Trachypithecus johnii (Nilgiri langurs) are endemic to the southern portions of the Western Ghats, a mountain range in the south of India. They are found between 8°N and 12°N latitude and 76°E and 77.5°E longitude. (Malviya, et al., 2011; Ram, 2007)
Trachypithecus johnii typically inhabits a wide range of forest habitats in the Western Ghats. They are found primarily in secondary moist deciduous forests and wet evergreen to semi evergreen forests. They prefer locations that are as close to water, and as far away from humans, as possible.
Nilgiri langurs are an arboreal species, sleeping in the middle or lower canopy in trees of medium height. They reside in the sholas of the Western Ghats. Sholas are narrow stretches of forest surrounded by grasslands, nestled in valleys at high elevations. Nilgiri langurs live at elevations between around 300 and 2,500 meters, and are most commonly found at approximately 1,400 meters. (Malviya, et al., 2011; Poirier, 1969; Ram, 2007; Richardson, 2005)
Trachypithecus johnii is a colobine monkey. They share many of the characteristic colobine features, such as a complex stomach, a reduced thumb, and a long tail. Nilgiri langurs have a shiny black coat with a reddish-brown to gold head. Newborns are reddish-brown for up to ten weeks, when they gain the hue of the adults.
Similar to purple faced langurs, Nilgiri langurs have dark faces and white sideburns. Females have white patches on their thighs that distinguish them from males.
Nilgiri langurs are sexually dimorphic, with males slightly larger than females. The males of this species have a total body length that ranges between 78 to 80 cm, weighing between 9.1 and 14.8 kg. The females’ lengths range from 58 to 60 cm, weighing between 10.9 and 12 kg. The tails of both males and females vary in length between 68.5 and 96.5 cm. (Fleagle, 1999; Malviya, et al., 2011)
Trachypithecus johnii individuals are sexually dimorphic, with a male to female body size ratio of 1.2 to 1.0. This indicates modest intrasexual competition among males for female mates.
Though there is little documented information about the Nilgiri langur mating system, it is assumed to be similar to that of the Hanuman langur, to which it is closely related. Hanuman langurs exist in uni-male or multi-male groups. The frequency of uni-male groups is dependent on the ability of individual males to defend and retain groups of females. There are small numbers of females in these uni-male groups because larger numbers of females above a certain threshold are able to exert control over the number of males in their groups. Distance between groups, or population density, also has an effect on the proportion of uni-male to multi-male groups. When groups are more spread out, it is more advantageous for a male to remain in his current group than to risk predation while traveling alone to another group.
There is evidence that uni-male groups increase female birth rates, indicating that less male-male competition is better for the reproductive success of female langurs. (Grueter and Van Schaik, 2009; Srivastava and Dunbar, 1996)
There is a surge in birth rate for Nilgiri langurs at two points in the year: most notably in the months of May and June, and secondarily between September and November. This seasonality of breeding may reflect a regular seasonal depletion of resources, which would affect females' ability to ovulate and therefore conceive. This would indicate that Nilgiri langurs breed year-round, but only conceive when resources are plentiful. Nilgiri langurs typically have only one offspring at a time.
The length of the gestation period of Nilgiri langurs in the wild is not known, but is assumed to be comparable to the closely related Hanuman langur, the gestation period for which is 200 days. In captivity, the gestation period for Nilgiri langurs is between 140 and 220 days. At birth, infant Nilgiri langurs weigh on average 0.5 kg. ("Nilgiri langur", 2011; Koenig, et al., 1997; Malviya, et al., 2011; Richardson, 2005)
Although no data exist for Nilgiri langurs specifically, a recent study on the eruption of molars in Trachypithecus specimens indicated that the eruption of the third molar occurred between 3 and 5 years of age, indicating an individual had reached sexual maturity. (Ingicco, et al., 2012)
Trachypithecus johnii does not display strong bonds between mother and young compared to similar species, though nursing lasts almost a year. Occasionally, when young infants are in distress, their mothers will ignore the cries for help in an unusual display of apathy. One hypothesis explains this as a result of the relatively low threat of predators. In all other ways, however, Nilgiri langur mothers are attentive and nurturing. For example, offspring cling to their mothers’ bellies while moving and even jumping, and are also sheltered by their mothers during rainstorms.
When newborns are around 10 days old, their mothers will permit other females to handle and care for their young. This occurs when the mother wants to feed. One non-maternal female could 'baby-sit' the offspring of up to three mothers.
Infants are weened by the end of one year, and at that point are almost completely independent of their mothers. Until the end of their first year, Nilgiri langur infants spend the majority of their time with their mothers or with other close females, only rarely coming into contact with adult males. (Malviya, et al., 2011; Poirier, 1968)
There is no documented information on the lifespan of Nilgiri langurs in the wild, but they can live up to 29 years in captivity. ("Nilgiri langur", 2011)
Trachypithecus johnii is an arboreal and diurnal species. During peak activity, it engages alternatively in feeding and resting periods. There are a host of other social activities that are visible, primarily during resting periods. Examples of these are grooming, playing, chasing, watching, fighting, mounting, aggression, and dominance assertion.
Nilgiri langurs generally live in small female-centric groups. These groups can consist of one male and several females, several males and several females, or one or more solitary males. Typically, the uni-male, multi-female model is the most common. Group sizes have been documented between 1 and 27 members, with an average of 14 or 15 individuals. (Malviya, et al., 2011; Oates, et al., 1994; Poirier, 1970a)
Trachypithecus johnii exhibits subtle dominance hierarchies. There are two dominance structures within each group, one for males and one for females. Dominance structures are not completely rigid, in that dominance is expressed in the number of times a specific individual is forced to act subordinately to another. For example, an alpha female with higher status may act dominantly towards a beta female the large majority of the time, but would behave subordinately on rare occasions. However, a gamma female would usually behave subordinately towards a beta female, expressing dominance very infrequently.
Social status is more important for males than for females. The alpha female displays dominance mainly in choosing preferred feeding and sleeping sites. The alpha male displays dominance most noticeably in determining the traveling direction and timing of the entire group, but also in freedom of choice over daily life. The alpha male can eat with or socialize with any other member of the group.
Nilgiri langur males are typically more involved in dominance than females, though dominance behaviors in general are not particularly frequent. In addition, aggression during these encounters is avoided. There is little competition for food or mates, and subordinate individuals are careful to avoid potentially harmful situations. Nilgiri langurs therefore have a relatively relaxed daily life. (Poirier, 1970a)
Nilgiri langurs exhibit territorial behaviors when confronted by other groups of their species. This defense of territory directly involves only one adult male of each group. Males defend their home areas through physical displays, vocalizations, and chases. Confrontations sometimes escalate to physical violence, leaving both defending males and non-group males with scars on their faces and bodies. In extreme cases, male take-overs and infanticide are known to occur. Such territorial interactions usually take place in the areas where the home ranges of two or more groups overlap, though Nilgiri langurs usually avoid these overlap areas when the members of other groups are present. (Fleagle, 1999; Malviya, et al., 2011)
Trachypithecus johnii has an average home range of around 10,000 square meters. The size of the home range fluctuates with quality of habitat during the seasons: when preferred food is readily available, the range is smaller; when it is more scarce, the home range increases. The core area of this species includes feeding sites and resting or sleeping sites. These sites are chosen as close to water and as far away from humans as possible.
Nilgiri langurs communicate mainly through vocalization. Vocalizations have many different functions, with various calls related to different social situations. Vocal communications are observed during the maintenance of the social hierarchy, during territorial disputes, as a part of within-group female-female conflicts, and finally for male intervention into such conflicts.
Nilgiri langurs also communicate with olfactory, tactile, and visual signals. They are known to engage in mouth sniffing as a part of feeding. This species also exhibits numerous expressions to signal to other species members. Some examples of expressions include a threatening open mouth gesture, a submissive head shaking gesture, a friendly play invitation, and a comforting outstretched hand gesture directed from mothers towards infants. Instances of tactile communication involve biting, licking, embracing, stroking, and slapping. (Malviya, et al., 2011)
A folivorous species, Nilgiri langurs eat many kinds of leaves, which make up the majority of their diet. They also take in nutrients from fruits, seeds, nuts, stems, bark, flowers, and soil. The only carnivorous aspect of their diet is the occasional consumption of insects.
Nilgiri langurs prefer the leaves of teak trees, Tectona grandis, and consume these larger leaves more frequently than others that occasionally make up their diet.
Nilgiri langurs are reported to choose foods based on digestibility; they have a diet that is low in both fiber and vegetable tannin. It is hypothesized that they use the soil they consume as an antacid, which stabilizes the pH level of the stomach. (Horwich, 1972; Malviya, et al., 2011; Oates, et al., 1980)
Nilgiri langurs spend almost half of their waking hours feeding. When eating leaves, they first eat the tips, then they rip off the sides to expose the midrib, which they also consume. This is a delicate and deliberate process, with one side of each leaf pealed back at a time to expose the midrib of the leaf. Each leaf takes approximately 30 seconds to eat. During eating periods, in which Nilgiri langurs take and consume leaves almost continuously, about 5-10 seconds are taken between leaves. (Horwich, 1972; Malviya, et al., 2011)
Nilgiri langurs have vocalizations for distress, warning, and alarm, each with its own sound and significance. They emit high-pitched barks as alarm calls to nearby individuals, which can be either short in quick intervals or longer and continuous. The continuous alarm call usually represents a more pressing hazard. In response to hearing either of the barking alarm calls, Nilgiri langurs will display signs of fear often accompanied by flight.
Of all the primates endemic to the Western Ghats in India, Nilgiri langurs feed on the largest number of plant species. They consume over 115 different species, including at least 58 tree species, 6 shrubs, 13 non-woody plants, 32 vines, and 6 parasitic plants. Fruits, nuts, and seeds are also parts of their diverse diets, and they function in their ecosystem as seed dispersers. (Malviya, et al., 2011)
Trachypithecus johnii individuals are poached for various purposes. Their body parts are sold for use in traditional medicine and are even advertised as components of recipes for aphrodisiacs. In addition, they are hunted for their skins, which are used as drum heads. Nilgiri langurs are also captured and sold as pets. While these may be positive economic effects for humans, they have devastating negative consequences for the populations of Nilgiri langurs that remain in decline. (Malviya, et al., 2011; Singh, et al., 2008)
Nilgiri langurs are known as crop pests to cauliflower, potato, cardamom, and garden poppy farmers. However, this negative effect on humans may be exacerbated by the fact that people are constantly encroaching on the natural habitat of Nilgiri langurs by planting crops, mining, and building homes. (Malviya, et al., 2011; Singh, et al., 2008)
Only 50% of this species’ territory is within the protected area in the Western Ghats. Their population is estimated between 5,000 and 15,000 individuals and less than 10,000 mature individuals. The two main threats to Nilgiri langurs include the destruction of their natural habitat and poaching for various purposes.
Because of the relatively small number of mature adult Nilgiri langurs in the world, and because of the declining trend in population size, they are placed on the IUCN Red List as Vulnerable. In addition, they have been protected under the Indian Wildlife Protection Act since 1972. (Malviya, et al., 2011; Singh, et al., 2008)
There is evidence that the level of human disturbance, or habitat saturation, correlates positively with instances of infanticide in langurs. In effect, human disturbance lowers instances of female dispersal relative to male takeover. When males invade and take over a group, levels of infanticide are much higher than if females are able to more peacefully leave their previous groups, which only happens when langurs have not reached the holding capacity of their environment. This shows the negative effects of humans encroaching on the langurs' territory. (Sterck, 1998)
There is some debate over the classification of this species, giving rise to conflicting views on its taxonomic placement. Some taxonomists place Nilgiri langurs with Hanuman langurs, while others consider them a species of Trachypithecus. Still others place them in their own genus known as Kasi. Nilgiri langurs are therefore named Trachypithecus johnii, Semnopithecus johnii, Presbytis johnii, and Kasi johnii in various scientific literature.
This species' various common names include: black leaf monkey, hooded leaf monkey, Indian hooded leaf monkey, John's langur, Nilgiri black langur, and Nilgiri leaf monkey. (Fleagle, 1999; Richardson, 2005)
Claire Solomon (author), Yale University, Eric Sargis (editor), Yale University.
uses sound to communicate
Referring to an animal that lives in trees; tree-climbing.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).
ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates
a substance used for the diagnosis, cure, mitigation, treatment, or prevention of disease
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
parental care is carried out by females
an animal that mainly eats leaves.
A substance that provides both nutrients and energy to a living thing.
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
an animal that mainly eats fruit
an animal that mainly eats seeds
An animal that eats mainly plants or parts of plants.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
having the capacity to move from one place to another.
This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.
the area in which the animal is naturally found, the region in which it is endemic.
generally wanders from place to place, usually within a well-defined range.
found in the oriental region of the world. In other words, India and southeast Asia.
the business of buying and selling animals for people to keep in their homes as pets.
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
having more than one female as a mate at one time
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
Living on the ground.
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
breeding takes place throughout the year
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