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Horsfield's tarsier
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| Western tarsier[1] | |
|---|---|
| |
| C. bancanus in Borneo. Note the eyeshine. | |
Scientific classification 
| |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Primates |
| Suborder: | Haplorhini |
| Family: | Tarsiidae |
| Genus: | Cephalopachus Swainson, 1835 |
| Species: | C. bancanus
|
| Binomial name | |
| Cephalopachus bancanus (Horsfield, 1821)
| |
| |
| Western tarsier range | |
| Synonyms | |
Horsfield's tarsier (Cephalopachus bancanus) is the only species of tarsier in the genus Cephalopachus. Named by American naturalist Thomas Horsfield, it is also referred to as western tarsier. The species occurs on Borneo, Sumatra and nearby islands and is, like other members of the group, entirely nocturnal.
Taxonomy
[edit]Although Horsfield's tarsier was usually placed in the genus Tarsius with all other living tarsiers, it is quite distinct from the Philippine tarsier and the various tarsiers of Sulawesi and nearby islands; therefore, scientists have placed it in a separate genus, Cephalopachus.[4]
The taxonomy of this species is in doubt, with some subspecies considered unsure.[5] In fact, over 20 years few studies have been done on C. bancanus and a taxonomic revision based upon intensive and systematic field surveys is overdue. The IUCN believes that these subspecies should be treated as distinct and named as separate taxa until more definitive evidence is available.[6] When splitting the species into its own genus, Colin Groves and Myron Shekelle recognized the natunensis population as a distinct subspecies.[4]
There are four recognized subspecies of Horsfield's tarsier:
- Cephalopachus bancanus bancanus — Bangka Island tarsier
- Cephalopachus bancanus saltator — Belitung Island tarsier
- Cephalopachus bancanus borneanus — Bornean tarsier
- Cephalopachus bancanus natunensis — Natuna Islands tarsier
Habitat and distribution
[edit]Horsfield's tarsier is found in Southern Sumatra, Borneo and nearby islands.[7][page needed] The Bornean subspecies, C. b. borneanus, is known from many lowland sites in Sabah, Brunei, Sarawak and West Kalimantan and above 900 m (3,000 ft) in the Kelabit uplands in northern Sarawak. Other records show it from Kutai and Peleben in East Kalimantan and Tanjung Maruwe in Central Kalimantan.[7] This species can live in both primary and secondary forests, and it also lives in forests along the coasts or on the edge of plantations.[8]
Physical description
[edit]The pelage coloration ranges from pale-olive or reddish brown to pale or dark grey-brown, possibly varying with age. Based on 12 collected specimens,[7] the head to body measurement range from 121–154 mm (4.8–6.1 in). Horsfield's tarsier has an extremely long tail which can reach 181 to 224 mm (7.1 to 8.8 in) and is hairless except for tufts of hair at the end.[9] This species has two grooming claws on each foot. The fingers are very long and have pads on the tips. The toes have flattened nails except for the second and third toes on hind feet, which bear claw-like nails.[7] It has large eyes which do not reflect light.[inconsistent] The membranous ears are slender and almost bare. The molars of this species have high-cusps and are almost tritubercular.[10] The dental formula of Horsfield's tarsier is 2:1:3:3 on the upper jaw and 1:1:3:3 on the lower jaw.[11]
Biology
[edit]Horsfield's tarsiers are nocturnal, sleeping alone during the day in a tangle of vines or lianas at a height of 3.5 to 5 metres (11 to 16 ft).[12] This species prefers to sleep, rest, or remain stationary on perches that are angled 5 degrees from the vertical tree trunks, 1 to 4 cm (0.39 to 1.57 in) in diameter,[13] and it sleeps solitarily.[14] Before sunset, Horsfield's tarsier will wake up and wait 10 to 20 minutes before moving around the understory and spending 1.5 to 2 hours of the night foraging for food.[8] Horsfield's tarsier can be found from ground level up to a height of 7 m (23 ft) or more in the understory.[7]
This species is carnivorous. It mainly eats arthropods such as beetles, orthopterans like grasshoppers, katydids, and crickets, butterflies, moths, cockroaches, praying mantis, ants, phasmids, cicadas, dragonflies, freshwater crabs, and spiders,[8][15] but also will eat small vertebrates such as flying frogs,[15] bats (Chiroptera) including members of the genus Taphozous, the lesser short-nosed fruit bat (Cynopterus brachyotis), and the spotted-winged fruit bat (Balionycteris maculata), and snakes, of which venomous snakes have been found to be consumed, such as the elapid Calliophis intestinalis. This species was also found to consume birds, including spiderhunters, warblers, kingfishers, and pittas. It locates prey primarily by sound and catches the prey with its hands when foraging. Prey is killed through bites to the back of the neck[8] and the tarsier's eyes are shut when attacking.[16] It will consume the prey starting with the head and working its way down the body.[8] This species gets water both by drinking from a pool or stream, and by licking drops from bamboo leaves or from water running down the trunks of trees.[17] Horsfield's tarsier is a host of the acanthocephalan intestinal parasite Moniliformis tarsii.[18]
Like all tarsiers, Horsfield's tarsiers are vertical clingers and leapers, known for extraordinary leaping abilities. An individual will mainly support itself with its feet and the tail, both exerting enough force to hold the individual in place. The hands are not always used because of the pads located on the feet provide adequate grip. The hands are usually placed no higher than its nose except when resting; the hands are only placed higher up to maintain the position of the individual.[13] Other modes of locomotion used by the species include climbing, quadrupedal walking, hopping and "cantilevering."[12][15]
Life cycle
[edit]Horsfield's tarsiers are monogamous, with a copulation frequency during estrus of once per night.[19] Courtship calls are performed by the male and he emits 2–3 chirrups while opening and closing the mouth.[19] This call happens within 5 minutes of looking at the female. Once the male gives his courtship call, if the female is receptive, she will perform genital displays to him.[19] If the female is not in estrus, she will emit an agonistic call which is often followed by biting and pushing the male away.[19] Both sexes' calls last on average for 1 second, and the interval between calls is on average 3 seconds.[19]
Infants are born with their eyes open and fully furred and able to groom themselves.[20] The mother will carry her infant in her mouth and when she forages for food the mother will park the infant on a branch.[21] Infant sounds are mostly clicks: "k", "tk", "ki", or a rapid "kooih"[22] and can be heard when the infant is left alone or is cold.[22] The mother stays in contact with their infants using high-pitched calls. Infants were found to first use the tails as support during resting at 7–10 days.[20] Social grooming in this species only occurs between mothers and infants,[23] removing dead skin and parasites by scratching with their toe claws and licking their fur, avoiding their faces. Faces are cleaned by rubbing on branches and it is to reinforce social bonds.[23]
Young leave their mother's range at the onset of puberty, and find their own territory.[20] Horsfield's tarsiers mark their territory with scents from urine and glandular secretions on a substrate while scratching the surface with its hind-limb toe claws.[19]
Conservation status
[edit]
The rapid loss of habitat due to forest conversion, oil palm plantations, fire, and logging is cause for concern.[24] Additionally, the species is also collected for the illegal pet trade and wrongly considered a pest to agricultural crops. It can suffer, directly and indirectly, from the use of agricultural pesticides.
Horsfield's tarsier is listed as vulnerable in the 2008 IUCN Red List of Threatened Species,[2] listed in CITES Appendix II, and protected by law in Indonesia and in Malaysia.
In February 2007, the governments of Brunei, Malaysia, and Indonesia agreed to protect roughly 220,000 km2 (85,000 sq mi) of tropical forest in the "Heart of Borneo" region. Environmental group WWF was particularly active in the establishment of the protected area.[25] In the "Heart of Borneo" project, non-governmental organizations (NGOs) have played a role in promoting the critical initiative and in assisting the neighboring nations in its conceptualization, design, and implementation. The countries are to improve biodiversity conservation in Bornean production forests, and to ensure that such forests are not simply converted to agricultural land-uses such as oil-palm plantations after logging.[26]
Gallery
[edit]-
Cephalopachus bancanus bancanus from Bangka in National Museum of Ireland, Dublin -
Cephalopachus bancanus saltator from Belitung -
Cephalopachus bancanus borneanus -
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Postage stamp featuring the western tarsier and George VI (top left) -
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In darkness
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References
[edit]
- ^ Groves, C. P. (2005). Wilson, D. E.; Reeder, D. M. (eds.). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Baltimore: Johns Hopkins University Press. p. 127. ISBN 0-801-88221-4. OCLC 62265494.
- ^ a b Shekelle, M.; Yustian, I. (2020). "Cephalopachus bancanus". IUCN Red List of Threatened Species. 2020 e.T21488A17976989. doi:10.2305/IUCN.UK.2020-3.RLTS.T21488A17976989.en. Retrieved 13 November 2021.
- ^ Schlitter, D.A. (2005). Wilson, D.E.; Reeder, D.M. (eds.). Mammal Species of the World (4-th ed.). Baltimore, Maryland, USA: Johns Hopkins University Press. p. 127. ISBN 978-0-8018-8221-0.
- ^ a b Groves, C.; Shekelle, M. (2010). "The Genera and Species of Tarsiidae". International Journal of Primatology. 31 (6): 1071–1082. doi:10.1007/s10764-010-9443-1. S2CID 21220811.
- ^ Brandon-Jones, D.; Eudey, A.A.; Geissmann, T.; Groves, C.P.; Melnick D.J., Morales; J.C., Shekelle, M. & Stewart, C.B (2004). "Asian Primate Classification". International Journal of Primatology. 25 (1): 97–164. doi:10.1023/B:IJOP.0000014647.18720.32. S2CID 29045930.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Shekelle, M.; Yustian, I. (2021). "Cephalopachus bancanus ssp. bancanus". IUCN Red List of Threatened Species. 2021 e.T39762A17992163. doi:10.2305/IUCN.UK.2021-1.RLTS.T39762A17992163.en. Retrieved 13 November 2021.
- ^ a b c d e Payne, J.; Francis, C. M. & Phillipps, K (1994). A Field guide to the Mammals of Borneo. Petaling Jaya: The Sabah Society.
- ^ a b c d e Niemitz, C. (1979). "Outline of the behavior of Tarsius bancanus". In G.A. Doyle; R.D. Martin (eds.). The Study of Prosimian Behavior. New York: Academic Press.
- ^ Sussman, R.W (1999). Primate Ecology and Social Structure: Vol. 1 Lorises, Lemurs and Tarsiers. Pearson Custom Publishing.
- ^ Crompton, R.H.; Savage, R. & Spears, I.R (1998). "The mechanics of food reduction in Tarsius bancanus: Hard-object feeder, soft-object feeder or both?". Folia Primatologica. 69 (suppl 1): 41–59. doi:10.1159/000052698. PMID 9595687. S2CID 24464173.
- ^ Nowak, R.M (1999). Walker's Primates of the World. Baltimore: Johns Hopkins University Press. ISBN 0-8018-6251-5.
- ^ a b Crompton, R.H.; Andau, P.M (1986). "Locomotion and Habitat Utilization in Free-ranging Tarsius bancanus: A Preliminary Report". Primates. 27 (3): 337–355. doi:10.1007/BF02382075. S2CID 25836867.
- ^ a b Niemitz, C (1984a). "Locomotion and posture of Tarsius bancanus". In C. Niemitz (ed.). Biology of Tarsiers. Stuttgart: Gustav Fischer Verlag. ISBN 0-89574-182-2.
- ^ Crompton, R.H.; Andau, P.M (1987). "Ranging, activity rhythms, and sociality in free-ranging Tarsius bancanus: A preliminary report". International Journal of Primatology. 8 (1): 43–71. doi:10.1007/BF02737113. S2CID 39920648.
- ^ a b c Crompton, Robin Huw; Blanchard, Mary L.; Coward, Sam; Alexander, R. Mcneill; Thorpe, Susannah K. (2010). "Vertical Clinging and Leaping Revisited: Locomotion and Habitat Use in the Western Tarsier, Tarsius bancanus Explored Via Loglinear Modeling". International Journal of Primatology. 31 (6): 958–979. doi:10.1007/s10764-010-9420-8. Retrieved 21 November 2024.
- ^ Fogden, M.P.L (1974). "A preliminary field study of the western tarsier, Tarsius bancanus Horsefield". In R.D. Martin; G.A. Doyle; A.C. Walker (eds.). Prosimian Biology. Pittsburgh: University of Pittsburgh Press.
- ^ Niemitz, C (1984d). "Synecological relationships and feeding behaviour of the genus Tarsius". In C. Niemitz (ed.). Biology of Tarsiers. Stuttgart: Gustav Fischer Verlag. ISBN 0-89574-182-2.
- ^ Deveaux, Timothy P.; Schmidt, Gerald D.; Krishnasamy, M. (1988). "Two New Species of Moniliformis (Acanthocephala: Moniliformidae) from Malaysia". The Journal of Parasitology. 74 (2): 322–5. doi:10.2307/3282462. JSTOR 3282462. PMID 3128654.
- ^ a b c d e f Wright, P.C.; Toyama, L.M. & Simons, E.L (1986). "Courtship and Copulation in Tarsius bancanus". Folia Primatologica. 46 (3): 142–148. doi:10.1159/000156247. PMID 3100401.
- ^ a b c Roberts, M (1994). "Growth, development, and parental care in the Western tarsier (Tarsius bancanus) in captivity: Evidence for a "slow" life-history and nonmonogamous mating system". International Journal of Primatology. 15 (1): 1–28. doi:10.1007/BF02735232. S2CID 7462413.
- ^ Haring, D.M.; Wright, P.C. & Simons, E.L (1985). "Social behaviors of Tarsius syrichta and Tarsius bancanus". American Journal of Physical Anthropology. 66: 179. doi:10.1002/ajpa.1330660204.
- ^ a b Niemitz, C (1984b). "Vocal communication of two tarsier species (Tarsius bancanus and Tarsius spectrum)". In C. Niemitz (ed.). Biology of Tarsiers. Stuttgart: Gustav Fischer Verlag. ISBN 0-89574-182-2.
- ^ a b Niemitz, C (1984c). "An investigation and review of the territorial behaviour and social organisation of the genus Tarsius". In C. Niemitz (ed.). Biology of Tarsiers. Stuttgart: Gustav Fischer Verlag. ISBN 0-89574-182-2.
- ^ Yustian, I.; Merker, S. & Supriatna, J (2008). "RELATIVE POPULATION DENSITY OF Tarsius dianae IN MAN-INFLUENCED HABITATS". Asian Primates Journal. 1 (1).
- ^ Butler, R. A (2006). "Borneo". Retrieved January 27, 2009.
- ^ World Wildlife Fund. (2007). Resolution concerning the 'Heart of Borneo'. Association for Tropical Biology and Conservation.
Horsfield's tarsier
View on GrokipediaTaxonomy
Classification and phylogeny
Horsfield's tarsier is classified within the kingdom Animalia, phylum Chordata, class Mammalia, order Primates, suborder Haplorrhini, infraorder Tarsiiformes, and family Tarsiidae, the only extant family in its infraorder.[4][2] The species bears the binomial name Cephalopachus bancanus (Horsfield, 1821), though some classifications retain Tarsius bancanus; the genus Cephalopachus was resurrected in recent taxonomy to distinguish western tarsiers from eastern congeners based on cranial morphology, dental formula, and postcranial traits such as elongated tarsal bones.[5][1] Four subspecies are currently recognized, reflecting geographic variation across island populations: C. b. bancanus (southern Sumatra and nearby islands), C. b. borneanus (Borneo), C. b. saltator (Belitung and Bangka islands), and C. b. natunensis (Natuna Islands).[4][6] Phylogenetic analyses of complete mitochondrial genomes position the family Tarsiidae as the sister group to Anthropoidea (New World monkeys, Old World monkeys, and apes) within Haplorrhini, with the tarsier-anthropoid divergence estimated at 58–63 million years ago based on molecular clock calibrations.[7] Tarsiidae forms a monophyletic clade, distinct from strepsirrhine primates, supported by shared derived traits including dry noses, forward-facing eyes, and placentation patterns, though early debates on tarsier affinities arose from mosaic morphologies blending prosimian and simian features.[7][8] Within Tarsiidae, C. bancanus represents the western tarsier clade, genetically divergent from eastern (Sulawesi) and Philippine tarsiers; cytochrome b sequence data indicate a split between Bornean (C. b. borneanus) and Sulawesi lineages approximately 11 million years ago, consistent with vicariance events tied to Sundaland paleogeography.[9] This positions western tarsiers as a basal offshoot within the family, with limited hybridization across Wallace's Line.[9][10]Nomenclature and synonyms
Cephalopachus bancanus (Horsfield, 1821) is the currently accepted binomial nomenclature for Horsfield's tarsier, the sole species in the genus Cephalopachus, which was resurrected in modern taxonomy to distinguish it from Philippine tarsiers previously grouped under Tarsius.[5][2] The species was originally described as Tarsius bancanus by American naturalist Thomas Horsfield in 1821, based on specimens collected from Bangka Island (formerly Banca) in Indonesia, with the specific epithet "bancanus" derived from the type locality.[11][12] The vernacular name "Horsfield's tarsier" directly honors Horsfield for his description, while "western tarsier" reflects its distribution in western Indonesia and Borneo relative to eastern congeners.[12] The primary synonym is Tarsius bancanus Horsfield, 1821, reflecting its historical placement in the broader Tarsius genus before phylogenetic revisions emphasized morphological and vocalization differences warranting separation into Cephalopachus.[12][11] Subspecies nomenclature includes C. b. bancanus, C. b. borneanus, C. b. natunensis, and C. b. saltator, though some analyses suggest natunensis may synonymize with bancanus and others with borneanus due to cryptic variation and limited sampling.[2] No other junior synonyms are widely recognized at the species level in peer-reviewed taxonomic databases.[5]Physical description
Morphology and measurements
Horsfield's tarsier (Tarsius bancanus) possesses a compact body with disproportionately large eyes, elongated hind limbs adapted for vertical clinging and leaping, and a long, tufted tail for balance.[4] The head is rounded with forward-facing eyes that are larger in volume than the brain, enabling enhanced low-light vision, while the ears are thin and membranous for acute hearing.[13] The fur is dense and soft, typically grayish-brown dorsally and paler ventrally, providing camouflage in forested environments.[3] Elongated digits terminate in adhesive pads, facilitating grip on vertical surfaces, and the dental formula is 2/1, 1/1, 3/3, 3/3, suited for insectivory.[4] Sexual dimorphism is evident, with males generally larger than females in body size and hind limb length.[14] Head-body length ranges from 11.4 to 14.5 cm, with males averaging around 12 cm.[3][15] Tail length measures 20 to 23.5 cm, often exceeding the body length and bearing a terminal tuft of hairs.[15] Body weight varies from 100 to 139 g, with males typically 110-138 g and females 100-120 g.[2][16]| Measurement | Range (cm or g) | Notes |
|---|---|---|
| Head-body length | 11.4–14.5 cm | Males slightly longer than females[15][4] |
| Tail length | 20–23.5 cm | Tufted at tip[15] |
| Weight (males) | 110–139 g | Average ~128 g[13][2] |
| Weight (females) | 100–120 g | Average ~117 g[13][2] |
| Hind limb length (males) | ~71 mm | Significantly longer than in females[14] |
Sensory and anatomical adaptations
Horsfield's tarsier possesses oversized eyes, each larger than its brain, adapted for nocturnal vision with a retinal structure featuring high cone density for sharp central acuity despite low light conditions.[17] The eyes measure up to 16 mm in diameter and are immobile within the skull, but specialized upper cervical vertebrae enable head rotation of nearly 180 degrees in each direction, allowing a total visual sweep approaching 360 degrees.[4] Visual optics include a large cornea and a lens of 10 mm diameter and 6.5 mm thickness, optimizing light gathering in dim environments.[18] Auditory adaptations feature large, mobile, thin-walled ears sensitive to high-frequency sounds, aiding in the detection of insect prey movements and conspecific communication via ultrasonic vocalizations exceeding 10 kHz.[19] These ears, combined with neural specializations, support precise localization of cryptic prey during aerial captures.[17] Anatomically, elongated tarsal bones in the hindlimbs, comprising over twice the length of the forelimbs relative to body size, facilitate vertical clinging and leaping locomotion, with leaps spanning up to 5 meters.[4] Hands and feet exhibit long, slender digits tipped with adhesive pads for secure grasping of vertical supports, while the feet include specialized grooming claws on the second and third toes and unique bone rotations for inverted positioning during perching.[20][21]Distribution and habitat
Geographic range
Horsfield's tarsier (Tarsius bancanus) is endemic to Southeast Asia, with its range spanning the islands of Borneo and Sumatra, as well as several smaller adjacent islands including Bangka, Belitung, and Karimata.[4][3] The species occurs in Indonesia, Malaysia, and Brunei, primarily in lowland regions up to elevations of approximately 1,200 meters.[22] On Borneo, populations are documented across the Malaysian states of Sabah and Sarawak, the entirety of Brunei, and the Indonesian portion known as Kalimantan, covering an estimated area exceeding 100,000 km² for the Bornean subspecies T. b. borneanus.[14][1] In Sumatra, the distribution is concentrated in the southern lowlands.[3] Records from global biodiversity databases confirm occurrences in coastal and dipterocarp forest edges within these islands, though precise boundaries remain subject to ongoing surveys due to the species' nocturnal habits and dense habitat preferences.[2]Habitat requirements and microhabitats
Horsfield's tarsier (Tarsius bancanus) primarily inhabits lowland tropical rainforests across Borneo, Sumatra, Bangka, Belitung, and nearby islands, favoring primary and secondary forests with dense understory vegetation.[14] It also occupies peat swamp forests, mangroves, and forest edges, demonstrating tolerance for moderately disturbed habitats such as selectively logged areas and plantation understories where vertical supports persist.[23] These environments provide the structural complexity essential for its vertical clinging and leaping locomotion, with activity concentrated in the lower forest strata up to approximately 7 meters above ground.[4] Microhabitats selected by T. bancanus emphasize slender vertical substrates, including saplings, vines, and lianas with diameters at breast height (DBH) of 4 cm or less, which facilitate clinging, leaping between supports, and prey ambushes.[23] [24] Individuals supplement these with horizontal branches and angled trunks for resting and scanning, particularly in areas rich in insect prey near the ground.[25] Daytime sleeping sites consist of dense foliage tangles or hollows 3.5 to 5 meters off the forest floor, offering concealment from diurnal predators and thermal regulation in humid conditions.[4] Such microhabitat preferences underscore the species' reliance on undisturbed understory integrity, as canopy gaps from logging reduce suitable supports and increase exposure.[14]Behavior
Activity patterns and locomotion
Horsfield's tarsier (Cephalopachus bancanus) exhibits strictly nocturnal activity patterns, emerging from diurnal resting sites shortly after sunset and retreating before dawn, with peaks in movement and leaping occurring early and late in the night.[4][26] Individuals travel an average of 1,800 meters per night across home ranges spanning 4.5 to 11.25 hectares, primarily foraging and navigating in low-light conditions adapted to their large eyes and specialized vision.[27] Locomotion in Horsfield's tarsier is characterized by vertical clinging and leaping (VC&L), a specialization for arboreal environments where individuals cling to vertical supports such as tree trunks and leap horizontally between them, comprising the majority of travel.[25] Leaps are predominantly level rather than upward or downward, with average movement heights of 0.89 meters above ground, and ground travel limited to about 5% of activity.[27][3] This leaping capability enables horizontal distances of up to several meters per bound, facilitated by elongated hind limbs and adhesive pads on digits for grip on bark and foliage.[3][25] Occasional climbing and walking supplement leaping, particularly during initial emergence or when navigating dense understory vegetation.[27]Social structure and communication
Horsfield's tarsiers (Tarsius bancanus) exhibit a solitary but social organization, characterized by a noyau system in which adult males maintain home ranges overlapping with those of multiple females, while individuals forage and travel independently during their nocturnal activity. Territories are defended through vocal and olfactory signals, with occasional overlap allowing for mating opportunities without cohesive group foraging. Small roosting aggregations of 2–3 individuals, including unrelated adults or family members, occur sporadically, possibly for mutual predator vigilance or microclimate regulation in humid forest hollows.[29] Communication relies heavily on vocalizations, with mated pairs producing duet calls at dusk and dawn to coordinate activity onset/cessation, reinforce bonds, and advertise territories. Female-initiated whistles elicit male chirp responses in these duets, which may include ultrasonic frequencies beyond human hearing (e.g., peaks above 20 kHz in alarm and distress calls).[30] [31] Other calls encompass agonistic screams, contact squeaks for mate location, and whistles during courtship, supplemented by tactile cues like tail-grasping prior to copulation. Scent marking via urine and facial glands delineates ranges and conveys individual identity, minimizing direct confrontations in this dispersed system.[3][4]Foraging and hunting strategies
Horsfield's tarsiers (Tarsius bancanus) are strictly nocturnal and solitary foragers, employing a classic sit-and-wait or perch-hunting strategy adapted to their arboreal habitat.[1] Individuals perch vertically on tree trunks or branches in the forest understory, often at heights of 2–5 meters, remaining motionless for extended periods while scanning for prey.[32] This ambush approach conserves energy in their low-metabolic-rate physiology, allowing them to exploit the darkness with acute sensory adaptations.[4] Prey detection primarily relies on vision via oversized, independently rotatable eyes that provide stereoscopic acuity and sensitivity to low light, enabling localization of insects, small birds, lizards, and bats within dense foliage.[3] Audition supplements this through large, mobile ears that pinpoint rustling or wingbeats, though olfaction plays a minimal role in hunting.[3] Upon identifying a target, typically within 1–2 meters, the tarsier executes a rapid strike: either a stationary reach-and-grab with elongated fingers, a short lunge, or a powerful leap propelled by hind limbs capable of jumps up to 3 meters.[4] Captive observations of T. bancanus reveal three main capture techniques—immobile grabs, leaps, and pounces—with an overall success rate of 88%, underscoring the efficacy of their predatory morphology.[4] Hunting is invariably solitary, with no evidence of cooperative or group-based tactics; individuals forage independently throughout the night, covering home ranges of 1–2 hectares while vocalizing to maintain spacing.[32] This strategy aligns with their insectivorous specialization, targeting evasive arthropods that demand precision over pursuit, though occasional vertebrate prey may require bolder aerial intercepts.[1] Juveniles develop foraging proficiency rapidly, with locomotor and predatory behaviors maturing within weeks post-weaning to support independence.[33]
Ecology and life history
Diet and trophic role
Horsfield's tarsier (Cephalopachus bancanus) is entirely carnivorous, with its diet dominated by arthropods such as beetles, cockroaches, grasshoppers, butterflies, moths, praying mantises, ants, phasmids, and cicadas.[4][3] Occasionally, individuals consume small vertebrates including birds, bats, lizards, and snakes, though these constitute a minor portion of the overall intake.[4] Prey items are typically captured through leaps of up to 5.8 meters—approximately 45 times the tarsier's body length—and consumed whole, with high-cusped teeth facilitating the reduction of hard-bodied insects.[3][34] As a nocturnal insectivore, Horsfield's tarsier occupies a mid-trophic level in its forest ecosystem, functioning primarily as a predator that regulates arthropod populations, thereby influencing insect pest dynamics in habitats like jungle rubber agroforests.[1] Studies in Bangka Island, Indonesia, highlight the species' reliance on diverse insect communities, with beetle and orthopteran abundance correlating to suitable foraging grounds.[35] This predatory role extends to occasional vertebrate predation, potentially curbing small prey abundances, while the tarsier itself serves as prey for larger carnivores such as owls and snakes, embedding it within broader food web interactions.[36] Feeding behaviors, observed via field studies and videography, emphasize rapid mastication adapted to a varied animal diet, underscoring efficient energy acquisition in low-light environments.[37]Reproduction and development
Horsfield's tarsier females exhibit estrous cycles averaging 24.0 ± 3.2 days, characterized by external genital swelling lasting 6-9 days, during which copulation typically occurs on the first day of estrus.[38] Courtship precedes mating and lasts 1-2 hours, with males mounting females and performing 61-190 thrusts over 60-90 seconds, culminating in ejaculation regulated by the female.[39] Observations in captivity indicate a non-monogamous mating system, challenging prior assumptions of strict monogamy, as females may solicit multiple partners and males show tolerance toward extra-pair copulations.[4][40] Gestation lasts approximately 178 days, after which females give birth to a single offspring, which represents up to 25% of the mother's body weight.[41] Newborns are precocial, born fully furred with eyes open and capable of clinging to branches, though they lack locomotor independence for about four weeks and are "parked" in safe locations by the mother during foraging bouts.[3] Weaning occurs around 80 days post-birth, with infants relying on maternal transport and protection initially.[42] Postnatal growth is exceptionally slow relative to body size, with the rate to physical maturity among the lowest recorded for primates, reflecting a "slow" life-history strategy adapted to stable, low-predation environments.[33] Fetal development similarly proceeds at one of the slowest rates documented across mammals.[33] Sexual maturity is reached at approximately 2-2.5 years in females, enabling reproduction in a species with a lifespan exceeding 13 years in captivity.[43] Parental care is primarily maternal, with limited male involvement beyond mating, and captive breeding success hinges on social grouping strategies that mimic wild multimale-multifemale dynamics.[44]Predators and mortality factors
Horsfield's tarsiers face predation from nocturnal and arboreal species that exploit their forest habitat. Snakes, including climbing species, and arboreal mammals such as slow lorises (Nycticebus spp.) are primary threats, leveraging overlapping niches to access tarsiers during inactivity or feeding.[3] Monitor lizards (family Varanidae), including goannas, have been documented preying on individuals, capitalizing on ground-to-tree transitions.[29] Aerial predators like large owls and birds of prey, along with terrestrial carnivores such as wild cats, pose additional risks, particularly to juveniles or displaced adults.[29] Specific predation events remain underreported due to the species' elusive behavior, but observations confirm vulnerability to ambush by stealthy climbers.[29] Defensive adaptations include cryptic brown-grey pelage for camouflage and strict arboreality to evade ground predators, though these offer limited protection against specialized arboreal hunters.[3] Auditory dependence falters during mastication, heightening exposure.[3] Beyond predation, mortality factors are poorly quantified in the wild, with predation inferred as dominant given the species' longevity—estimated at 12 years—and low reproductive output.[3] Captive studies reveal elevated infant mortality from rearing challenges, potentially mirroring wild constraints like nutritional deficits or parental inexperience.[29] Disease and intraspecific conflict contribute minimally based on available data.[3]Conservation
Population status and IUCN assessment
Horsfield's tarsier (Cephalopachus bancanus) is assessed as Vulnerable on the IUCN Red List under criterion A2c, reflecting an inferred population reduction of at least 30% over the past three generations (approximately 20 years) primarily due to ongoing habitat loss from deforestation and land conversion.[14] The species' overall population trend is decreasing, driven by fragmentation and degradation of its lowland forest habitats across Borneo, Sumatra, and associated islands.[1] Global population size remains unquantified in primary assessments, as comprehensive surveys are lacking; however, local density estimates from field studies vary widely by habitat quality and location. In primary forests of Sarawak, densities reach up to 80 individuals per km², while in Sabah they average 15–20 per km², and in rehabilitated or secondary forests on Borneo, figures can drop to 28 per km² or lower in peat swamps (around 0.003 per km²).[45][14][23] These variations underscore the species' sensitivity to environmental degradation, with no evidence of recovery in impacted areas. The subspecies C. b. borneanus on Borneo faces similar pressures, with at least 30% habitat loss documented over recent decades.[14]