Gursky’s Spectral Tarsier, Tarsius spectrumgurskyae
GURSKY'S SPECTRAL TARSIER
Tarsius spectrumgurskyae
Geographic Distribution and Habitat
Gursky’s spectral tarsiers (Tarsius spectrumgurskyae), known locally as wusing, are endemic to the tropical Indonesian island of Sulawesi (also known as Celebes), east of Borneo. The island’s northern peninsula is home to these tiny primates. Except for captive individuals kept by zoos, Gursky’s spectral tarsiers live nowhere else in the world.
Their habitat is provided by various forest types including primary, secondary, mangrove, and so-called forest gardens (or agroforestry) composed of trees, shrubs, and perennial plants cultivated by humans to mimic the structure of the surrounding forest. Though these opportunistic tarsiers might take advantage of this created, sustainable ecosystem (finding shelter and food sources), they are likewise relegated to habitats less desirable due to human disturbance. They reside at elevations from ground level up to 3,609 feet (1,100 meters).
Prior to attaining distinct species status in 2017, Gursky’s spectral tarsier had been classified as the spectral tarsier (Tarsius spectrum), based on the primate’s behavioral ecology resulting from studies performed by anthropologist Dr. Sharon Gursky. Later studies that focused on differences in vocalizations and pelage led to the taxonomic revision that today separates those tarsiers in Gursky’s study population—who would become known by the species’ namesake, “Gursky’s spectral tarsier”—from the spectral tarsier and other tarsier species. No subspecies have been identified.
Tarsiers Are Unique Primates
The tarsier family (Tarsiidae) includes 3 genera, at least 14 species, and 7 subspecies. However, the taxonomy of the species continues to be debated.
Tarsiers are, somewhat controversially, categorized as prosimians who share the suborder Haplorrhini with their dry-nosed simian cousins: monkeys, apes, and humans.
Haplorrhines are considered to be less primitive than their prosimian cousins belonging to the suborder Strepsirrhini, or “wet-nosed” primates. Strepsirrhines include lemurs, aye-ayes, lorises, and galagos (bush babies).
Haplorrhines diverged from Strepsirrhines 63 million years ago.
While 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
These are among the tiniest primates. Maximum head-to-body length for adults is only 5.5 inches (14 centimeters). Their nonprehensile tail adds another 9.4 inches (24 centimeters) to the frame. Weighing a mere 4.6 ounces (0.13 kilogram), Gursky’s spectral tarsiers barely tip the scales.
Most tarsier species are sexually dimorphic, with males typically being a bit larger than females. (Pygmy tarsiers might be the exception, with some scientific accounts suggesting that the females are slightly larger than males.)
Lifespan is not recorded for this species. We could hazard a guess by looking toward the spectral tarsier, who has a lifespan of 14 to 16 years in the wild. Or we could take a cue by looking at ourselves in the mirror. Like us humans, as tarsiers age their hair tends to turn gray.
Appearance
Let’s get the obligatory comparison to Yoda of Star Wars fame out of the way. Yes, there is a strong resemblance, and there are those who claim that tarsiers are the inspiration for the fictional alien Jedi character of this movie franchise. Perhaps.
With the word “spectral” in its name, you would expect this little primate (who looks like a cross between a chinchilla and a vampire) to have a phantasmal or supernatural appearance. And you’d be right. Mother Nature has fitted this gremlin-like creature with giant-sized, golden orbs for eyes that she then outlined with black circles (as if the eyes needed to be any more prominent). These outlandish orbs overtake the tarsier’s grayish-orange furred face—dominating a demure, pinkish muzzle with its few stray, white whiskers. Extremely sharp teeth, akin to those of a bat, fit inside the mouth. Crazy, big ears fan upward from each temple.
“Tarsier” refers to the primate’s exceptionally long tarsal bone–actually a group of seven bones (tarsi) that form the ankle and hind foot. Its vampire-like fingers and toes are bony, long, and thin. The third finger of a Gursky’s spectral tarsier is about the same length as its upper arm. And the second and third toes on each foot are fitted with a long, curved claw (known as a toilet claw) used for grooming. Its long, scaly tail is topped off with a black tuft of fur on the tip. The pelage is thick and plush, cloaking the round, compact body with a gray undercoat and top hairs that are painted orange.
Captivating and otherworldly in appearance, the Gursky’s spectral tarsier is a spellcaster.
Diet
Tarsiers have the distinction of being the only faunivorous primate species—a science-y way of saying that their diet consists 100 percent of live animal prey. As faunivores, they feed on other animals—fauna—within their specific ecosystem. Yes, this predilection also makes tarsiers carnivores, but with a twist. While carnivores eat the flesh of their prey, faunivores eat all parts of an animal: bones, fur, feathers . . .
Do you know who else are faunivores? Owls. An owl will swallow its prey whole and later regurgitate bits of undigested bones and other bodily materials.
Gursky’s spectral tarsiers feed mostly upon insects, including moths, crickets, and grasshoppers. Lizards, frogs, birds, bats, and other small vertebrates complement the species’ meal plan.
Behavior and Lifestyle
These are nocturnal and arboreal primates, meaning they are active during the night and spend the majority of their time in the trees. Residing mostly in the lower canopy, often close to the forest floor, tarsiers have supremely adapted to their environment to become skilled, stealthy predators. Their keen senses also help them to evade becoming prey themselves.
Although they lack a tapetum lucidum—a reflective layer of tissue behind the eye’s retina of certain animals that helps them to see in low light—tarsiers’ enormous eyes and a specialized brain with a large visual cortex enable them to see in the dark so they can catch small prey. Impressively, their neck rotates 180 degrees in each direction, giving them an all-around, 360-degree view of their surroundings—more than compensating for the limited movement in their forward-facing eyes. Other adaptations include acute hearing as evidenced by the constant movement of their large ears, which act like satellite dishes as they pivot toward the sounds of nearby insect prey.
Tarsier locomotion is characterized by vertical clinging and leaping (VCL). Fleshy pads on the tips of their bony fingers and toes help tarsiers to cling vertically to tree trunks and branches. When clinging upright to a tree, they press their long tail against the trunk for support. Dermal ridges on the tail’s underside provide necessary traction. Their tail also assists with balance while standing upright on a branch, and when they propel themselves forward to make their impressive leaps. Powerful muscles in their long legs in conjunction with their long tarsi (ankle) bones assist them in leaping easily from tree trunk to tree trunk in the forest understory, at astounding distances up to 19.7 feet (6 meters). A fused tibia and fibula help them to stick their landing, acting as shock absorbers. With speed and accuracy, they pounce upon their prey.
A tarsier has the largest eye-to-body size ratio of all mammals; each eye is as large as, or larger, than its brain.
These are social primates who live in small, family groups of up to 11 individuals, usually with more than one adult male and female. While dispersal has not been reported for Gursky’s spectral tarsiers, their close cousin the spectral tarsier (Tarsius spectrum) is reported to disperse (leave home) upon reaching adulthood; males travel farther than females. Dispersal helps to avoid inbreeding.
Gursky’s spectral tarsiers often share their small home range of 2 acres (1 hectare) with another group. To avoid territorial disputes, tarsiers scent-mark their borders with secretions from glands located on their upper abdomen and with their urine.
Though they are nocturnal creatures, Gursky’s spectral tarsiers don’t rush their schedule. Typically, they emerge from the safety of their daytime lair at dusk and spend an hour gearing up for the evening’s activities. They travel as a group, for there is safety in numbers. Mothers “park” their infants nearby while they forage for food. Traveling and foraging are interspersed with rest periods. If they must, tarsiers will descend to the ground for water.
Shortly before dawn, they call it a night and find a tree hole for their daytime slumber, sleeping together in small groups, usually a breeding couple and their juvenile offspring. (One sleeping site and two or three alternate sites are common.) They choose tree trunks with dense vegetation and complex vertical root structures that allow them to hide from predators. Because of their small size, tarsiers are vulnerable to a host of larger predators, who include snakes, birds of prey, civets, monitor lizards, and domestic dogs and cats.
Sympatric species include a marsupial known as the Sulawesi bear cuscus (Ailurops ursinus), the whitish dwarf squirrel (Prosciurillus leucomus), two species of anoa (also known as “midget buffalo”): the mountain anoa (Bubalus quarlesi) and the lowland anoa (Bubalus depressicornis), both who are classified as Endangered; the crested macaque (Macaca nigra), close cousin the spectral tarsier (Tarsius spectrum), the Sulawesi flying fox or Sulawesi fruit bat (Acerodon celebensis), antelopes, deer, crocodiles, snakes, monitor lizards, civets, and a bevy of exotic bird species who include the green-backed kingfisher (Actenoides monachus), green imperial pigeon, (Ducula aenea), the Sulawesi lilac kingfisher (Cittura cyanotis), and Sulawesi hornbill (Rhabdotorrhinus exarhatus).
Gursky’s spectral tarsiers have flexible call patterns, emitting different notes. Vocalizations include trills, twitters, alarm calls (to warn group members of potential danger), and duets between a paired adult male and female. The devoted couple sings their duet, which sounds like birdsong, just before dawn as they retreat to their daytime sleeping site. It begins with the male singing a series of short, vibrating notes; the female joins him by singing a series of high-pitched notes that dip down to a lower pitch and then rise again to a high-pitched for a finale that coalesces with the notes of her mate. On occasion, juvenile offspring might join in, turning the duet into a family chorus.
Whether a couple engages in duet to announce their territory, declare their bonded status to deter suitor wannabes, or simply to declare their devotion to one other . . . are all theories posited and still being studied by wildlife biologists. One point with general concurrence: these virtuoso duets are physiologically and neurologically taxing. Thus, a certain level of physical fitness is necessary to perform their duet well. Scientists liken the capability and “virtuosity” of singing these notes, of both the male and female tarsier, to the similar significance of a (male) peacock’s tail—an elaborate, vibrant, visual signal of fitness and a prime example of sexual selection in nature.
Olfactory communication is through scent marking. Usually, it’s a group’s males who are entrusted with this activity as they patrol territorial boundaries. If said boundaries are not respected, Gursky’s spectral tarsiers have reportedly chased and lunged at intruders. As a group, they’ve mobbed a predator.
Tactile communication includes play sessions, hugging one another, and allogrooming (the practice of grooming one another, an important activity that helps to instill strong social bonds with each other). In a gesture of etiquette, these tarsiers are even known to share their food with one another.
Gursky’s spectral tarsiers are thought to be mostly monogamous (having one mate). But some researchers have posited that a devoted couple might split after raising their young to take on a new mating partner (which would suggest, or at least flirt with, a polygamous mating system).
We have to look to the spectral tarsier for further clues on reproduction.
Spectral tarsiers attain sexual maturity at about 17 months of age. They breed twice a year, from April through June and October through November. Males and females reportedly sing together during mating season. Foreplay consists of sniffing one another’s genitals and some “chirping” by the male (a serenade?) before they do the deed, which lasts less than 2 minutes.
Following a gestation period of about six months, a female gives birth to a single infant who is born fully furred with its eyes open. Amazingly, newborns are able to climb within a day of birth—though, for their first three weeks of life, they are carried in their mothers’ mouths as they travel. Other group members, including subadults and adult males, may lend assistance with infant care (known as alloparenting).
Mothers lactate (produce milk) for up to 80 days, though their young are considered weaned between 4 to 10 weeks of age. After weaning, young spectral tarsiers are considered independent and they begin hunting on their own.
Though they’ve yet to be ceremoniously recognized (or credited) as farmers’ helpers, Gursky’s spectral tarsiers might inhibit this role. Their voracious appetite for insects who are considered crop pests, grasshoppers in particular, benefits crop cultivation.
Gursky’s spectral tarsier is classified as Vulnerable by the International Union for Conservation of Nature (IUCN, March 2020), appearing on the IUCN Red List of Threatened Species. A total population number is not given, but wildlife studies report that in pristine, undisturbed habitat, the estimated population density is 156 individuals per 0.39 square mile (1 square kilometer.) Unfortunately, pristine habitat is disappearing.
Habitat loss due to illegal logging is the primary threat to the species’ survival. More than 30 percent of its natural rainforest habitat has been converted into agricultural tracts of land over the past 20 years (approximately three generations). While these tarsiers are able to adapt to small-scale agroforestry, selective logging, and disturbed forests, their lives are in continuous peril by the removal of their habitat—the trees they so heavily rely on and that sustain them.
Poisoning from the ingestion of agricultural pesticides and predation by free-roaming domestic dogs and cats are additional anthropogenic (human-caused) threats. Gursky’s spectral tarsiers can also be victims of the illegal wildlife trafficking and the pet trade. Captive tarsiers fare poorly; those individuals who are kidnapped to become someone’s pet usually die shortly after capture.
Gursky’s spectral 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. In theory, they are also protected by national law.
The species is found in several conservation or protected areas, predominantly within Tangkoko Batuangus Nature Reserve (also referred to as Tangkoko National Park). But even within this so-called protected area, habitat loss poses a threat to Gursky’s spectral tarsier and to the other wildlife species who live here (other species also face the risk of being poached for their flesh, known as bushmeat).
Conservationists wishing to preserve for future generations Sulawesi’s flora and fauna—which they describe as the country’s most precious, natural treasures—stress the need and urgency for improved management within protected areas. Their plea has been in stark contrast to the historical position of some local government officials, who have been accused of viewing pristine forests as “a source of quick and easy cash.” To point, one legislator arrested in 2008 was convicted of receiving bribes in exchange for removing the protected status of certain forests.
Indonesian and international environmental organizations working together for the park’s conservation include Sulut Bosami, Tarantula, and the Wildlife Conservation Society.
Conservationists further urge the creation of a public education campaign to instill in the local population a pride and reverence for Sulawesi’s flora and fauna and to dispel the misconception that Gursky’s spectral tarsiers are crop pests—when in reality, as we have seen, they may be helping protect crops by eating insect pests.
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Written by Kathleen Downey, March 2025