Horsfield’s Tarsier, Cephalopachus bancanus
HORSFIELD’S TARSIER
Cephalopachus bancanus
Geographic Distribution and Habitat
Native to Southeast Asia, the Horsfield’s tarsier is known by many names, including the western tarsier, Bornean tarsier, and tarsier de Bornéo in French. As their names suggest, the Horsfield’s tarsier can be found in Borneo, an island that is divided among Malaysia, Brunei, and Indonesia. They’re found along the north coast and within Borneo’s Bukit Baka-Bukit Raya National Park located in western Kalimantan. They can also be found in the Indonesian islands of Sumatra, Serasen, Bangka, and Karimata, among others.
This species lives in primary and secondary tropical rainforests and is typically found at elevations below 328 feet (100 m) in areas without intensive agriculture, including mangroves, scrubland, and the edges of forests. Some subspecies have been observed at 3,937 feet (1200 m) and above, particularly in Kelabit uplands in Northern Sarawak in Borneo.
They prefer to avoid open areas as their bodies are adapted to climbing and leaping, which makes them most comfortable in densely forested regions. They also sleep in trees rather than on the ground or in a nest.
The Horsfield’s tarsier is the only species in the genus Cephalopachus. Originally, they were part of the genus Tarsius, with all the other tarsiers, but distinctions in their adaptations led scientists to classify them in a separate genus altogether. Moreover, four subspecies recognized are recognized based mostly on their location. These subspecies are:
- Cephalopachus bancanus bancanus, the nominate species
- Cephalopachus bancanus saltator, the Belitung Island tarsier
- Cephalopachus bancanus borneanus, the Bornean tarsier
- Cephalopachus bancanus natunensis, the Natuna Islands tarsier
Size, Weight, and Lifespan
The Horsfield’s tarsier appears to have larger eyes and longer limbs than other tarsiers. All tarsiers have large eyes to ensure they can see in low-light conditions, as they have all evolved to be nocturnal.
The Horsfield’s tarsiers tend to be between 4.4–5.1 inches (11.4–13.2 cm) long from the head to the base of their tail. The tail is quite long, reaching about 7.8–9 inches (20–23 cm), which is more than double the length of their bodies. The long tails help them balance as they leap between trees in the habitat, allowing them to jump across great distances easily.
The only sexual dimorphism observed in this species is the slight difference in how heavy the males and females are. Male Horsfield’s tarsiers weigh between 3.8–4.8 ounces (110–138.5 g), while the females weigh between 3.5–4.1 ounces (110–119 g).
Horsfield’s tarsiers may live between 8–15 years in the wild, and a little more than 17 years in captivity. What is interesting is that among captive tarsiers, those approaching 12–14 years don’t show clinical signs of old age. More research is necessary, but we may find that, as a group, tarsiers live far longer in the wild than we expect.
Appearance
The Horsfield’s tarsier’s head is much wider than it is long, enough to accommodate its large, yellowish bulging eyes. Individuals of this species actually look much like baby Yoda from the iconic series in the Star Wars Universe, “The Mandalorian.”
Unlike Baby Yoda, Horsfield’s tarsiers are covered in fur, ranging from olive to a grayish brown. Their tails don’t have any fur, but they do have an adorable tuft at the end.
Their hands and feet also don’t have any fur. Instead, they’ve got padded digits to grip onto branches easily. They also have two grooming claws on each foot to help them comb through their fur. The rest of their nails are flat.
Their ears are thin, delicate, and almost bat-like, but happen to be rounded instead of pointed. They sit on either side of the Horsfield’s tarsier’s head, pointing straight upwards.
Diet
All tarsiers are carnivorous, and the Horsfield’s tarsier prefers insects like crickets, cockroaches, grasshoppers, ants, and beetles. Most of their diet comprises scarab beetles and crickets, but they can eat larger prey animals like lizards and even bats, birds, and snakes.
The Horsfield’s tarsier can eat a wide range of prey because of their powerful jaw muscles. These muscles allow them to open their jaws wide enough to accommodate their prey and have the strength to grind down the crunchy exoskeletons of insects to digestible mash.
Typically, a Horsfield’s tarsier will catch prey with his nimble fingers, sometimes grabbing it right out of the air and eating it from the head downwards to kill the prey without too much struggle. Tarsiers tend to have a low metabolism and lower body temperatures compared to other mammals of a similar size, who may be herbivores.
They source water from wet leaves, bamboo shoots, and the trunk of trees, and they rarely, if ever, head to pools of water on the ground because they might become easy prey there.
Behavior and Lifestyle
Nocturnal and arboreal, the Horsfield’s tarsier is active between sunset and sunrise, leaping, climbing, and jumping from tree to tree, hunting for food. They typically live and hunt alone since they are more or less solitary animals with small overlaps in territory for socialization.
The only time males and females of this species are found together is typically during mating. Female Horsfield’s tarsiers ensure they have space from the males by chasing them off if they get too close! This behavior is especially seen when they’re pregnant or feeding their babies because maternal Horsfield’s tarsiers don’t like anyone harassing their babies.
Horsfield’s tarsiers hunt in a strategy that involves waiting and watching for the right moment and grabbing for their prey. More often than not, they’re quite successful.
They’re most active early in the evening when they’re able to catch more prey, and later towards the sunrise, when they’re finishing up the last of their dinner before heading to bed in the branches. Despite their incredible eyesight, Horsfield’s tarsiers rely largely on their hearing to find and hunt down their prey.
Like other tarsiers, Horsfield’s tarsiers can rotate their head around to about 180 degrees, similar to owls!
Horsfield’s tarsiers wake up around dusk and begin their hunt. Mothers with infants still in their care may set the babies aside for safety while they hunt their prey.
In the early evening, these tarsiers are most active, as their prey are awake and moving around and they’re able to catch them. As the night grows, fewer prey are moving around, and this is when they catch nocturnal prey animals like bats.
They swivel their ears around constantly to keep an ear out for any potential danger. Once they’ve had their fill, they find branches at a comfortable height to sleep in.
Unlike Spectral tarsiers, who live in small groups, Horsfield’s tarsiers live solitary lives. Babies stay with their mothers until they can hunt for themselves but tend to have very little to do with their fathers. Social grooming is observed between babies and their mothers but not among random individual members of the species.
Male Horsfield’s tarsiers have territory that overlaps with that of the females, and they socialize in those spaces. This type of dynamic is called a noyau system, a social but not social nuclear dynamic between individuals of a species.
When it comes to vocal communication, Horsfield’s tarsiers are usually silent in the wild, but that doesn’t mean they can’t vocalize. This species produces several sounds, with some made only by the babies.
The frequencies of their sounds are sometimes incredible high-pitched vocalizations, like alarm calls and distress signals.
The most common sounds produced by the Horsfield’s tarsier that are audible to human beings are cheeps and whistles. Babies use these sounds to communicate with their mothers. They also squeak as part of their communication, a sound only produced by infant Horsfield’s tarsiers.
Among adults, whistles attract mates or indicate their territory to other adults. They may also cheep at other adults for similar reasons. They might scream at intruders in their territory to get them to back off. Other antagonistic sounds include alarm calls, distress calls, and hysteresis.
They also communicate chemically through their urine, which is used to mark territory.
These tarsiers are monogamous, with male Horsfield’s tarsiers chasing and calling after the females in their overlapping territories as part of the courtship that may last a couple of hours at a time. Female tarsiers may choose to accept the males they prefer and determine how much time they will spend with them.
The courtship period is usually observed around October to December. Once they become pregnant, female Horsfield’s tarsiers carry babies for about 180 days, which is fairly long for such a small species.
The babies are born fully furred and with their eyes open, and their mothers look after them, chasing away males who might want to harass them. The mothers carry their babies around with their mouths and sometimes keep them aside in safe spaces so they’re free to leap around and hunt easily.
These babies learn to hunt by watching their mothers and can hunt around six weeks. Their mother looks after them until they are properly weaned, around 8 or 9 weeks after their birth.
With insects being the majority of their diet, the Horsfield’s tarsiers play an important role in managing insect pest populations. This management is vastly important for the environment, people, and agriculture.
Horsfield’s tarsiers are also host to a specific kind of parasitic worm, the Moniliformis tarsii, that is found only in this species. These parasites are not evolving to infect any other primate because the Horsfield’s tarsier exists, but if that changes, we could all be the next target.
The International Union for Conservation of Nature lists the Horsfield’s tarsier as Vulnerable (IUCN, 2015), appearing on the IUCN Red List of Threatened Species.
Like other inhabitants of tropical forests, this species is threatened by habitat loss, with a significant portion of their forests being taken over for plantations, for logging, and under threat of wildfires. Another threat to their habitat is the exploitation of the Natuna gas fields off the Natuna Islands of Indonesia, particularly due to the emissions from the field.
Extensive use of pesticides and insecticides in agriculture indirectly affects Horsfield’s tarsiers by targeting their food sources. They are also caught for the illegal pet trade and hunted for bushmeat or because they’re perceived as pests, even though they’re not.
The Horsfield’s 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.
The Indonesian, Malaysian, and Bruneian governments came together to protect tropical forests in their shared territory, which is crucial to ensure the survival of the Horsfield’s tarsier. The species is also protected in both Indonesia and Malaysia.
Organizations like the Malaysian Primatological Society are also trying to educate the public about the harmful effects of the pet trade and why wild animals make for poor pets. However, there is far more that can be done.
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Written by Caroline Abraham, January 2024