Geographic Distribution and Habitat
Tonkean macaques, also called Tonkean black macaques, are native to the central portion of island of Sulawesi and nearby Togian Islands in Indonesia. They are found in lowland and hill forests at moderate elevations below 5,000 ft (1500 m). The population density is estimated to be roughly three to five individuals per 0.6 square miles (1 sq km).
Size, Weight, and Lifespan
Tonkean macaques weigh between 19 and 23 lb (8.5–10.5 kg) and are between 20 and 26 in (50–67.5 cm) tall. It is not clear how long they live in the wild, but in captivity some individuals have reached the age of 28.
Males are a little larger than females, though both sexes look athletic with strong thighs and arms. Their bodies are covered in long, woolly black hair, accentuated by patches of white on the backs of their legs and their buttocks, faces, and chins. Their faces appear to be chiseled out of wood, with a strong muzzle carved inward on each side and a protruding eyebrow line that makes their round brown eyes appear small and sunken. The patches of white hair on their cheeks add to the majesty of their faces.
When yawning or displaying, they expose a set of frighteningly long and sharp top canines. They have cheek pouches to carry food around while they forage. Like all primates, they have five digits on their hands and feet; despite the fact that their thumb is shorter than a human’s (in relation to the size of their hands), these monkeys are very dextrous.
What Does It Mean?
Having a diet that consists of fruits.
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Tonkean macaques are predominantly frugivorous, but they also eat leaves, flower stalks, buds, and the occasional invertebrate. Most of the fruit they eat is highly nutritious and picked from various fig tree species.
As their natural habitat diminishes due to land conversion for agriculture, they have proven to be adaptable, resourceful, and able to use all strata of the forest. They also raid crops of maize, vegetables, and cocoa, of which they are extremely fond. The cocoa pulp is lower in fiber, protein, and lipids than wild fruit. It also contains tons of easy-to-digest carbohydrates and has the advantage of being available all year long.
Behavior and Lifestyle
These gregarious macaques live in groups consisting of several adult males and adult females and their offspring (juveniles and infants). These groups typically include twice as many females as males. The group is structured around matriarchs, some higher-ranking than others. The dominance hierarchy between matriarchs establishes the dominance hierarchy of their families within the troop.
Unlike other macaque species for whom nepotism and intolerance are the norm, Tonkean macaques are relatively amiable and do not strictly form relationships on the basis of kinship and hierarchy. Members of the group can therefore freely interact with other troop members, irrespective of rank or age. Juveniles, for instance, don’t avoid adult males and establish contact without fearing punishment—even if an adult male is otherwise engaged with a female.
Conflicts arise occasionally. When they do, the threatened individual—male or female—retaliates right away, regardless of the aggressor’s rank or gender. In fact, members of the group often express their grievances toward the highest-ranking male. This does not mean, however, that hierarchies can be toppled easily. In fact, they remain relatively stable for many years.
Because relationship boundaries are more relaxed than in rhesus or Japanese macaque societies, for instance, conflicts never last very long. A mediator usually intervenes between two opponents before things get out of hand. The mediator uses lip-smacks, play, mounting, or clasps to deescalate the situation. Before long, the opponents relax and engage in social grooming. There again, unlike other macaque species, Tonkean macaques are more liberal and all individuals in the group, no matter their kinship, rank, or gender, are free to groom anyone they like.
The same easy-going attitude does not extend to neighboring groups, with whom they can be quite aggressive.
Daily Life and Group Dynamics
The day of a Tonkean macaque is spent traveling, foraging, socializing, and sleeping. Of these activities, resting is what they do most of, both in the wild and in captivity. They like to sunbathe when the temperature is low and stay in the shade in the heat of summer.
They travel together to feeding sites during the day. The group maintains cohesiveness with contact calls, so they know where each individual is at any point in time. They never select food randomly; they prefer items that are easy to digest and provide lots of energy. The size of the group is strongly related to the amount and type of food available—and so is the time they spend traveling and foraging. They spend more time in the trees than they do on the ground during the fruiting and budding season. Conversely, they spend more time on the ground looking for seeds and insects when fruit is less abundant.
Recent studies focusing on the adaptability of these macaques to territory loss due to human activity have shown that they travel shorter distances and spend more time resting and foraging when they live in disturbed areas.
Although no detailed information was found on the subject, it is reasonable to assume that, like other macaques, they retire together at night and build nests. They might also huddle together on a branch for protection against predators.
Tonkean macaques are quite dextrous and creative. A couple of individuals in captivity were observed creating tools out of plant stems. Several studies indicate that they quickly understand how to use new objects and manipulate them. They even seem to collaborate in certain situations to get food rewards—for example, two monkeys simultaneously lift heavy stones to remove food items underneath.
There are seven taxa of primates native to the island of Sulawesi in Indonesia. All derive from one single ancestor and share several characteristics.
Some experiments were conducted to test the theory of mind in Tonkean macaques. The macaques in the study showed that they were perfectly able to distinguish between an experimenter who was unable to give them food items and an experimenter who was unwilling or one who was distracted. Their behavior toward the human experimenter was different based on their understanding of the experimenter’s willingness, unwillingness, or inability to hand out food.
A female Tonkean macaque residing at Parco Faunistico di Piana dell’Abatino, Italy, was observed carrying her dead infant for 25 days. For some unexplained reasons, the body mummified and retained the appearance of an infant for a very long time. Dr. De Marco, who reported the behavior in a paper she and her team wrote, concluded that because the mummification preserved the shape of the infant, the mother’s maternal instincts did not turn off. The young, inexperienced mother continued to groom and lick it, until she finally ate the corpse. No such behavior had ever been reported before.
Tonkean macaques use body posture, facial expressions, and vocalizations to communicate and coordinate travel.
Group movements, for example, are decided collectively through “notifying behavior.” While the group is resting, some individuals may propose a new destination. They do so by moving a few feet away from the group and looking back to see who is willing to follow them in the direction they’re indicating. A few monkeys will join them and wait. It is not unusual for other individuals to indicate they might prefer to go somewhere else. A few monkeys may then decide to join them and wait. When all the group members are ready to go, they decide which direction to go by selecting the “notifying” group with the most individuals, but not necessarily one that includes relatives or higher-ranking macaques.
Tonkean macaques use different vocalizations for different situations. Affiliation calls draw attention to monkeys engaged in “affiliative behavior,” that is, social interactions that function to reinforce social bonds or which are of mutual benefit to all animals involved in the interaction. Twits and cackles are uttered by macaques witnessing a conflict. Alarm calls indicate that a predator is nearby and differ based on the type of predator. Loud calls can be heard when individuals are separated from their group or when a dominant male is tense. The calls are structured in phrases, which are utterances that are repeated between two and fourteen times.
Biting is rare; these monkeys much prefer friendly displays such as lip-smacking, grunts, and clasps. They also often use what is referred to as the “silent bared-teeth” display. Unlike in other species, this display is not submissive. Rather, it is indicative of peaceful intentions and reassurance.
Reproduction and Family
Females become sexually mature at about three years of age and remain in their natal groups. Males reach puberty between the ages of four and five, at which point they emigrate from their natal group.
When they are ready to mate, females exhibit a brightly colored genital swelling and attract mates with a special call. Although they can reproduce all year long, members of the same group do not go into estrus simultaneously. This gives the dominant male the opportunity to form consortships over several days and father most of the offspring. Impregnating most of the females in the group is no easy task, especially when he must protect them from interlopers.
Females give birth to one offspring after a gestation period of 173 days. Babies are dependent on their mothers’ milk for their first year of life and learn how to forage by watching them. Mothers are emotionally attached to their babies and—if the baby dies unexpectedly—may carry a lifeless infant for several days.
Juveniles learn how to socialize through play. They often play-fight with one or several other juveniles and seem to take a lot of pleasure in it, while perfecting the skills that will allow them to survive. Like other macaques, both attackers and defenders almost always aim to bite at the neck, shoulder, and upper arm of their opponents. When play-fighting with one individual, the defender always rotates his or her body to remain face-to-face with the opponent and occasionally delivers a retaliatory bite. When three individuals are playing, the third one usually throws himself on top of the other two and grabs whatever body part he or she can. Sometimes a fourth individual jumps in, and so forth, until many juveniles pile up on top of each other. Group play-fights are more common in Tonkean macaques and last longer than in other macaque species.
Tonkean macaques are seed dispersers and play an important role in the preservation and proliferation of multiple tree and plant species.
Conservation Status and Threats
The Tonkean macaque is classified as Vulnerable (IUCN, 2015) by the International Union for Conservation of Nature , appearing on the IUCN’s Red List of Threatened Species. With land conversion for agriculture, the Tonkean macaques’ natural habitat has been rapidly disappearing—especially since the 1980s when cacao plantations became a steady source of cash for farmers. Because Tonkean macaques raid crops, they are often trapped and killed in retaliation. Although they are able to adapt in degraded forest, their population is declining.
The greatest threat to the species is large-scale conversion of forest for commercial logging and the development of cash crop plantations, such as oil palm and cacao. A key concern is that much of Sulawesi’s remaining forest is montane forest and it is not yet certain whether forest above 6,600 feet (2,000 m) provides habitat that can sustain them year round.
This species is hunted for food in some areas. There is also evidence of hunting pressure on macaques in Central Sulawesi for local consumption and for bushmeat markets in Manado, North Sulawesi.
Tonkean Macaques are often poisoned and trapped as crop pests (or to raise as pets) in many areas. Pet ownership is linked to bidirectional disease transmission between macaques and people. Human-macaque folklore in the Lindu highlands serves to protect local macaques from retaliation by farmers due to crop raiding. It remains to be known, however, at what threshold crop losses will no longer be tolerated and social taboos, and the conservation outcomes they afford, are abandoned.
Their natural predators are large cats, large reptiles, and humans.
In order to protect cacao plantations from crop raiding, local farmers are encouraged to create buffer corridors with plants and trees that Tokean macaques like to eat, such as figs. The other great alternative is sugar palm. The macaques like it and it is available all year long. Humans can collect its sap without killing the tree and can also use the hair fibers to build household items.
Although they treat the macaques as pests, the people of Sulawesi are generally sympathetic to these monkeys. Village elders in and around Lore Lindu National Park believe that humans and monkeys are related because they share many similarities; as such, monkeys should be treated with respect. Sulawesi folktales even talk about a forest fire and how some people burnt and became monkeys. For this reason, conservationists believe that, combined with education on environmental issues, local culture and traditions can play an important role in the protection of not only Tonkean macaques but all local biodiversity.
- Current Primatology, Vol. 2: Social Development, Learning and Behavior, Roeder J.J., Thierry B., Anderson J.R. & Herrenschmidt N. (eds.), Université Louis Pasteur, Strasbourg, pp. 103-117, 1994. // Tonkean macaque behavior from the perspective of the evolution of Sulawesi macaques – B. Thierry, J.R. Anderson, C. Demaria, C. Desportes, O. Petit.
- International Journal of Primatology (2011) 32-708-720 / DOI 10.1007/s10764-011-9496-9 – Interactions Between Third Parties and Censorship Partners in Tonkean Macaques (Macaca tonkeana) – Arianna De Marco, Roberto Cozzolino, Francesco Dessì-Fulgheri, Bernard Thierry.
- Current Zoology 57 (1): 8-17, 2011 – Land use in semi-free ranging Tonkean macaques Macaca tonkeana depends on environmental conditions: A geographical information system approach – Cédric Sueur, Paul Salze, Christiane Weber, Odile Petit.
- UCLA – International Journal of Comparative Psychology – Targets and Tactics of Play Fighting: Competitive versus Cooperative Styles of Play in Japanese and Tonkean Macaques – Reinhart Christine, Ellis Vivien, Thierry Bernard – ISSN 0889-3667 (2010).
- Nutritional content explains the attractiveness of cacao to crop raiding Tonkean macaques – Erin P. Riley, Barbara Tolbert, Wartika R.Farida
- The importance of human-macaque folklore for the conservation in Lore Lindu National Park, Sulawesi, Indonesia. Erin P. Riley.
- Where Next? Group Coordination and Collective Decision Making by Primates – Andrew J. King, Cédric Sueur – International Journal of Primatology (2011) 32:1245-1267 / DOI 10.1007/s 10764-011-9526-7
- “Unwilling” versus “unable”: Tonkean macaques’ understanding of human goal-directed actions – Charlotte Canteloup and Hélène Meunier
- Youtube – “Singes démocrates” – Cédric Sueur – Centre primatologique de Strasbourg, France.
- The Loud Call of the Sulawesi Tonkean macaque. Erin P. Riley
- Prolonged transport and cannibalism of mummified infant remains by a Tonkean macaque mother – Arianna De Marco, Roberto Cozzolino, Bernard Thierry – Primates, January 2018 – vol. 59, issue 1, pp 55-59.
Written by Sylvie Abrams, April 2019. Conservation status updated December 2020.