PAGAI ISLAND MACAQUE
Geographic Distribution and Habitat
The Pagai Island macaque is an arboreal monkey that lives in Indonesia. They live in primary and secondary forests in tropical rainforest environments. They live high in the canopy, foraging around 79–118 feet (24–36 m) in the trees. They have been found to sleep as high as 148 feet (45 m) in the canopy! As the name may suggest, the Pagai Island macaque, indeed, lives on Pagai Island, which is a part of the Mentawai Islands off the west coast of Indonesia. There are four islands associated with the Mentawai Islands, and the Pagai Island macaque can be found on three of them (North Pagai, South Pagai, and Sipora). Their habitat is extremely wet, with the average rainfall being around 157 inches (400 cm) per year. They are sometimes found in riverside areas and coastal swamp forests. They can also be found living and foraging in coconut groves. The Pagai Island macaque shares its habitat with three other primate species, the Mentawai gibbon, pig-tailed langur, and Mentawai langur. The size of this monkey’s home range is currently unknown.
The Pagai macaque has had a rollercoaster journey through taxonomic labeling. Until recently, they were thought to be the same as Siberut macaques, Macaca siberu. However, after genomic testing and further investigation of their morphology, they were classified as two separate species. Earlier than that, the Pagai Island macaque was considered to be a subspecies of the southern pig-tailed macaque, Macaca nemestrina.
Size, Weight, and Lifespan
Generally, the Pagai Island macaque is sexually dimorphic, meaning the males are larger than the females. The males’ weight will range from 13 to 19 pounds (6–9 kg), and the females weigh somewhere between 9 and 13 pounds (4.5–6 kg). The males are around 18 to 22 inches in length (45–55 cm), and females 16 to 18 inches (40–45 cm) in length. There is more research needed on the lifespan of these monkeys; however, most macaque species live around 25 to 30 years in the wild.
The Pagai Island macaque has a chocolate-brown color on their back. Covering their shoulders, arms, and bellies is a creamy beige to chestnut color. Their tails are primarily hairless, with the exception of the base, where a small tuft of hair can be found. They are hairless on their face and have dark skin and dark eyes. Like most macaques, this monkey has cheek pouches that they use to store food.
The Pagai Island macaque is primarily frugivorous, meaning their diet consists heavily of fruits. They mostly eat figs and coconuts, which are abundant on Pagai island, as well as other fruits they may find. Although all of the Pagai Island macaques may eat coconuts, only the males are physically able to open them. Their close relatives, Siberut macaques, dine on breadfruit, fishtail palm, and jointfir, which suggests that Pagai Island macaques may also enjoy these fruits as well. As mentioned previously, this monkey has cheek pouches that they use to carry food. Mothers may use them to carry food for their infants, or simply for a late-night snack. They have been known to raid local gardens and coconut groves, which results in local people increasingly viewing them as nuisances.
Behavior and Lifestyle
Pagai Island macaques spend much of their day foraging and can sometimes be seen co-foraging with other primate species, such as Mentawai langurs and pig-tailed langurs. During foraging, they will go to lower levels of the canopy or even the ground sometimes. They can be heard early in the morning vocalizing to their neighbors, notifying other forest dwellers of their presence. These monkeys’ natural predators are the crested serpent eagle and reticulated python. When a predator is spotted, the macaque will let out a short, hoarse bark to notify others of the danger.
Locally, the Pagai Island macaque is known as the bokkoi. They, along with other Mentawai primates, were once believed to be an intermediary between locals and their ancestors.
With a group size of 5 to 25 individuals, the Pagai Island macaque troop consists of one adult male and several females, along with infants and juveniles. These one-male-multiple-female groups are often referred to as harems. Adult males that do not have their own harem are solitary and will often challenge harem leaders in order to gain females for themselves. These challenges can result in aggressive fights and injury. The male leader of a harem is dominant to all other members, and will communicate this to group members through loud, high pitched calls.
When foraging, the troop will split into smaller groups, but still tend to migrate in close proximity to other small-groups. They have been known to have a commensal association with Mentawai langurs (Presbytis potenziani) and pig-tailed langurs (Simias concolor), foraging alongside the two species. They are a diurnal species, meaning they are awake during the day, with the exception of naps, and sleep during the night. They are known to sleep in small-groups, similar to how they forage.
The Pagai Island macaque is an expressive primate that communicates through many modes. As with many primates, especially other macaques, the most striking mode is their open-mouth stare that signals aggression. In this communication tactic, the monkeys’ formidable canines are on full display, showing that they are ready for a fight should they need to protect themselves or others. Screeching or loud barks are often accompanied by this open-mouth stare. When their tails are high in the air, this can signal that they are alert, or, for females, it may indicate sexual readiness. Males hold the highest position in the group and will communicate to others through loud, high-pitched calls.
Courtship among Pagai Island macaques is not an intricate dance, as is seen in many other species. Generally, sexual mates are known to one another for an extended period, sometimes their whole lives. Females reach sexual maturity around the age of three years, while males reach it at around five years. Females’ sexual readiness is gleaned by the swelling and reddening of their genitals. Following this, they may crouch in front of males to encourage copulation. Pregnancy lasts for five to six months and females give birth to one infant at a time—usually in the middle of the night. Once born, the female licks the infant clean; mothers have been observed eating the placenta after birth.
Infants rely heavily on their mothers, and as they age they will retain a close bond. Mothers and daughters tend to have life-long bonds, as females stay in the group. Mothers and sons, however, have a close bond until they reach sexual maturity and leave the group.
Like many frugivores, the Pagai Island macaque’s ecological role is that of seed disperser. As mentioned previously, they prefer to eat the ever-abundant figs that grow on the Mentawai Islands. Upon eating and digesting these fruits, Pagai Island macaques will drop the seeds in their feces. This extends the fig tree’s propagation greatly and helps contribute to the genetic diversity of the tree species. This is vital on islands, where the genetic pool can become small over just a few generations.
The Pagai Island macaque is currently listed as Critically Endangered (IUCN, 2015), appearing the International Union for Conservation of Nature’s Red List of Threatened Species. Their population is decreasing, with an estimation of only 2,100 to 3,700 individuals left in the wild, and it is estimated that they will have lost 80% of their population from 2002 to 2040.
Unfortunately, they do not occur in any protected areas. Their greatest threat is hunting and commercial logging. On Sipura, only 10–15% of the original forest exists, with the rest being cleared for logging or building. Due to the ever-increasing immigration to the islands, much of the natural forest is being cut down in order to support cash crops and palm plantations. This deforestation causes water levels of the rivers to fluctuate, which has subsequently resulted in higher instances of malarial mosquitoes. The Pagai Island macaques’ habitat is also affected by roads, as they sever the landscape and their home ranges.
Instances of hunting have increased in recent years as well. For a long time, the human population used bows and arrows; however, they are now equipped with .177 caliber air rifles. These monkeys are not usually killed for sustenance use, though, but rather because they are seen as crop pests. Entire troops have been captured and killed by the use of traps, which has a profound effect on the population. The need for protection of this species is vital and urgent.
The Pagai Island Macaque is listed in Appendix II of the Convention on International Trade in Endangered Species (CITES), an international agreement between governments whose goal is to ensure that international trade in specimens of wild animals and plants does not threaten their survival.
As previously mentioned, this species does not occur in any protected areas. However, they do occur in areas that have been suggested for protection, such as the Betumonga Research Area, and the Sinakak Islet area. To complicate species preservation further, there is no viable captive population—meaning the preservation of the wild populations is absolutely vital for this species to survive. Supporting sustainable logging companies, conservation education, and alternative economic options for local people to avoid selling their land are just a few of the suggestions in a 2006 action plan. The IUCN suggests area and habitat protection, site and species management, legislation, conservation education, and trade management as being among the most pressing. Additionally, there is more research needed for this species to better protect and preserve them.
Historically, primates on the Mentawai Islands have been loved and celebrated. Locals believed they were an intermediary to communicate with ancestors. Hunting, however, also has deep historical roots in the area. Now with subsidies and incentives, many people are moving out of the forest and into the cities, selling their land. People who once would have acted as protectors of the natural environment are being forced to move because of the logging and crop business. There are non-profits in the area that are currently working on a teacher-training curriculum, in which teachers are empowered to educate local communities about primates. The first teacher training happened in 2020 and it was attended by a dozen teachers, as well as elders in the community. Grassroots activism such as this is critical in preserving species.
Written by Robyn Scott, September 2023