Horsfield's Tarsier (Tarsius bancanus)
This nocturnal species has large eyes and large ears that are mobile. The molars of this species have high-cusps and are almost tritubercular (Crompton et al., 1998). This species has a dental formula of 2:1:3:3 on the upper jaw and 1:1:3:3 on the lower jaw (Nowak, 1999). The Horsfield's tarsier has a special adaptation in its neck vertebrae to help it turn its head 180 degrees. It needs to do this because its eyes can not move. This species lacks a tapetum lucidum found in many nocturnal animals. This species receives its name from the elongated tarsus bone. Horsfield's tarsier has two grooming claws on each foot. The tail of this species is naked, except for a tuft of hair at the end (Sussman, 1999). The pelage color of this species is ivory yellow in Sumatra and golden brown or rusty yellow in Borneo (Rowe, 1996). The average body mass for males is around 128 grams, and for females it is around 117 grams. Females have two pairs of mammae, one inguinal and one pectoral.
The Horsfield's tarsier is found in the following countries: Brunei, Indonesia, and Malaysia. The range extends from Borneo and the nearby islands of Karimata and Serasan, and southern Sumatra and the nearby islands of Bangka and Billiton (Nowak, 1999). 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 (Niemitz, 1979).
This species is a carnivorous species. The Horsfield's tarsier mainly eats insects, but also will eat small vertebrates. The insects consumed include: beetles, grasshoppers, cockroaches, butterflies, moths, praying mantis, ants, phasmids, and cicadas (Niemitz, 1979). This species will forage on the ground around clusters fruit, but not for the fruit itself rather the insects that are attracted by the fruit are the prey item (Fogden, 1974). Of the small vertebrates eaten are bats (Chiroptera) and snakes, of which poisonous snakes have been found to be consumed (Niemitz, 1979). For example the poisonous snake Manticora intestinalis was found to be hunted for by this species (Niemitz, 1979). The bat species consumed include: the horseshoe bat, Taphozus sp., the lesser short-nosed fruit bat, Cynopterus brachyotis, and the spotted-winged fruit bat, Balionycteris maculata (Niemitz, 1979). This species was also found to consume birds, including: spider-hunters, warblers, kingfishers, and pittas (Niemitz, 1979). At Sepilok, Borneo, it was found that scarabid beetles, orthopterans, and forest cockroaches formed the major part of the diet for Horsfield's tarsier (Jablonski and Crompton, 1994). This species locates prey primarily by sound and catches the prey with its hands when foraging (Niemitz, 1979). Frogs are another vertebrate prey eaten by this species (Crompton, 1987). Most prey items are killed with bites to the back of the neck (Niemitz, 1979). Also when this species attacks a prey item it will do it with the eyes shut (Fogden, 1974). When consuming prey Horsfield's tarsier will usually start with the head and work its way down the body (Niemitz, 1979). Jablonski and Crompton (1994) found that this species regularly forages at ground level. However, Roberts and Cunningham (1986) concluded that this species does not forage at ground level at all based upon observations. Infants were observed to forage at ground level for a short time (16 weeks) (Roberts and Cunningham, 1986). Roberts and Cunningham (1986) suggest that foraging exclusively in the understory and not at ground level or in the upper levels of forest may be adaptive to avoid predators. It has been suggested that this species occupies the ecological niche in the understory of the forests of Borneo that would be otherwise filled by owls (Strigiformes) but can not due to the dense undergrowth restricting the flight of owls (Niemitz, 1979).This species drinks by two different ways, one by drinking from a pool or steam, and two by licking water from bamboo leaves or from trunks of trees when water is running down the bark (Niemitz, 1984d).
This is a nocturnal species. Horsfield's tarsier sleeps alone during the day in a tangle of vines or creepers at a height of 3.5 to 5 meters (Crompton and Andau, 1986). This species prefers to sleep on perches that are angled 5 degrees from the vertical (Niemitz, 1984a). This species sleeps solitarily (Crompton and Andau, 1987). This species wakes up just before sunset, waits 10 to 20 minutes then begins moving around the understory (Niemitz, 1979). Usually this species will spend 2 to 1.5 hours of the night foraging for food (Niemitz, 1979). Horsfield's tarsier is found from ground level up to eight meters up in the understory (Fogden, 1974). Individuals move through the understory and forage solitarily, and males tend to move further during the night than females (Crompton and Andau, 1987). Males have larger home ranges than females, but females will secure home ranges at an earlier age than males (Fogden, 1974). Females home ranges are overlapped by one or more males (Crompton, 1987). Females home ranges were found not to overlap each other (Crompton and Andau, 1987). Home ranges for both sexes may be larger in primary forests as opposed to secondary forests (Niemitz, 1979).
The only predator of this species has been found to be feral cats (Felidae) (Niemitz, 1984d).
This species is a vertical clinger and leaper. Having the elongated tarsus helps them in leaping. Also the fibula and tibia is fused on the lower third part going towards the foot which also helps in leaping. This species will rest, sleep, or remain stationary on vertical tree trunks, 1 to 4 centimeters in diameter (Niemitz, 1984a). An individual will mainly support itself with its feet and tail, not having to use the hands as much because of the pads located on the feet and just below the tail exert enough force to hold the individual in place (Niemitz, 1984a). When resting the hands are usually placed no higher than the nose except when resting on thick diameter trees, on smooth surfaces, or when the tail is being used as support (Niemitz, 1984a). The hands being placed higher up assisted in maintaining the position of the individual (Niemitz, 1984a).
This species uses five main modes of locomotion:
- leaping: This is where the body is held upright and the hindlimbs make the first contact with the terminal support, and the hands are extended towards the support (Crompton and Andau, 1986). The tail is used in leaping to control the rotation of the body (Crompton and Andau, 1986). This is the most common mode of locomotion (Crompton and Andau, 1986).
- climbing: There are different types of climbing, first where the forelimbs are used more importantly (Crompton and Andau, 1986). Second is a bipedal type where the hindlimbs are used to thrust the individual upwards (Crompton and Andau, 1986). In climbing down an individual may do this by sliding or in a quadrumanous fashion (Crompton and Andau, 1986).
- quadrupedal walking: This is often slow and awkward with the limbs moving opposite to each other, that is first the left forelimb and right hindlimb then the right forelimb and left hindlimb (Crompton and Andau, 1986).
- hopping: There are two types of hopping, one where the forelimbs are not used when landing and the second type is where the forelimbs are used in landing (Crompton and Andau, 1986).
- "cantilevering": This is where an individual will extend its body only using its hindlimbs and the forelimbs are not in contact with anything (Crompton and Andau, 1986).
This species mainly moves amongst tree saplings in the forest (Crompton and Andau, 1986).
Monogamy for this species is suggested by that the frequency of copulation during estrus is only once per night (Wright et al., 1986a). However Crompton and Andau (1986) suggest that the Horsfield's tarsier has a mating system much like that of the nocturnal prosimians and Pongo pygmaeus where a male's home range overlaps those of one or more females' home ranges. This type of mating system is suggested by the pronounced estrus swellings of the female (Wright et al., 1986b). Also evidence for this type of mating system is suggested by the lack of parental care by males (Roberts, 1994). This species does not sleep and forage in its groups. The home ranges of females and males overlap, but females do not have home ranges that overlap with other females. Young Horsfield's tarsiers leave their range at the onset of puberty, and find their own territory. Males do not participate in the care of young, and females have been found to guard infants against males (Roberts, 1994). Social grooming in this species only occurs between mothers and infants (Niemitz, 1984c).
duets: this behavior is used to demarcate territories and functions in territorial defense.
courtship call: This is performed by the male and he emits 2-3 chirrups while opening and closing the mouth (Wright et al., 1986a). This call happens within 5 minutes of looking at the female (Wright et al., 1986a). The male does during courtship after the female will perform genital displays to him (Wright et al., 1986a). Each call lasts on average for 1 second and the interval between each call is on average 3 seconds (Wright et al., 1986a).
agonistic call: This call is emitted by the female and consists of harsh chatter noises (Wright et al., 1986a). This is done by the female when she is being sniffed at the genitals by the male and she is not in estrus and is often followed by biting and pushing the male away (Wright et al., 1986a). Each call lasts on average for 1 second and the interval between each call is on average 3 seconds (Wright et al., 1986a).
clicks: This call that is uttered by the infant sounds like "k", "tk", "ki", or a rapid "kooih" (Niemitz, 1984b). This call is heard when the infant is left alone or is cold (Niemitz, 1984b).
Olfactory communication is important for the Horsfield's tarsier. It is used to communicate territory demarcation, reproductive state, presence, and affiliation.
genital mark: This is where the female rubs her vulva against a substrate (i.e. a pole or vine), depositing vaginal or glandular secretions (Wright et al., 1986a). Females do this when they are in estrus, and the behavior is done to communicate the state of estrus to the male (Wright et al., 1986a). The duration of the behavior is on average 3 seconds (Wright et al., 1986a).
urine mark: This is performed by both sexes and this is where the individual will urinate on a substrate while scratching the surface with its hindlimb toe claws (Wright et al., 1986a).This is first done by the female as she is being sniffed by the male, the male then does this in return after the female (Wright et al., 1986a). The duration for the behavior is on average 5 seconds (Wright et al., 1986a).
scent mark with the epigastric gland: This marking behavior is used more by males than females in this species (Niemitz, 1979). This behavior is used to demarcate territories, and this has been observed to have been done on trees (Niemitz, 1984c).
scent mark with the circumoral gland: This marking behavior is most often done on another conspecific (Niemitz, 1979). This has been observed to be done on tree trunks (Niemitz, 1984c). Infants will also do this on their mothers.
genital inspection: This is done by the male and is where he will sniff and/or lick the female's genitalia (Wright et al., 1986a). The male does this to see whether the female is in estrus (Wright et al., 1986a). If the female is in estrus she will perform urine mark while he sniffs her genitals, but if she is not in estrus she will emit agonistic call (Wright et al., 1986a).
social grooming: This is when one individual grooms another, removing dead skin and parasites. This is used to reinforce social bonds, and this is only found to occur between mothers and infants in this species (Niemitz, 1984c).
This species gives birth to a single offspring once a year. The breeding season for this species is from October to December, and females give birth from January to February (Fogden, 1974). Roberts (1994), however, did not find any specific seasonality with regards to birth. It has been suggested that the insect food supply determines the breeding season in this species (Fogden, 1974). The estrus cycle of the female lasts from 24-25 days and there is no menstruation (Wright et al., 1986b). During courtship copulation will occur once during each night of estrus (Wright et al., 1986a). During estrus the labia minora of the female will enlarge and become pink, turgid, and shiny (Wright et al., 1986b). Females will solicit males when in estrus for copulations (Wright et al., 1986a). The gestation length for this species is 178 days (Izard et al., 1985). A long gestation period may relate to the dietary specialization of this species or the low metabolic rate (Izard et al., 1985).
After birth, the mother will carry her infant in her mouth and when she forages for food the mother will park the infant on a branch (Haring et al., 1985). Infants are born with their eyes open and fully furred and are able to groom themselves (Roberts, 1994). Infants were found to first use the tails as support during resting at 7-10 days (Roberts, 1994). Mother and infants begin to engage in play fighting when the infant is 20-25 days old (Roberts, 1994).
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Last Updated: April 17, 2007.
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