Purple-faced Langur (Trachypithecus vetulus)
This species has a sacculated stomach to assist in the breakdown of cellulose. The purple-faced langur has enlarged salivary glands to assist it in breaking down food. The dental formula of the purple-faced langur is 2:1:2:3 on both the upper and lower jaws (Ankel-Simons, 2000). Overall the pelage color of this species is brownish black on the body and limbs (Roonwal and Mohnot, 1977). Whiskers range in color from white to pale brown and are directed backward (Roonwal and Mohnot, 1977). Head and body length range from 44.7-67.3 centimeters and the tail length ranges from 58.9-85.1 centimeters (Roonwal and Mohnot, 1977). The newborn has a pelage color of pale gray with a brownish tinge on the chest, arms, and legs (Rudran, 1973b). The crown of the newborn is also pale gray with a brown tinge, but the occipital region is lighter (Rudran, 1973b). The naked parts of the newborn body are pink in color (Rudran, 1973b). This species has a relatively short thumb. The average body mass for an adult male purple-faced langur is around 8.5 kilograms, and for the female it is around 7.8 kilograms (Harvey et al., 1987).
This species has four subspecies each having differing pelage colorations:
- Trachypithecus vetulus vetulus: The overall coloration of this subspecies is gray-black with light-tipped hairs (Groves, 2001). The lumbar region, haunches, and the distal part of the tail are light brown with long creamy tips (Groves, 2001). The head and cheek whiskers are brown or gray-brown (Groves, 2001).
- Trachypithecus vetulus nestor: This subspecies is lighter and more gray-brown than Trachypithecus vetulus vetulus (Groves, 2001). The rump patch is silvery gray (Groves, 2001). The forearms and shanks are nearly black in color (Groves, 2001). The crown and nape are pale brown and the tail is slightly tufted at the tip (Groves, 2001).
- Trachypithecus vetulus philbricki: This subspecies is like Trachypithecus vetulus nestor except for having a less conspicuous rump patch (Groves, 2001). The lower parts of the limbs are black and the tail tip is pale, tawny to white, and not tufted (Groves, 2001).
- Trachypithecus vetulus monticola: This subspecies has very thick, brown pelage (Groves, 2001). The cheek whiskers are long and white, hiding the ears (Groves, 2001). The tail is short on this subspecies (Groves, 2001).
The purple-faced langur is found in the country of Sri Lanka. This species is found in monsoon scrub, mature secondary, semi-deciduous, and undisturbed cloud forests (Hladik, 1977; Rudran, 1973b; Hohmann, 1990).
This species has four subspecies each occupying differing ranges:
- Trachypithecus vetulus vetulus: This subspecies is found in the rainforests of southern Sri Lanka from south of the Kalu Ganga to Rama (Groves, 2001).
- Trachypithecus vetulus nestor: This subspecies is found from the north of the Kalu Ganga as far north as the rainforests (Groves, 2001).
- Trachypithecus vetulus philbricki: This subspecies is found in north and east Sri Lanka in the dry zone, up to 1,500 meters in East Matale and Madukelle Hills (Groves, 2001).
- Trachypithecus vetulus monticola: This subspecies is found in the mountains in altitudes from 1,200 to 2,000 meters (Groves, 2001).
The purple-faced langur is a folivorous species, but it will also consume fruit, flowers, and seeds (Hladik, 1977). This species prefers immature leaves to more mature ones because they are high in protein and low in lignin. At Polonnaruwa, the purple-faced langur spent 60% of feeding time on leaves, 12% on flowers, and 28% on fruits (Hladik, 1977). Two-thirds of leaves consumed were mature (Hladik, 1977). Most of the food eaten by this species came from twelve tree species: Adina cordifolia, Schleichera oleosa, Drypetes sepiaria, Alangium salvifolium, Elaeodendron glaucum, Grewia polygama, Syzygium cumini, Holoptelea integrifolia, Garcinia spicata, Walsura piscidia, Ficus spp., and Sapindus trifoliatus (Hladik, 1977). Adina cordifolia accounted for 40% of the diet at Polonnaruwa, with the leaves, flowers, and fruits eaten (Hladik, 1977). Schleichera oleosa and Drypetes sepiaria together accounted for 30% of the diet (Hladik, 1977). The subspecies Trachypithecus vetulus monticola was found to have a diet consisting of young leaves (75%), coriaceous leaves (16%), and flowers and fruits (10%) (Hladik and Hladik, 1972; cited in Hladik, 1977). Hladik (1977) found that the fruits the purple-faced langur preferred to eat tended to be fibrous and desiccated, whereas the sympatric hanuman langur, Semnopithecus entellus, preferred to eat fruits that were mature and fleshy. The diet of this species tends to be low in protein, 11.5% of the dry weight (Hladik, 1977). Hladik (1977) describes the diet strategy of the purple-faced langur as minimizing energy expenditure while sacrificing for a relatively low nutritional gain by being less mobile than the hanuman langur. This species has been observed to consume earth from termite mounds (Roonwal and Mohnot, 1977). Water is obtained by licking rainwater off leaves and branches and drinking water collected in tree cavities (Roonwal and Mohnot, 1977).
During the winter monsoon season (February to March) this species consumes a high amount of young leaves and shoots (Hladik, 1977). From May to June, this species increases its fruit consumption because fruits are now becoming more available, mainly consuming unripe fruits from species such as Elaedendron glaucum (Hladik, 1977). During the major dry season from July to September, this species will consume a large amount of flowers, mainly from Adina cordifolia (Hladik, 1977). When the next monsoon arrives (October to November), this species will eat mature leaves as well as young leaves and shoots that are available (Hladik, 1977). From December to January, leaves are an important part of the diet for the purple-faced langur (Hladik, 1977).
Group sizes range from 3 to 16 individuals (Manley, 1986). Rudran (1973b) found that average group sizes at Polonnaruwa were 8.4 individuals and at Horton Plains they were 8.9 individuals. This is a diurnal and an arboreal species, but will move on the ground where there is a lack of trees, only staying on the ground briefly (Roonwal and Mohnot, 1977). The home ranges of all-male groups overlap the home ranges of unimale groups, but unimale group home ranges will almost never overlap (Rudran, 1973a).
Predators of the purple-faced langur include humans, Homo sapiens, and leopards, Panthera pardus (Roonwal and Mohnot, 1977; Seidensticker, 1983).
The purple-faced langur moves through the forest quadrupedally (Fleagle, 1988; Ripley, 1967). Grand (1975) found that the purpled-faced langur moved twice as fast as compared to the toque macaque, Macaca sinica or the common langur, Semnopithecus entellus. This species can make spectacular drops of 50 or more feet when performing the great call sequence (Ripley, 1967). Ripley (1967) reports that this species is a better leaper than the common langur.
The purple-faced langur has a unimale social system, with a male having up to seven females in the harem (Manley, 1986; Rudran, 1973a). The basic group includes the resident adult male, one to seven adult females, and a number of subadults, juveniles and infants (Manley, 1986). Some groups may have two adult males (Rudran, 1973b). All-male groups exist, having numbers from 2 to 14 and having their own territories (Manley, 1986; Rudran, 1973a). In all-male groups, subadult and adult females may be present (Manley, 1986, 1978; Rudran, 1973a, b). In all-male groups, the females were found to be reproductively inactive due to infants and juveniles not being found (Rudran, 1973a). All-male groups will also split-up during the day, only to reform at the sleeping site (Rudran, 1973a). Rudran (1973a) also notes that in all-male groups membership tends to be flexible, where group members change periodically. All-male groups tend to occupy ecologically poorer home ranges than unimale groups (Rudran, 1973a). Manley (1986, 1978) makes note of a third type of social unit called 'wanderers', which are a mobile unit of males and females of around 1-3 individuals that tend to be shy and apprehensive. Wanderers are mostly adult and subadult males that have just left their natal group who are searching for females to build a harem (Manley, 1986). Wanderers can also be adult males that have been thrown out of their group during a take-over and one or two females followed them (Manley, 1986). Harems will gain and lose adult and subadult females over time (Manley, 1986). Females gained come from all-male groups and from wanderer groups (Manley, 1986). Males disperse from their natal group near the time of puberty.
This is a territorial species and the resident male will defend its territory aggressively against conspecific groups (Manley, 1986; Rudran, 1973a; Roonwal and Mohnot, 1977). Takeovers of the harem group by males from all-male groups have occurred (Manley, 1978, 1986). Harem males will spend part the day on watch for intruders to the home range, sitting in vantage points, such as the crown of emergent trees (Manley, 1986). Harem males will perform the great call sequence when another harem's male has been sighted, as a response to a similar call, and after evicting an intruder from the home range (Manley, 1986). Harem males will also attack other males and whole groups by chasing and even attacking individuals (Manley, 1986). Sometimes the intruder is killed in such attacks (Manley, 1986; Rudran, 1973a). The most come form of attacking is two males grappling each other and falling to the ground (Manley, 1986). Adult males will also harass members of its own group if they stray into another group's territory (Rudran, 1973a). Adult females will also join in on territorial defense with a reduced version of the territorial display (Manley, 1986). Adult females will behave aggressively towards other females by chasing and sometimes attacking them (Manley, 1986). All-male groups may trespass on to another territory to test the fitness of the resident male to see if a takeover is possible (Manley, 1986). Because of this territorial aggression, females have a difficult time trying join a harem (Manley, 1986). Females will approach the harem male slowly, then turn away not staring at the male and always keeping the back facing the male (Manley, 1986). This mimics sexual behavior and may reduce the aggression of the male and allow the female to join the harem (Manley, 1986). Females may also join a harem when there is a takeover of the harem by another male; the female would be no less foreign than the harem females (Manley, 1986).
Rudran (1973a) notes that the takeover and replacement of the harem male by an all-male group male is the mechanism by which unimale groups are maintained. Infanticide has been reported to occur during male takeovers of the group (Rudran, 1973a; Manley, 1978). Mothers will abandon injure infants after a takeover (Rudran, 1973a). Rudran (1973a) suggests that if mothers encourage independence of infants by rejecting them, then they would be less likely to be fatally injured during a takeover episode; evidence shows that in the purple-faced langur active rejection by the mother towards the infant does occur earlier than other primate species. Indifference by the mother towards the infant may help to promote self-reliance at an earlier age (Rudran, 1973a). Rudran (1973a) notes that the lack of subadults and juveniles he observed in the subspecies Trachypithecus vetulus vetulus is probably due to takeovers and the subsequent killing of infants. Although in the subspecies Trachypithecus vetulus monticola, replacements tend to occur at low frequency thus groups have more immature individuals (Rudran, 1973a). After unimale group replacement births occurred at regular intervals, signaling a synchrony of female sexual cycles (Rudran, 1973a).
Social play in the purple-faced langur includes: chasing, light wrestling, and swinging from branches (Rudran, 1973b). Infants begin social play from 12-20 weeks of age (Rudran, 1973b).
great call sequence: This is a territorial call emitted by the adult male of harem in response to the sighting of an intruder, a similar call, and after the eviction of intruders (Manley, 1986). This call can also be emitted spontaneously or as a response from loud noises (vehicles and airplanes) (Hohmann, 1990). Also during this behavior the performer will run vigorously, bounding through the trees and make exaggerated dropping leaps (Manley, 1986; Hohmann, 1990). Hohmann (1990) found that this call is composed of three basic patterns (one phrase) (in order): a biphasic harsh bark, two whoop units that each consist of a tonal exhalation phase and a non-tonal inhalation phase, and a monophasic snort. The interval is relatively long (mean of 0.979 seconds) between the whoop units and the monophasic snort (Hohmann, 1990). The whoop has harmonic frequency bands that range between 0.2 and 7.8 kilohertz (Hohmann, 1990). The monophasic snort has a band width between 2.5 and 7.6 kilohertz (Hohmann, 1990). The harsh bark has a mean band width of 8.5 kilohertz (Hohmann, 1990). The number of phrases that occur in a bout of calling range from 1 to 5, and the mean number of units in a bout was found to be 19.47 (Hohmann, 1990). Hohmann (1990) found there was a peak time for performing this behavior between 05.00 to 09.30 am. The strongest stimuli for the emission of this call was found to be similar calls from other adult males (Hohmann, 1990). This behavior resembles the whoop display of the Nilgiri langur, Trachypithecus johnii (Hohmann, 1990).
hooh call: This is described as a full, deep, throaty call given by adult males in the early morning (Roonwal and Mohnot, 1977).
shrill squeak: This is emitted by individuals when they are curious (Roonwal and Mohnot, 1977).
twitter: This call is birdlike in nature and is emitted when an individual is expressing pleasure or excitement (Roonwal and Mohnot, 1977).
infant whine: This is a high-pitched call emitted by the infant when distressed (Rudran, 1973b).
genital sniffing: This is done by the adult male, and is where he will sniff the genital region of the female to see if she is in estrus.
social grooming: This is when one individual grooms another and is used to reinforce the bonds between individuals.
The purple-faced langur gives birth to a single offspring. At Polonnaruwa a mating season may exist from October to January, which coincides with the beginning of the peak period of rainfall, food abundance, and declining temperatures (Rudran, 1973b). A birth between May and August does exist at Polonnaruwa (Rudran, 1973b). At Horton Plains a distinct birth peak was not found, but some groups showed birth synchrony (Rudran, 1973b). At Horton Plains a birth peak may not be found because of high food availability and rainfall throughout the year (Rudran, 1973b). At Polonnaruwa the interbirth interval was found to be around 22-25 months (Rudran, 1973b). The gestation period ranges from 195 to 210 days (Harvey et al., 1987).
At Polonnaruwa, Rudran (1973b) found that adult females will initiate sexual behavior by first head-shaking, then presenting to the adult male. The male will mount the female and then begin copulatory thrusts (Rudran, 1973b).
head-shaking: This is where the female shakes her head back and forth before she presents to the male.
presenting: This behavior is performed by the female to elicit a copulation from the male; this pattern tells the male that she is ready for copulation (Estes, 1991). Head-shaking precedes this display.
By 12-16 weeks the infant resembles the adult pelage coloration, but not fully until 28 weeks (Rudran, 1973b). From 12-20 weeks the infants becomes more independent of the mother and also begins to engage in social play (Rudran, 1973b). At 12-20 months the infant also begin to eat solid food, which at Polonnaruwa coincides with a period of food abundance (Rudran, 1973b). After 28 weeks, young are completely reliant on solid food and move independently, except in situations of danger when the mother will transport the young to safety (Rudran, 1973b). Weaning occurs at 7-8 months of age Females reach adulthood at 3.5 to 4 years of age (Jay, 1965; cited in Rudran, 1973b). Males tend to ignore infants (Roonwal and Mohnot, 1977).
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Last Updated: June 20, 2007.
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