SPECTRAL TARSIERS

spectral tarsier

Spectral tarsiers (Spectral tarsiers) live on several Indonesian islands including Sulawesi, Pulau Peleng, and Pulau Selajar. The greatest numbers of them are found in the northern peninsula of Sulawesi Island. They are found in primary rainforests but prefer secondary growth forests, perhaps because they can more of the food items they like there. Their main habitats are lowland evergreen rainforest near sea level, mangroves, scrub forests and lower montane rainforest up to 1500 meters (4920 feet). It is estimated their average lifespan in the wild is at least 10 years. [Source:Kenzie Mogk, Animal Diversity Web (ADW) /=]

Spectral tarsiers feeds exclusively on live animals, mainly insects with a preference for flying insects such as moths, locusts, beetles and cicadas. They occasionally eat small vertebrates, such as lizards or bats. According to Animal Diversity Web: Spectral tarsiers listen with their independently moving ears to locate potential prey. Once a prey item is targeted, a tarsier ambushes its prey with a sudden lunge, grasps it with its long, slender fingers, and bites to kill it. The tarsier then returns to its perch to consume its prey. This form of ambush hunting requires excellent hand-eye coordination. Spectral tarsiers can collect their prey out of the air, on the ground, or off leaves and branches. Tarsiers can eat 10 percent of their own body weight every 24 hours, and they drink water several times throughout the night. Spectral tarsiers appear to take advantage of the moonlight when foraging. This is an unusual behavior, as most small, nocturnal (active at night), mammals exhibit lunar phobia as a predator avoidance mechanism. Tarsiers cope with this increased risk of predation by foraging in groups.

Spectral tarsiers currently have plentiful numbers on Sulawesi, particularly in the northern peninsula, where densities of the animal rangw from 156 to 800 individuals per square kilometer. On the International Union for Conservation of Nature (IUCN) Red List they are listed as Vulnerable. In CITES (Convention on International Trade in Endangered Species of Wild) they are in Appendix II, which lists species not necessarily threatened with extinction now but that may become so unless trade is closely controlled. Their main threat is logging and habitat destruction which disturbes their preferred sleeping sites in places like strangler fig trees. Strangler figs are removed from human-utilized forests because they are seen as a threat to other commercially valuable trees. Their main known natural predators are arboreal are snakes, civets, monitor lizards, owls, raptors and feral cats.

Spectral Tarsier Characteristics

Spectral tarsiers have a small, round body covered in soft, velvety fur varying in color from gray to buff-gray. They have long scaly tails with tufts of fur on last third of the tail. They range in weight from 102 to 130 grams (3.6 to 4.6 ounces) and their head and body length ranges from 9.5 to 14 centimeters (3.7 to 5.5 inches). Their tail length ranges from 20 to 26 centimeters. Total length ranges from 29.5 to 40 centimeters. Sexual Dimorphism (differences between males and females) is present: Males are larger than females. Males weight 118 to 130 grams while females weigh 102 to 114 grams. [Source: Kenzie Mogk, Animal Diversity Web (ADW) /=]

range of the spectral tarsier

Spectral tarsiers are thought to be the most primitive tarsiers, as they lack disks on the ends of their fingers. According to Animal Diversity Web (ADW): They have long legs that are specialized for their saltatory form of locomotion; they can jump more than 40 times the length of their body. The tibia and fibula are fused together and act as a shock absorber when the animal jumps from tree to tree. The hindlimbs of tarsiers are twice as long as their head-body length. The femur, the bones of the lower leg (the fused tibia and fibula), and the bones of the foot are each roughly equal in length. The third finger of Spectral tarsiers is extremely long and slender and is only 15 percent shorter than the humerus. This trait is not symmetrically reproduced from the anterior to the posterior, as the fourth digit is the longest of the hindlimb digits. The second and third digits of the hindlimb are equipped with specialized toilet claws. /=\

The eyes of spectral tarsiers are immobile due to their large size, but this is compensated for by the ability to rotate the head 180 degrees. The ears of spectral tarsiers are thin and membranous and are able to move independently. Tarsiers possess sharp, heterodont teeth and quadrate molars. The dental formula of tarsiers is: I2/1, C1/1, P3/3, M3/3 = 34. Spectral tarsiers have a low basal metabolic rate and a low body temperature. They do not exhibit torpor, yet brown adipose tissue can be found in adults within the interscapular area; this is likely a retained paedomorphic trait. /=\

Spectral Tarsier Behavior

Spectral tarsiers are arboreal (live mainly in trees), scansorial (able to or good at climbing), saltatorial nocturnal (active at night), crepuscular (active at dawn and dusk), motile (move around as opposed to being stationary), territorial (defend an area within the home range) and social (associates with others of its species; forms social groups). The average territory size for males is three hectares; for female it is two hectares. Individuals are loyal to their sleeping site, often remaining there for multiple years, usually with a mate. Females often establish a territory adjacent to their parental territory, while males disperse twice as far as females. Spectral tarsiers scent-mark their territories with urine and secretions from their epigastric glands. They can be very territorial, engaging in altercations with neighboring groups if they venture into their boundaries. [Source: Kenzie Mogk, Animal Diversity Web (ADW) /=]

Spectral tarsiers are very active throughout the night. Kenzie Mogk, Animal Diversity Web At dusk, they travel for about 30 minutes until they find a forage site. During this time, they frequently stop to groom themselves by licking and scratching their fur with their toilet claws. If a heavy rain occurs, tarsiers find a dry area and remain inactive. They move through the trees and can leap more than 40 times the length of their body. As morning approaches, spectral tarsiers "sing" as they return to their sleeping sites, either as a duet with their mate or in a family chorus. These songs signal to neighboring groups that a territory is occupied.

Spectral tarsiers usually live in pairs or small family groups. They are highly social animals. When two adult group members are in physical contact, they spend all of their time resting and socializing. When less than 10 meters apart, they forage and, when they are 50 to 100 meters apart, they spend most of their time traveling. Spectral tarsiers also engage in play behavior, snuggling, allogrooming, and food sharing. Competition for food results in increased time foraging. Individuals appear to benefit from group living, particularly when predation pressure is high, when females are sexually receptive, and when there is high likelihood of encountering a potentially infanticidal male.

If a predator, particularly a snake, is identified, they emit an alarm call. This initiates mobbing behavior, in which numerous tarsiers gather and approach the predator as a group, screaming, lunging, and even biting. Mob groups usually consist of adult males from neighboring groups, which is interesting as most spectral tarsier social groups only contain one territorial (defend an area within the home range), adult male. This grouping by neighboring males suggests some form of cooperation among males during predator mobbing. If spectral tarsiers spot a bird of prey such as an owl, they sound an alarm call and participate in avoidance mechanisms such as moving further away from the predator and increasing cryptic behaviors.

Spectral Tarsier Senses and Communication

two spectral tarsiers leaping to catch an insect

Spectral sense and communicate using vision, touch, sound and chemicals usually detected with smell and communicate with duets (joint displays, usually between mates, and usually with highly-coordinated sounds), choruses (joint displays, usually with sounds, by individuals of the same or different species) and scent marks produced by special glands and placed so others can smell and taste them.[Source: Kenzie Mogk, Animal Diversity Web (ADW) /=]

Among the Species-specific vocalizations of spectral tarsiers are trills and twitters, alarm calls, duet songs, and family choruses. According to Animal Diversity Web Twitters and trills are used to converse or to make their location known to other group members while foraging. Alarms calls serve as a warning system to others when a predator is spotted and also encourage predator mobbing. Duet songs and family choruses convey territoriality and function as a mate guarding mechanism. As morning approaches, the female of the duet pair initiates a song once she has returned to the family’s sleeping site. The male and female sing very different but equally high-pitched songs, which can be heard up to 100 meters away. Species-specific vocal acoustics are used in conjunction with morphogenetics to assess classification of tarsiers. /=\

Spectral tarsiers use their urine as well as secretions from the epigastric gland, ano-genital gland, and circum-oral gland to mark the boundaries of their territory. Males scent mark twice as frequently as females. Physical contact appears to contribute to tarsier sociality, and members of the same group often rest and socialize while touching. Spectral tarsiers sit next to one another and intertwine tails and are know to snuggle. Visual communication appears to be most effective when group members are in close contact with one another. They communicate by changes in facial musculature and body posture. Folded ears seem to convey uneasiness, and a crouched posture is taken when defensive. When aggressive, a tarsier stands on its hind feet with its mouth open.

Spectral Tarsier Mating, Reproduction and Offspring

Spectral tarsiers are monogamous (have one mate at a time) and polygynous (males have more than one female as a mate at one time). They engage in seasonal breeding, breeding twice a year, with copulation occurring during either May or November. Females possess a bicornuate uterus and haemochorial placenta. The average number of offspring is one. The average gestation period is six months. The weaning age ranges from 21 to 80 days, with the time to independence ranging from four to 12 weeks. On average males and females reach sexual or reproductive maturity at age 17 months. [Source:Kenzie Mogk, Animal Diversity Web (ADW) /=]

Most of tarsiers are monogamous but spectral tarsiers may practice facultative monogamy or polygyny. Kenzie Mogk wrote in Animal Diversity Web: Monogamy appears to be the prevalent mating system in this species due to limited numbers of high-quality sleeping sites. Each individual female requires a high-quality sleeping site for herself and her young. Fig trees with large diameters are preferred but rare, which generally leads males and females to share sleeping sites and thus to form monogamous pairs. /=\

Polygynous groups occur 19 percent of the time. Monogamous groups often consist of two or three females with one reproducing female and one territorial (defend an area within the home range), male, while polygynous groups consist of six or more individuals with multiple reproducing females and a single male. The presence of large testes in Spectral tarsiers suggests that polygyny is fairly common, as large testes have been related to promiscuous mating systems. /=\

Offspring are born fully furred and with their eyes open. Newborns are precocial and are able to climb at just one day of age. Among mammals, tarsier offspring are the largest relative to the mother's body mass. Newborns weigh on average 23.7 grams, nearly 22 percent of the mother's body mass. A large proportion their weight is invested in the brain mass, eyes, and cranium. /=\ Lactation generally lasts up to 80 days. Independence occurs directly after weaning as offspring are capable of hunting on their own.

Young spectral tarsiers are precocial and receive only maternal care. Mothers pick up and carry their infants by mouth for the first three weeks and cache them trees while they forage. Offspring are left alone for an average of 27 minutes at a time, and then they are moved to new locations. Mothers generally remain within four meters of their young when foraging. Caching young in trees reduces the energetic cost of foraging, as carrying offspring is costly and offspring can weigh up to one third of the mother’s weight. Mothers sling offspring older than three weeks of age under their bellies while leaping and moving from tree to tree.

Image Sources: Wikimedia Commons

Text Sources: Animal Diversity Web animaldiversity.org ; National Geographic, Live Science, Natural History magazine, David Attenborough books, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Discover magazine, The New Yorker, Time, Reuters, Associated Press, AFP, Lonely Planet Guides, Wikipedia, The Guardian, Top Secret Animal Attack Files website and various books and other publications.

Last updated December 2024