Siau Island Tarsier, Tarsius tumpara
SIAU ISLAND TARSIER
Tarsius tumpara
Geographic Distribution and Habitat
The tiny volcanic island of Siau, in Indonesia’s North Sulawesi province, is home to a tiny, enigmatic primate. Siau Island tarsiers (Tarsius tumpara) are found nowhere else in the world. Making their home on the tiny island of Siau Island, some scientists speculate that these Critically Endangered primates may also inhabit some of the smaller islands in close proximity to their home, separated only by shallow ocean. Siau Island is only one-fifth the size of Singapore, and about 55% of the island is dominated by Mt. Karangetang, one of Indonesia’s most active volcanoes. The looming presence of this volcano diminishes the available habitat of the Siau Island tarsier significantly. Although there are rumored reports of Siau Island tarsiers residing near the volcano’s caldera, surveys from 2009 cite evidence of dwellings in only two places: on the shores of a small freshwater pond at the extreme southern end of the of the island, and on a steep cliff face along the east coast road that runs parallel to the ocean. While they have only been recorded directly at these two locations, based on other tarsier species, scientists can conclude that Siau Island tarsiers may also dwell in mangrove forests, secondary forests, forest gardens, and a variety of shrubland regions altered by human disturbances. Additionally, inhabiting altitudes of up to 1968.5 feet (600 m).
In 2008, the Siau Island tarsier was classified as a distinct tarsier species. When they were first surveyed in 2002, Siau Island tarsiers were thought to be a population of Sangihe tarsiers (Tarsius sangirensis), who inhabit Sangihe Island (also known as Sangir Island). Both Sangihe and Siau Islands are part of the Sangihe Islands archipelago, a volcanic arc island chain in the Sulawesi Sea stretching 124 miles (200 km) north from the northern tip of Sulawesi. Sangihe Island is 37 miles (60 km) to the north of Siau Island, across ocean depths greater than 3,281 feet (1,000 m).
More generally, the tarsier family (Tarsiidae) includes 3 genera, and at least 14 species and 7 subspecies. However, the taxonomy of the species continues to be debated.
Tarsiers are prosimians who belong to the suborder Haplorrhini, or “dry-nosed” primates, along with the true simians (monkeys, apes, including humans). Haplorrhines are considered to be less primitive than those belonging to the suborder Strepsirrhini, or “wet-nosed” primates. Strepsirrhines include lemurs, aye-ayes, lorises, and galagos (bushbabies). Haplorrhines diverged from Strepsirrhines 63 million years ago. After this diversion, strepsirrhines retained their ability to make Vitamin C; haplorrhines (including tarsiers) did not. Another distinction between the two is the “disconnected” upper lip that characterizes haplorrhines, allowing for their facial expressions.
Some scientists believe that tarsiers deserve a narrower taxonomic classification, asserting that tarsiers occupy a small evolutionary branch between haplorrhine simians and strepsirrhine prosimians.
Size, Weight, and Lifespan
Siau Island tarsiers measure just 4 to 6 inches (about 10–15 cm) in head-to-body length. A rope-like, nearly hairless tail adds another 8 inches (20 cm). A skeletal wonder of unusually long, articulating tarsus bones gives these tarsiers their excessively long rear feet (“tarsus” happens to be the word origin of the name “tarsier.”)
Weight has not been recorded for the Siau Island tarsier; however, a closely related species, the Sangihe tarsier, weighs between 3.5 and 4 ounces (0.1–0.12 kg).
The lifespan of the Siau Island tarsier is unknown. However, for other members of the genus Tarsius, such as the spectral tarsier, also known as the Sulawesi tarsier (Tarsius tarsier), lifespan in the wild is between 8 and 12 years; for the Philippine tarsier (Tarsius syrichta), lifespan in the wild is up to 24 years, but only 12–15 years in captivity. In the wild, Horsfield’s tarsier (Tarsius bancanus) lives 15 years. Taking these other lifespans in mind, the range of lifespan that scientists can assume for the Siau Island Tarsier lies at around 8-24 years of age.
Appearance
Siau Island tarsiers bear a resemblance to Sangihe tarsiers, with slight variations in coat color. Instead of a golden-brown coat, like that of Sangihe tarsiers, Siau Island tarsiers are cloaked in a brownish-gray pelage, which is common to other tarsiers. Instead of the nearly white underside that distinguishes their sister species, Siau Island tarsiers have a gray underside. A dark gray ring outlines its gray, furry face, and a prominent brown line encircles each eye.
Imp-like, cartoonish, less-kind folk might say “ghoulish”—are all apt descriptors of this diminutive critter. Most notably, the tarsier’s eyes are exceptionally large. Each eye is larger than the animal’s brain and, together, they give the skull an unusual shape. The pupils sit small, centered, and overwhelmed by the irises, which are varying shades of goldish-brown. Because of their size, a tarsier’s eyes cannot move in its head. To compensate for this, they can move their heads a full 180° in each direction. It may, therefore, appear that he is looking at you with a wide, fixed gaze. In addition to the piercing gaze, the tarsier’s enormous eyes assist nocturnal activities with enhanced night vision.
Unusually, unlike many nocturnal animals, tarsiers’ eyes lack the light-reflecting layer known as the tapetum lucidum. Instead, similar to humans, their eyes are equipped with closely packed cones, or photoreceptor cells. This adaptation gives them sharp central vision, also known as “foveal” vision. The upper lip is not directly connected to the nose, allowing for a wide range of facial expressions. To further help them navigate at night, Siau Island tarsiers also have large, ridged ears to pick up any sounds from looming predators. Bat-like ears, spindly fingers, unusually long feet, and its long, skinny tail complete the Siau Island tarsier’s unique appearance.
Diet
Siau Island tarsiers are insectivores, a fancy way of saying that they eat mostly insects. Their favorite insects are katydids and moths. They are fond of spiders, too. Frogs, lizards, and the occasional small bird and bat are also on their menu. Their wide mouth, relative to their small size, accommodates larger prey. Strong jaws and sharp teeth are adaptations to their strictly carnivorous diet: tarsiers are the only completely carnivorous primates in the world!
Behavior and Lifestyle
Arboreal creatures, Siau Island tarsiers spend virtually all their time in trees. They are excellent climbers and even more impressive as jumpers; an adult can jump nearly 10 feet (3 m) high! Their agility is a great asset when capturing prey, and their ability to rotate their head 180 degrees in each direction spells doom for nearby bugs. Further honing their hunting skills, these tarsiers also have very keen hearing. Rather than forage, like most insectivores, tarsiers patiently wait on a branch for an unsuspecting bug to appear, then jump toward it. Their large rear feet assist them in this feat. They might also reach out, and with great vertical strength, grab flying prey with their long, spindly fingers; Siau Island tarsiers are known to snatch a bird in flight!
Prominent pads on their fingers and toes allow tarsiers to “stick their landing”—like gymnasts do—as they jump from tree to tree during their nightly travels. Like all tarsiers, Siau Island tarsiers are fitted with two “grooming” claws on the second and third digits of their feet, designed to comb through their velvety fur.
Since Siau Island tarsiers are nocturnal, they while away the daylight hours sleeping in tree holes, high up off the ground. They tend to enjoy to make their homes in fig trees (Ficus) when available, and bedtime typically starts at 5 or 6 in the morning. Wildlife researchers suspect that individuals sleep in separate sites, particularly in disturbed habitats. This solitary practice, a contrast to their nightly social activities, appears to be deliberately intended to reduce the risk of predator attack on an entire family group.
Siau Island tarsier eyeballs are larger than their brain!
Tarsiers are the only fully carnivorous primate.
In the local language of Sulawesi, tarsiers are called Tumpara. The scientific name of the Siau Island Tarsier, Tarsius tumpara, was created to incorporate the local name.
A lone Siau Island tarsier skull, taken from the island by an explorer in 1897, is in the collections of the Dresden Museum, Germany.
Phylogenetically linked to other Sulawesi tarsiers (foremost, perhaps, to Sangihe tarsiers)—which is just a super “science-y” way of saying that these species are related to one another through evolutionary development—Siau Island tarsiers, as members of this primordial clan, live in small, monogamous or polygamous groups of two to six individuals. Much of the scientific speculation about the little-studied Siau Island tarsier is based on other tarsier species, whose members have been the subjects of more intense field research.
Humans are the tarsiers’ most lethal predators, and because they have been so systematically preyed upon by humans, tarsiers have made further behavioral modifications. To limit being captured by a predator, they limit their vocalizations and, according to researchers, never engage in more than a duet—no loud group choruses. Biologically, their bodies are built to evade anything that might hurt them. The scent mark left by Siau Island tarsiers, used to mark territory and communicate with other tarsiers, fades much more rapidly than other Sulawesi tarsiers. Within an hour, it has dramatically diminished, and within a day, the scent is nearly undetectable to the human or predator nose.
Like members of their sister species, the Sangihe tarsier, Siau Island tarsiers are known to engage in morning duets. Unlike Sangihe tarsiers, whose calls are characterized by two-note phrases, morning duet calls of Siau Island tarsiers are typically one-note, isolated phrases. One occurrence of a multi-note phrase was captured in a field recording, however.
Among Sangihe tarsiers, males emit a chirping note, while females emit a whistle note. They also vocalize threats. It is not documented whether Siau Island Tarsiers also vocalize in this way, but understanding the Sangihe vocalization can give us insight into the behavior of the Siau Island tarsier. In the same vein, it is a reasonable conjecture that these tiny primates, like their closely related species, make use of their grooming claws and engage in social grooming, an activity that helps to establish familial bonds with one another. The extent of this social grooming cannot be certain, however, as an example, social grooming in Horsfield’s tarsiers occurs only between mothers and their infants.
Scent marks are important in demarcating territory and conveying various messages to one another. While Siau Island tarsiers have adapted a dissipating scent mark (to avoid detection and predation by humans), Sangihe tarsiers leave a lingering scent to send messages to one another. Sangihe tarsiers’ scent is unique to each individual and helps members to recognize each member of their group. It is unclear if Siau Island tarsier scent marks are individualized in this way.
Siau Island tarsiers are nearly two years old when they reach sexual maturity (capable of siring and bearing offspring). Mating rituals are unreported in the species.
After a gestation period of about six months, a female gives birth to a single infant whom she nurses for eight weeks, until weaned. Infant Siau Island tarsiers are born furred and with their eyes open. Amazingly, they are able to climb a tree and jump within one day of being born!
Parental care is not described in the species, but similar species detail a close bond with mother and offspring.
As insectivores, it is plausible that Siau Island tarsiers help to keep the structure of insect communities in balance within their environment. As with all animals, they are an integral part of an environmental community and food chain, providing nourishment to their predators and culling the populations of their prey.
The International Union for Conservation of Nature lists the Siau Island tarsier as Critically Endangered (IUCN, 2015), appearing on the IUCN Red List of Threatened Species.
Their position in the world is made precarious foremost by humans, who have razed tarsier habitats and repurposed them for human use. The island of Siau has extremely fertile soil and is well known for its production of nutmeg and mace, devoting much of the available island space to crops. The island, about one-fifth the size of Singapore, contains a human population density of 120 people per square mile (311 people/km2). Virtually no primary forests remain on Siau Island, and few notable secondary forests remain, resulting in fragmented tarsier populations. Aside from the habitats destroyed by deforestation, the tarsiers are already restricted to a small area because of Mt. Karangetang, an active volcano that looms over the island, threatening to erupt. According to a spokesperson for the IUCN, “Depending on the magnitude of the eruption and the path of the lava flows, the population [of Siau Island tarsiers] could be severely affected or even possibly disappear.”
But humans are most responsible for the disappearance of Siau Island tarsiers. Besides razing and transforming tarsier habitats for their own use, one source claims that the human populace of Siau Island hunts and eats these primates, referring to the snack food as “tola-tola.” Feral cats and dogs, introduced by humans in the area, have been found to prey upon tarsiers as well.
Between habitat degradation and hunting, more than 80 percent of the Siau Island tarsier population has been wiped out (as reported by National Geographic). Their numbers continue to dwindle with locals reporting a considerable decline in population since the late 1900s. A 2009 study using geographic information systems (GIS) to remotely sense remaining habitat placed the population as being 1,358–12,470 individuals. Little is clearly known about the remaining population, with the wide range in numbers is attributed to technological inadequacies using GIS. More investigation is needed to understand how many Siau Island tarsiers are left.
The Siau Island tarsier 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. However, as is often the case with endangered species, laws created to protect them are largely ignored and difficult to enforce.
Currently, no specific conservation programs exist for Siau Island tarsiers. North Sulawesi, where Siau Island is located, is home to several protected areas, from national parks to nature reserves. However, these areas do not extend to Siau Island, offering no protection to the Siau Island tarsier. While direct conservation laws do not exist, Sulawesi bushmeat laws are in place. Hard to enforce and with trade still booming, North Sulawesi regularly poaches species native to those islands. Surprisingly, while Siau Island tarsiers are not one of the species named in bushmeat laws, their presence in markets has decreased since the 2000s. There is some record of local initiatives that are working to spread knowledge about the unique species that live in North Sulawesi. In 2016, one such group, called the Critical Ecosystem Partnership Fund, was recorded working with local organization Celebio to collect more data on tarsiers and alert local and government groups towards the issue. Other initiatives are unknown or have not been recorded.
Furthermore, virtually no ecotourism exists on the island. Tourism, however, has the potential to negatively impact this species. Tarsiers are shy, nervous animals and become stressed with human contact. Activities such as camera flashes, being touched, or being kept inside an enclosure overstress the animals, causing them to react with self-harm: they bang their head against the walls of their confinement, thereby cracking open their thin skull and killing themselves (this behavior is referred to as “tarsier suicide”).
Captive breeding programs have failed with tarsiers. “Ex-situ” conservation (conservation occurring outside a species’s ecological niche) does not appear to work with this genus. Researchers report on 146 tarsiers taken from their natural habitat and brought to North America or Europe to establish breeding programs—all the tarsiers died. (A record of a lone Siau Island tarsier who was captured alive in April 2002 reveals that the kidnapped individual died, in transit to a zoological museum in the Netherlands, in April 2005.)
Given the fragility of Siau Island tarsiers and their Critically Endangered classification, conservationists say that it is crucial that emphasis be placed on “in situ” conservation; that is, conservation within the animals’ natural environment.
Conservationists also call for continued taxonomic research; improved and intensified tarsier-tracking activities like those being conducted near Tangkoko Nature Reserve, North Sulawesi, Indonesia; and the creation of community-based programs. Helping locals to better manage their lands without destroying tarsier habitat and educating and instilling within local people a sense of pride for these large-eyed, diminutive primates are imperatives in saving Siau Island tarsiers from extinction.
The creation of reputable sanctuaries is another key imperative. Conservationists/advocates are particular about how these sanctuaries should be created and how they should operate. Sanctuaries should be modeled after the Philippine Tarsier and Wildlife Sanctuary (also known as the Tarsier Research and Development Center), located in Corella, Bohol, in the Philippines, and operated by the Philippine Tarsier Foundation, the main non-profit private organization in the Philippines that seeks to protect the Philippine tarsier. (Contrarily, The Loboc Tarsier Conservation Area in the Philippines is not an official sanctuary area, and it is not supported or run by the Philippine Tarsier Foundation. Tarsiers here are reported to be enclosed, at least some of the time, put on display for tourists, and are prone to tarsier suicide.)
Some conservationists have asserted that sanctuaries and tarsier tracking programs should be developed side-by-side to promote more effective in-situ and, possibly, successful ex-situ conservation.
If no conservation programs are developed, however, the future of Siau Island tarsiers (as well as other endangered species within the Sangihe Island chain) is bleak.
- Endangered Species International: Tarsiers https://www.endangeredspeciesinternational.org/tarsiersection/
- Edge of Existence: Siau Island Tarsier http://www.edgeofexistence.org/species/siau-island-tarsier
- Wisconsin National Primate Research Center http://pin.primate.wisc.edu/factsheets/entry/tarsier
- IUCN redlist: Siau Island Tarsier https://www.iucnredlist.org/species/179234/7636582
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- Critical Ecosystem Partnership Fund: Community-Based Conservation of Critically Endangered Siau Scops Owl and Siau Island Tarsier in Indonesia
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Written by Kathleen Downer, 2019; Updated by Nami Kaneko, Aug 2025