Geographic Distribution and Habitat
The Heck’s macaque is endemic to Indonesia in the northwestern province of Sulawesi at the base of the northern peninsula. Northern Sulawesi is primarily mountainous with many areas over 3,280 ft (1,000 m) in elevation and multiple active volcanoes. There are highland and lowland rainforests present in the region. Elevations range from sea level to 4,432 ft (1,351 m) with an annual rainfall between 4 and 8 ft (1.5–2.4 m) and fairly constant temperatures ranging from 71 to 94 degrees F (22–34 C).
There is very little data published about the behavior, ecology, social organization, and reproduction of Heck’s macaques.
Size, Weight, and Lifespan
While the exact size, weight, and lifespan of Heck’s macaques is unknown, we can surmise that they are similar to another macaque that also inhabits Sulawesi, the crested black macaque (Macaca nigra).
Crested black macaques are sexually dimorphic, with males almost twice the size of females. Males are about 1.71–1.87 ft (52–57 cm) in length and weigh about 21.8 lbs (9.9 kg), while females range in length from 1.46 to 1.8 ft (44.5–57 cm) and weigh 12.1 lbs (5.5 kg). Males also have enlarged canine teeth that are utilized during aggressive encounters with other males; females generally have smaller canine teeth.
Heck’s macaques are rarely photographed or observed, so it is difficult to provide a complete description of their appearance, though they look quite similar to crested black macaques. (In fact, most pictures of Heck’s macaques actually turn out to be crested black macaques.) They both have small, almond-shaped brown eyes, a silky black pelage, and little vestigial stubs for tails, which actually causes some to misidentify these Old World monkeys as apes instead.
However, there are still some key differences to take note of—mainly, the giveaway spiky black crest on the head of a crested black macaque, which the Heck’s macaque lacks. Heck’s macaques have a wide, protruding browline and narrow faces with sunken cheeks.
Heck’s macaques are frugivorous. They store food in their cheek pouches while foraging and carry the fruits away to savor and enjoy away from the stresses of competitors or predators. Similarly, crested black macaques are also frugivorous and spend 70% of their time feeding on fruit—but they also consume seeds, leaves, flowers, pith, herbs, grass seeds, fungus, bird eggs, birds, and small vertebrates such as lizards and frogs.
Behavior and Lifestyle
Very little is known about the behavior and lifestyle of this species. They are one of the least studied of the Sulawesi macaques. They are diurnal and semi-arboreal and travel quadrupedally through the trees and along forest floors of primary and secondary tropical rainforests.
What Does It Mean?
Of, relating to, or being aggressive or defensive social interaction (such as fighting, fleeing, or submitting) between individuals usually of the same species.
Physically adapted to living primarily or exclusively in trees.
Pockets on the side of the head between the jaw and the cheek that some animals have to store food.
Active during daylight hours.
Having a diet that consists of fruits.
The process by which a large, continuous stretch of habitat gets divided into smaller, disjointed patches of habitat.
Based on a line of descent through the female.
The group into which an animal is born.
Old World monkey:
Monkeys native to Africa and Asia.
The fur, hair, or wool of a mammal.
Using four limbs to move about. This word comes from the Latin meaning “four feet.”
When males and females have different characteristics (size, color, etc.) other than their reproductive organs.
A part of the body that in the course of evolution, has degenerated and become functionless; the last small part that remains of something that once existed.
Visit the Glossary for more definitions
Daily Life and Group Dynamics
Heck’s macaques have a multi-male/multi-female social system with group sizes that include anywhere from approximately ten to twenty individuals. Females will remain with their natal group until the onset of maturity, but males disperse shortly before adolescence. Based upon the matriline, there is a hierarchical system among group members, which makes sense considering the females do not leave their natal groups.
Heck’s macaques utilize a few communication techniques that are both verbal and visual. Scream calls are emitted when approached by another Heck’s macaque from a different group. Fear grimaces reduce aggression in possible agonistic encounters, they retract their lips to display clenched teeth. Staring with an open mouth is a posture that is used as a threat expression and is performed with a stare and open mouth with covered teeth.
Reproduction and Family
Very little is known about the reproduction and family life of Heck’s macaques; essentially, we know that females give birth to a single offspring and that breeding is non-seasonal. So given the lack of literature on the subject, we will again turn toward the Heck’s macaque’s substitute: the crested black macaque, which has a gestation period that lasts a little under six months and results in the birth of a single offspring. Female crested black macaques reach sexual maturity at anywhere from four to six years of age—usually earlier than the males—and, similar to female Heck’s macaques, they remain with their natal group. Young male crested black macaques leave their birth group upon maturity and eventually seek a group of their own.
Due to their fruit-rich diet, it is likely that Heck’s macaques act as seed dispersers throughout their habitat.
Conservation Status and Threats
The International Union for Conservation of Nature’s Red List of Threatened Species lists Heck’s macaques as Vulnerable with a decreasing population trend (IUCN, 2015).
This species is listed as Vulnerable because of their continuing population decline—greater than 30 percent over the next 40 years as estimated by the current rates of habitat conservation and increasing human population densities.
The greatest threat to the Heck’s macaque is loss of habitat, which is becoming more and more fragmented. Uncontrolled and illegal logging has plagued Sulawesi; unfortunately, it will continue to do so unless authorities implement stricter regulations.
They are also captured, poisoned, shot, and persecuted by local farmers who consider them pesky crop raiders.
Heck’s macaques are listed under the Convention on International Trade in Endangered Species (CITES) Appendix II and they inhabit six different protected areas: Dolangan Reserve, Mas Popaya Raja Reserve, Panua Reserve, Panji Binanga Reserve, Pinjam/Tanjung Mantop Reserve, and Tangale Reserve. Of course, it would greatly benefit Heck’s macaques—and the rest of the biodiverse species they cohabitate with—if more of their habitat gained protection.
Additionally, more local education about their conservation status could reduce the less-than-friendly encounters with local farmers and inspire more people to call for better protections of this species.
Written by Rachel Heim, March 2020