

Reproduction and Family
At this time, the life histories of Gorontalo macaques have not been duly studied in the wild. If they are anything like their crested black cousins, however, males and females are quite promiscuous, mating multiple times and with multiple partners. A male’s mating success, however, is largely affected by his rank in the dominance hierarchy.

Mating can occur at any time of the year. When a female is ready to mate, she enters her estrus cycle. Males know she is fertile when her hind quarters swell and brighten, enticing them to mate.

Once she is pregnant, her gestation period lasts for approximately six months. In the end, she births a single infant who she will nurse for one year before weaning. Her offspring reaches sexual maturity within four to six years, with females normally reaching it before males.

While a female remains with her natal group, a male leaves his. Often, newly matured males form bachelor groups. As a member of such a band, a male has the protection of numbers and the comforts of social contact while he searches for a mixed-sex group he can join, and in which he can begin vying for dominance and eventually—hopefully—mate.

Again, Gorontalo macaques may lead surprisingly different lives than their crested black cousins. We cannot truly know what their lives look like in the wild before thorough research is conducted.

Photo credit: © Entol Afnan/iNaturalist/Creative Commons

Ecological Role
​As fruit eaters that move about the forests, Gorontalo macaques disperse seeds through their feces. More research may shed light on other important roles they play in their ecosystems.

Conservation Status and Threats
The Gorontalo 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.

Sulawesi is 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 in the world—a fact that makes it, and all of its flora and fauna, especially vulnerable to even minute changes. The many primates—including Gorontalo macaques—endemic to the island of Sulawesi are each threatened by the rapid expansion of human settlements that destroy their fragile 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 ecosystem in jeopardy.

Forest fragmentation puts species—particularly primate species—at risk of developing genetic bottlenecks. When genes stop flowing between different groups of animals, the lack of genetic diversity gradually makes offspring more prone to contracting diseases, viruses, and parasites, or may cause them to develop other physiological problems that affect their well-being. As this problem persists generation after generation, animals gradually become less and less viable—less likely to mate and successfully rear another generation. For Gorontalo macaques, who rely more on trees than other Sulawesi macaques, undisturbed and continuous forests are particularly precious.

Even the protected forests in Sulawesi are increasingly threatened by human settlements, including illegal gold mining operations. Due to the unlawful nature of their activities, gold 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 the inevitable waste material, it seeps into the soil and water where it quickly becomes part of the food chain. 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 this practice has mostly gone out of style among large-scale gold mining companies, these small-scale, undercover operations are not affected by the moral backlash of using mercury to extract gold, and so they do it without worrying about potential repercussions to their business.

Bushmeat is another industry that adversely affects the primate residents of Sulawesi. Crested black macaques and Gorontalo macaques are particularly prized by local populations. The macaques are cooked and served at special celebrations, like weddings and Christmas dinners. Originally, locals preferred hunting crested black macaques only. Gorontalo macaques, after all, tend to live in more mountainous regions where it is harder for humans to hunt. But as the numbers of crested black macaques decrease in the wild, pressure mounts on Gorontalo macaque populations, who become a more valued target.

Gorontalo macaques are also known to raid crops, making them occasional targets of local farmers. Besides protecting their crops, farmers may have the added incentive to kill trespassing macaques to sell their meat. Hunting is a serious threat to crested black and Gorontalo macaques. Despite it being illegal, it is still quite common to see their meat displayed at local markets.

A key obstacle for Gorontalo macaque conservation is our lack of knowledge about them. 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.

Conservation Efforts
Gorontalo macaques have been protected under Indonesian law since the 1970s, but enforcement of these laws has been less than consistent. Today, the most viable population of Gorontalo macaques lives in the protected Bogani Nani Wartabone National Park, where the Wildlife Conservation Society—a nongovernmental organization—maintains a strong presence. Unchecked hunting, logging, mining, and farming continue to be a threat to Gorontalo macaques, however—even within the national park. So far, the macaques’ most effective protections seem to be natural: the mountainous terrain where they live is often too difficult for humans to hunt in or clear. But these natural protections will never be enough, and only more reliable intervention programs from government agencies and international organizations can make a difference to conserve Gorontalo macaques in the wild.

Other populations of Gorontalo macaques, if they exist elsewhere, are likely quite small. More surveys are desperately needed to determine exactly where Gorontalo macaques can be found in the wild. In general, conducting more research on Gorontalo macaques is necessary to conserving their populations.

Educating the local human populations about the need for Gorontalo macaque conservation is also direly needed. Increasing awareness alone will not be enough to turn the tide, however. Developing programs that encourage locals’ collaboration in conservation efforts, as well as helping them to transition to more sustainable farming practices or alternative livelihoods, like ecotourism, will likely go much further.

Gorontalo macaques are listed on the Convention on International Trade in Endangered Species (CITES) Appendix II.

References:

  • https://www.iucnredlist.org/species/12568/17948400
  • https://www.iucnredlist.org/species/12556/17950422
  • https://link.springer.com/article/10.1007/s10764-019-00082-1
  • https://link.springer.com/content/pdf/10.1023/A:1026330332061.pdf
  • https://www.nationalgeographic.com/magazine/article/macaques-monkeys-indonesia-endangered-pet-trade
  • https://www.jstage.jst.go.jp/article/psj1985/16/3/16_3_203/_pdf
  • https://www.iucn.org/sites/dev/files/import/downloads/12a_27_06_selamatkan_yaki_eubacteria_article.pdf
  • https://www.researchgate.net/publication/349476576_PRIMATES_OF_SULAWESI_AN_UPDATE_ON_HABITAT_DISTRIBUTION_POPULATION_AND_CONSERVATION

Written by Zachary Lussier, June 2021