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    Tarsiers
    By Ken Myron | November 27th 2010 09:43 PM | Print | E-mail | Track Comments
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    Anthropology by birth, cognitive ethology by grandiose pretense. I am a researcher specializing in prosimian behaviour, ethology, and the genetic...

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    § Suborder: Haplorrhini § Infraorder: Tarsiiformes § Family: Tarsiidae § Genus: Tarsius § Species: T. bancanus, T. dentatus, T. lariang, T. pelengensis, T. pumilus, T. sangirensis, T. syrichta, T. tarsier, T. tumpura § Subspecies: T. b. bancanus, T. b. borneanus, T. b. saltator
    Other names: T. bancanus: Horsfield's tarsier, western tarsier; tarsier de Bornéo (French); västligt spökdjur (Swedish); T. b. borneanus: Bornean tarsier; T. b. saltator: Belitung Island tarsier; T. dentatus: T. dianae, Dian's tarsier, Diana tarsier; T. lariang: Lariang tarsier; T. pelengensis: Peleng tarsier, Peleng Island tarsier; T. pumilus: Lesser spectral tarsier, pygmy tarsier, mountain tarsier; tarsero piemeno (Spanish); dvärgspökdjur (Swedish); T. sangirensis: Sagihe Island tarsier, Sangihe tarsier; T. syrichta: Philippine tarsier, Phillipine tarsier; tarsier des Philippines (French); filippinskt spökdjur (Swedish); T. tarsier: T. spectrum, Eastern tarsier, spectral tarsier, Sulawesi tarsier; tarsier des Célèbes (French); östligt spökdjur (Swedish); T. tumpara: Siau Island tarsier
    Life span: >16 years Total population: Unknown Regions: Brunei, Indonesia, Malaysia, Philippines Gestation: 157 to 193 days (5.2 to 6.3 months) Height: 9.7 cm to 13.2 cm (M&F) Weight: 57.5 to 153 g (M & F) Total population: Unknown Regions: Brunei, Indonesia, Malaysia, Philippines Gestation: 157 to 193 days (5.2 to 6.3 months) Height: 9.7 cm to 13.2 cm (M & F) Weight: 57.5 to 153 g (M & F)

    The taxonomy of the tarsiers is debated and some authors include more forms that are not included here. Groves (2005) recognizes 7 species of tarsier, with only T. bancanus separated at the subspecific level. I will follow Groves' taxonomy, which includes the recently described T. lariang as a full species (classified a subspecies until 2006).

    Very little is known about some of the tarsier species, especially T. pumilus, which had been known from only three museum specimens until the recent rediscovery of a wild population
    The taxonomy of the tarsiers is debated and some authors include more forms that are not included here. Groves (2005) recognizes 7 species of tarsier, with only T. bancanus separated at the subspecific level.

    I will follow Groves' taxonomy, which includes the recently described T. lariang as a full species (classified a subspecies until 2006). Very little is known about some of the tarsier species, especially T. pumilus, which had been known from only three museum specimens until the recent rediscovery of a wild population The taxonomy of the tarsiers is debated and some authors include more forms that are not included here.

    Groves (2005) recognizes 7 species of tarsier, with only T. bancanus separated at the subspecific level. I will follow Groves' taxonomy, which includes the recently described T. lariang as a full species (classified a subspecies until 2006). Very little is known about some of the tarsier species, especially T. pumilus, which had been known from only three museum specimens until the recent rediscovery of a wild population Very little is known about some of the tarsier species, especially T. pumilus, which had been known from only three museum specimens until the recent rediscovery of a wild population .

    Tarsier Morphology

    In general, tarsiers are among the smallest of the prosimians, and are relatively hard to distinguish from one another purely on differences in pelage; most of the pelage is grey with some, or some combination of, red, brown, yellow, or orange. There is often significant inter- and intra-specific overlap as well as variation in pelage by population and geographic location such that coloration is not a reliable indicator to distinguish all species from one another.

    There are some distinct differences between the species in coloration. T. tarsier for example, has white spots behind its ears and a scaly underside of the tail, traits which the other species do not possess. Among the species, the amount of tail hair is variable, decreasing from the hairiest tails found on the Sulawesi tarsiers (T. tarsier, T. pumilus, and T. dianae) to the intermediate T. bancanus, to the least hairy tail possessed by T. syrichta which is usually considered naked.


    Unique spinal morphology makes tarsiers capable of turning their heads nearly 180° in each direction, allowing them the ability to rotate their heads almost 360°. All tarsiers have claws on the second and third digits, two grooming claws on their feet, and pads on each of their fingers. Several bones of the heel (tarsals) are longer than those of any of the primates, and the genus name Tarsius partially describes this trait.

    Further, the amount of fur on the heel can be used to distinguish some tarsiers from one another. For example, while the heels of most tarsiers are fully furred, T. syrichta heels have very little, sparse, fine hair only, giving the appearance of being hairless in contrast to the rest of the body.

    Tarsiers move through their environment predominantly, but not exclusively, through leaping, which it is well adapted. In addition to the unique heel morphology, the legs and their muscles comprise around a quarter of the weight of the entire body. Due to these distinct features, tarsiers are capable of leaping quite far, with T. bancanus able to leap over 5m.

    Other forms of locomotion include bipedal and quadrupedal climbing, quadrupedal walking, clambering and hopping. The proportions of different locomotor activity differ with species however, and in some cases sets species apart from one another.

    The oldest living captive tarsier was over 16 years old when it died.
    Range
    Tarsiers are restricted to the Southeast Asian island nations of Brunei, Indonesia, Malaysia, and the Philippines, divided into two main geographic groups based on their morphology:
    Philippine-Western group T. syrichta is restricted to the Philippines; found on the southern islands of Bohol, Dinagat, Leyte, Mindanao, Samar, and Siargao T. bancanus stretches between and includes southern Sumatra and Borneo, including the islands of Bangka, Belitung and Karimata, as well as Serasan T. b. borneanus is found throughout the island of Borneo.
    Subspecifically T. b. bancanus is found on Sumatra, from the Musi River to the Sunda Strait)
    T. b. saltator is found on Belitung Island Eastern group East of Borneo, several species of tarsier call the island of Sulawesi home: T. dentatus (central Sulawesi) T. lariang (west-central Sulawesi) T. pumilus (restricted to the central Sulawesian montane mossy cloud forests) T. tarsier (Sulawesi and some surrounding islands) T. sangirensis ( restricted to the Greater Sangihe Island T. tumpara (found only on Siau Island) part of the Sangihe Island chainT. pelengensis (off of the east coast of Sulawesi) Population totals in the wild are unknown, however population density surveys have revealed tarsiers live in medium to low densities.

    The Siau Island tarsier is listed as one of the World's 25 Most Endangered Primates, and at most, likely numbers only one thousand or a few thousand. On mainland Sulawesi, a population density survey of spectral tarsiers sampled 156 individuals per square kilometer. T. dianae population density can reach 268 individuals per square kilometer in less disturbed habitat, but drops to 45 in habitats heavily disturbed by human activity. In the Philippines, T. syrichta lives at 57 individuals per square kilometer in fragmented forest T. pumilus is thought to live at an extremely low density (based on trapping rates).

    Habitat

    Tarsiers are found in a broad variety of habitats, including primary and secondary habitats, as well as certain habitats under human cultivation or use.

    Habitats in which tarsiers have been found include primary, secondary (secondary habitats in which tarsiers can be found include those which have been selectively and intensively logged; those containing coffee, nutmeg, coconut or coca plantations; areas being cut for bamboo and rattan extraction, and forests in which intensive or small-scale agricultural activities are taking place), mossy, microphyll, montane, bush, gallery, deciduous rain, and mangrove forests; thorn scrub, shrubland, swamps, riverine, palm, and bamboo habitats, seashore scrub, and even urban gardens, villages and grassland.

    Diet

    Tarsiers eat only prey and are the only entirely carnivorous primates, consuming no plant matter whatsoever. However, there are differences among the tarsiers in the types of animal matter that are consumed as well as seasonal changes in consumption.

    For example, T. bancanus eat arthropods mostly, including beetles, cockroaches, grasshoppers, butterflies, phasmids and cicadas. This species will also eat small birds, and other prey such as bats, frogs, freshwater crabs and snakes; T. tarsier has not been seen to eat birds, snakes, or other prey, but is the most insectivorous of the primates. Tarsiers are nocturnal.

    While not active during the day, if disturbed or threatened, tarsiers will leave their sleeping sites.
     
    T. bancanus usually awakes before sunset and does not retire for the night until after sunrise Tarsiers are most often found less than one or two meters (3.3 or 6.6 feet) above the ground. Potential predators of tarsiers include: civets, arboreal snakes, monitor lizards, raptors including owls, and feral cats.

    Social Organization And Behavior

    Variation in social system between species: T. tarsier social system may be monogamous with facultative polygyny, where one male's range overlaps with that of another female, and sometimes with multiple females whose ranges overlap T. lariang may also have a monogamous mating system (according to genetic evidence) Tarsiers outside of Sulawesi do not appear to have a monogamous social organization.

    T. bancanus and T. syrichta are characterized by a dispersed (noyau) mating system, where a male's range overlaps multiple female ranges.

    Spectral tarsiers decrease distances between group members during times of higher food resource availability and increased predation pressure T. dentatus increases distances between individuals in more disturbed habitats with fewer resources T. spectrum: considerably gregarious both in and out of the sleeping site, although outside the sleeping site group members usually are not in actual physical contact with one another (at sleeping sites, typical T. tarsier social behaviors include playing, allogrooming, snuggling, vocalizing, and scent-marking, while social behaviors with group members away from the sleeping site include playing, allogrooming, snuggling, vocalizing, scent-marking, food-sharing, and copulating)

    Group Size (the number of individuals who share a sleeping site) And Composition (varies between and within species) T. tarsier significant variation in group size and composition, the average group size is 3.1 individuals, comprised of at least a mated pair of adults but also sometimes with an additional adult female, and often offspring.

    Spectral tarsier groups do not contain more than one adult male Dian's tarsier groups usually consist of one adult male, one or more adult females, and their offspring sharing a sleeping tree T. bancanus do not sleep with other tarsiers and are usually found solitary T. syrichta are almost always alone as well.
     
    Territorial Behaviors

    Defense through patrolling and social encounters, as well as territorial advertisement through scent-marking and vocalizations.

    Territorial defense is seen in the spectral tarsier (T. tarsier) and likely functions most importantly in mate defense but also may have other functions as well.

    Territorial disputes in this species usually occur near the edges of a group's territory, and consist of group members aggregating, calling toward, chasing and lunging at the intruder T. bancanus males also patrol their territories In Sulawesi, vocalizations may function as territorial advertisement, where both males and females of T. tarsier, T. dentatus, and T. lariang perform morning duet vocalizations Both T. tarsier and T. syrichta mark territory by scenting home-range boundaries T. dentatus establishes sleeping sites near the periphery of home ranges, which may aid in the renewal of scentmarks along territorial boundaries.

    Reproduction The female sexual cycles of T. bancanus in captivity last on average 24 days. During estrus, the genitals of female T. bancanus swell and become reddish, a state that usually lasts for 6-9 days per cycle. ). In captivity, female T. bancanus solicit courtship by performing genital displays.

    Males then vocalize a "chirruping" call and sniff the genitals of the female. Both sexes may urinate. Courtship may last from 60 to 90 minutes but copulation itself lasts only around a minute and a half. Gestation in captive T. bancanus is around 178 days, females are capable of conceiving offspring at around two years of age. Copulation occurs on a vertical perch, with the male mounting the female in a dorsal-ventral position from behind and below. Post-copulation, the male will groom his genitals and the female will rub herself on various objects nearby.

    The sexual cycles of T. syrichta average 24.6 days Wild spectral tarsiers (T. tarsier), unlike other tarsiers, reproduce seasonally, with two observed mating seasons between April-June, and again between October-November and corresponding birth peaks between April-May and November-December. The average inter-birth interval in wild T. tarsier is 13.5 months. Estimated average gestation length in wild T. tarsier is 193 days (6.3 months). T. tarsier are sexually mature at around 518 days.

    PARENTAL CARE

    Relative to their parents, infant tarsiers are very large at birth (20-33% of adult weight) and are born with open eyes and fur Tarsier infants are born as singletons In captivity, T. bancanus birth weights average 23.0 g (0.8 oz) and T. syrichta birth weights average 23.2 g (0.8 oz) Wild infant spectral tarsiers T. tarsier are carried in the mouth of the mother in the manner of a cat and almost never by clinging to the fur, a pattern which is also seen in T. syrichta.

    In some captive observations of T. bancanus, mothers carried their offspring orally, in other studies this was not the case with mothers never carrying their offspring orally In the wild infant T. tarsier are carried about 20% the time overall, but carriage declines as the infant ages. The captive T. bancanus infant first moves away from its mother at 10-15 days old. Skilled locomotion commences in captive T. bancanus around 22-28 days old and mothers stop trying to carry their infant between 41 and 43 days old T. tarsier and T. bancanus infants are able to move quadrupedally before they are able to leap .

    In wild T. tarsier, the first leaps are seen at 32 days old Attempts to catch live prey in captive T. bancanus start at an average of 37 days old (Roberts 1994). However, in the wild, a T. tarsier infant was seen hunting at 26 days old (MacKinnon & MacKinnon 1980). Wild T. tarsier hunting success is first met at 45 days old Captive play in T. bancanus begins at an average of 22.5 days old. Between 38 and 49 days old, the mother and infant start to sleep apart, and completely cease to do so by 75 days old.

    Wild T. tarsier nursing conflict peaks in the 8-9th weeks of life and infants are weaned at an average of 80 days of age Weaning occurs at 80 days in T. bancanus and 82 days old in T syrichta. Perhaps the most interesting aspect of spectral tarsier (T. tarsier) infant rearing is the large amount of time the infant spends alone. While she forages, a wild mother will "park" her offspring and leave it by itself, occasionally visiting the infant.

    However, the T. tarsier mother usually stays relatively close to the "parked" infant and will "park" it at an average of 11 different times over the course of the. Until 70 days of age, T. tarsier infants are "parked" more than half of the time, usually almost 6 m (19.7 ft) above the ground and not in particularly concealed locations. Allocare is seen in wild spectral tarsiers (T. tarsier), and may be provided to the infant by subadults of both sexes and adult males with the most non-maternal allocare provided by subadult females (types of allocare that are seen include infant transport, food sharing, play, grooming, baby-sitting, physical contact, and increased vigilance and alarm calling.

    Communication



    There are noticeable differences in vocalizations between, and in some cases within tarsier species Wild tarsiers have shown that such differences are recognized by the tarsiers themselves.

    The implications of this are that groups that have different vocalizations or duet structure may in fact be different cryptic species and that there may be more species than are currently recognized Several species of Sulawesian tarsier (T. dentatus, T. tarsier, and T. lariang) duet at the end of their activity cycle, before sunrise near the sleeping site Vocal duets in T. tarsier occur regularly between mated pairs when they return to the sleeping tree, occurring roughly at the same time nearly every morning.

    Most duets are started by females and last several minutes There may be multiple functions of vocal duets, including territorial displays and mate guarding T. pumilus do not perform duets when returning to their sleeping site, and may vocalize rarely T. bancanus and T. syrichta do not perform duets In fact, wild T. bancanus are not very vocal at all at some study sites, while at others they are significantly so.

    T. bancanus has been reported to produce "calling concerts" in which several tarsiers call together, but such events are not analogous to the duets heard in other tarsiers (Crompton & Andau 1987).

    There are a number of types of vocalizations produced by tarsiers that are not part of duets. For example, T. tarsier has 15 different types of calls, including distress calls, alarm whistles, alarm calls, mid-intensity alarm calls, female screams, contact trills, contact whistles, food calls, play whistles, infant squeaks and other types of whistles T. bancanus use four general types of vocalization.
    Several postures in T. tarsier serve a communicatory function. Fear is communicated by folded ears while a crouched posture, an open mouth, and/or a lunge forward communicate a defensive threat. A bipedal stance with an open mouth is an aggressive threat .

    Tarsiers possess a gland in their lips as well as an abdominal gland, which, together with the anogenital region, function in olfactory communication when rubbed on substrates including other tarsiers.

    In fact, even if not seen or heard, tarsiers can be recognized as present in a given habitat purely by their scent marking alone. T. bancanus of both sexes scent-mark and vocalize most often during female estrus and proestrus .