Spectral tarsier, Tarsius spectrum
SPECTRAL TARSIER
Tarsius spectrum
Geographic Distribution and Habitat
The spectral tarsier lives in Sulawesi, Indonesia. They are endemic to the island, meaning that it is the only place in the world where this species occurs naturally. They can be found across the island in primary and secondary forests, and some agricultural outcrops. Non-forest habitats that they occupy are tickets of grass, shrubs, bushes, thorn scrubs, and generally any dense vegetative areas. They have a small home range, which is the area in which they travel in a day, of only 2 acres (1 hectare). They spend their time in the lower canopy of the forest, often just a few feet (a couple meters) from the ground. The spectral tarsiers’ ability to live in varying degrees of human disturbance is a beneficial adaptation, as they are affected by deforestation.
Tarsiers have a fraught taxonomic history. Initially classified as prosimians due to their small size, nocturnal habits, and features like toothcombs and toilet claws—traits typical of the Strepsirrhini suborder—several physical traits indicate a closer relationship to simian primates (apes and monkeys). The most notable of these is their dry noses, which they share with apes and monkeys, placing them in the Haplorrhini suborder. Additionally, tarsiers possess a “detached” lip like simian primates, enabling them to express a wider range of facial expressions compared to prosimians. Tarsiers are regarded as an intermediate form of primate, falling within their own intraorder, Tarsiiformes.
There are three genera of tarsier. Carlito and Cephalopacus, each with one species, and Tarsius which contains twelve species. The phylogeny, or evolutionary family tree, of tarsiers is often debated. They are considered a cryptic species, which means that many of the species look strikingly similar to the human eye.
Size, Weight, and Lifespan
Tarsiers are among the smallest primates in the world. They are sexually dimorphic, meaning that their appearance and size are dependent on their sex. For these tarsiers, that means males are slightly larger than the females. Males are around 4 inches long (10 cm) while females are roughly 3 inches long (7.6 cm). Their tails add an additional 7.8 to 10 inches (20 to 26 cm) to their petite bodies. They weigh around 3.5 to 5.3 oz (100 to 150 grams). It’s believed that in captivity the spectral tarsier can live to be around 17 years old, while in the wild they most likely live to be 14 to 16 years. Age can often be seen on a tarsier by the graying of their hair.
Appearance
The spectral tarsier has an unmistakable appearance. They have medium brown fur that is consistent all over their bodies, except for a small, lighter patch of hair on their chest and stomachs. They have large, mobile ears that can be rotated in order to catch the best audio around them. The spectral tarsier has a small, mousey nose. Lastly, and arguably their most distinct feature, are their eyes! These tarsiers, along with all tarsiers, have incredibly large eyes compared to their skull size. In fact, tarsiers have the biggest eye-to-skull ratio of any other mammal. These big, beautiful eyes are what allow the spectral tarsier to have such incredible night vision. While many nocturnal species have a component of the eye that allows for night vision, the tapetum lucidum, tarsiers lack this anatomical feature. Instead, they adapted to see in the dark by having larger-than-life eyes. While these eyes are fantastic for spotting and catching prey, they do come with some hindrances. For example, the spectral tarsier is unable to move its eyes, which means that in order to look in different directions, it must completely turn its head. But, this is no issue for the tarsier—since they can turn their heads about 180 degrees!
Another notable feature of the spectral tarsiers’ appearance is that of its limbs and digits. These small primates have incredibly long fingers which allow for a steady grasp on trees and bushes, while also providing the needed dexterity to catch prey. They also have an elongated tarsus bone, which is how they get their name. The tarsus bone is located in the ankle and allows for spring-like action. This is useful for bouncing from tree to tree.
Diet
Tarsiers are unique among primates. They are the only exclusively carnivorous primate. Spectral tarsiers particularly enjoy moths, locusts, cicadas, grasshoppers, and beetles. They will also enjoy small lizards and snakes if they’re able to get their long fingers on them. Because of their specialized diet, their body reflects all the adaptations that allow them to excel in their niche.
Behavior and Lifestyle
Spectral tarsiers are nocturnal, meaning that they wake in the evening or night, and are active throughout the dark hours. They spend their time foraging, traveling, and socializing. They have been described as having “lunar philia” which essentially means that they are especially active when the moon is fuller. This is most likely because they lack the tapetum lucidum which allows for true night vision. Therefore, the moon simply makes it easier to see and navigate the forest.
Tarsiers rely on smell more than monkeys or apes. Because of this, they will scent-mark with urine. It’s not uncommon for males and females to both do this, however, it is more often seen in males. They will also urinate on their hands to spread their scent, and also to give them an extra sticky grip while jumping from place to place.
The spectral tarsiers’ unique morphology contributes to some of their behaviors. Their long fingers have disc-like pads on the tips, which allows them to almost suction to whatever they’re grasping. Additionally, because of their elongated tarsus bone, they can jump around 40 times the length of their own bodies! That would be like a human being able to jump roughly 68 feet (62 meters)!
When a predator comes into view, they will often scatter and hide. However, they have been observed mobbing certain predators, such as snakes. Mobbing is when multiple individuals surround and harass the predator until it is either killed or forced to retreat. This behavior has been associated with less predation by the mobbed predator species.
Spectral tarsiers do not seem to recognize the vocal duets of another tarsier species, Dian’s tarsiers, even though they share the same territory.
Spectral tarsier society is still being researched and understood. We know that males and females both live together. Males travel further distances than females and seem to maintain a boundary of their range, making sure opposing groups are aware of their presence by scent marking. They are considered territorial, and such encounters usually involve males posturing at one another. Females are incredibly effective hunters and are usually more successful than males in their hunting endeavors.
Group members enjoy spending their time together. They allogroom, which is the act of grooming another individual, play, and even sing! Duets are common among spectral tarsier pairs, though they are often performed at a pitch that is difficult for the human ear to hear.
It is thought that tarsier sociality is dependent on the environment and the resources available to them. If they are living in a depleted forest, for example, they will not be as gregarious or have as many group members.
Spectral tarsiers nest together. This essentially means that they will huddle together and snuggle while they sleep. They also groom, allogroom, play, and vocalize while at their sleep sites. Adolescent spectral tarsiers have been observed “babysitting” infants during travel and foraging. This behavior would allow the mother of the infant to forage for herself.
As mentioned earlier, many of the vocalizations the spectral tarsier makes are at a pitch that the human ear cannot hear. It was because of this that researchers thought they were a largely silent primate. However, due to the world’s leading researcher on tarsiers, Dr. Sharon Gursky, we now know that ultrasonic vocalization is common for these small tree-hoppers. Ultrasonic vocalizations can only be heard at short distances, and Gursky identifies this as a type of echolocation—which is another aid for their nocturnal navigation. Gursky classifies the vocalizations as chirps, twitters, choruses, doubles, and whistles. These calls are used in a variety of ways, sometimes to duet with potential mating partner, or to warn group members of a threat.
Spectral tarsiers are monogamous during mating season, though they may split from this pairing after the birth of an infant. Males and females sing together during this season of monogamy, which is a way they stay closely bonded. Spectral tarsiers have mating seasons twice per year. The first is April through June and the other is October through November.
Before copulation, the male and female may take turns sniffing one another’s genitals, and they may even urinate during this process. The male will chirp, and they will sniff, and this cycle may last as long as 60 to 90 minutes. Copulation, however, lasts a little under two minutes. When the male and female are done, they may engage in post-copulatory behavior, such as the male cleaning his genitals and the female rubbing her genitals on nearby branches or objects. After a 6 months gestation (pregnancy), she will give birth to a single infant.
Infant tarsiers are quite advanced in their abilities from an early age. They can be seen venturing on their own travels as young as 23 days old.
When the spectral tarsier is older, both the males and females will disperse from their natal group, though males will eventually venture further than the females. Dispersal from the group the individual was born in gives it a better chance at finding a partner, as well as avoiding inbreeding.
It has been said that spectral tarsiers have the same ecological role as owls. They act as a forest’s pest control, aiding the trees around them by eating predators. They also act as prey for a variety of snakes and birds.
The International Union for Conservation of Nature lists the spectral tarsier as Vulnerable (IUCN, 2015), appearing on the IUCN Red List of Threatened Species.
As with most primates, the habitat of the spectral tarsier is under threat. Agriculture, limestone mining, illegal logging, and agricultural pesticides are just among some of the threats that these small primates face. Some spectral tarsiers are sold as pets, although luckily it does not seem this is happening on an international scale. Spectral tarsiers live all across Sulawesi, which is fortunate for the species. However, due to their cryptic status, the full extent of species loss may not be realized just yet.
Due to the spectral tarsier’s lack of local protections and no protected areas, some argue that their conservation status should be changed to Critically Endangered.
The 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.
Unfortunately, there do not seem to be many conservation initiatives in place. There are many actions that should be taken, such as protecting the areas they live, education and awareness, and a species management plan. Continued research and monitoring on how this species lives will also help in understanding their unique needs and how humans can take care of the habitat they live in.
- https://www.lembehresort.com/resort/spectral-tarsier-tarsius/
- https://www.britannica.com/animal/South-Sulawesi-tarsier
- https://www.inaturalist.org/taxa/1064525-Tarsius-tarsier
- https://www.ecologyasia.com/verts/mammals/spectral_tarsier.htm
- https://primate.wisc.edu/primate-info-net/pin-factsheets/pin-factsheet-tarsier/
- https://link.springer.com/article/10.1007/BF02692280
- https://onlinelibrary.wiley.com/doi/abs/10.1002/(SICI)10982345(200005)51:1%3C89::AID-AJP7%3E3.0.CO;2-7?casa_token=oKcqA5dGgOUAAAAA%3AEcLHhHYaiZxiZI85zDHYSrX7jeR-Ae36kLwyfK_4h2YEiujcCKxFAyqfnop3plbyI3n2bvSYzUpmjCk
- https://link.springer.com/article/10.1007/BF02736071
- https://www.iucnredlist.org/species/162369551/17978304
Written by Robyn Scott, October 2024