Gray langur Alpha male langur Scientific classification Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Primates Family: Cercopithecidae Subfamily: Colobinae Genus: Semnopithecus
Type species Simia entellus
Species Rough distribution of the genus
Gray langurs or Hanuman langurs, the most widespread langurs of South Asia, are a group of Old World monkeys constituting the entirety of the genus Semnopithecus. All taxa have traditionally been placed in the single species Semnopithecus entellus. In 2001, it was recommended that several distinctive former subspecies should be given full species status, so that seven species are recognized. A taxonomic classification with fewer species has also been proposed. Genetic evidence suggests that the Nilgiri langur and purple-faced langur, which usually are placed in the genus Trachypithecus, actually belong in Semnopithecus.
Gray langurs are large and fairly terrestrial, inhabiting forest, open lightly wooded habitats, and urban areas on the Indian subcontinent. Most species are found at low to moderate altitudes, but the Nepal gray langur and Kashmir gray langur occur up to 4,000 metres (13,000 ft) in the Himalayas.
"Hanuman" refers to the Hindu deity Hanuman.
These langurs are largely gray (some more yellowish), with a black face and ears. Externally the various species mainly differ in the darkness of the hands and feet, the overall color and the presence or absence of a crest. There are also significant variations in the size depending on the species, but the head-and-body length of males is typically up to 75 cm (30 in) and that of females is 65 cm (26 in). Their tail is always longer than their body. Langurs from the southern part of their range are smaller than those from the north. At 26.5 kg (58 lb), the heaviest langur ever recorded was a male Nepal gray langur.
Langurs mostly walk quadrupedally and spend half their time on and the ground and the other half in the trees. They will also make bipedal hops, climbing and descending supports with the body upright, and leaps.  Langurs can leap 3.7-4.6 m (12.0-15.0 ft) horizontally and 10.7-12.2 m (35-40 ft) in descending.
Traditionally, only Semnopithecus entellus was recognized as a species, the remainder all being treated as subspecies. In 2001, it was proposed that seven species should be recognized, with the majority considered monotypic. This was followed in Mammal Species of the World in 2005, though several of the seven species intergrade, and alternative treatments exist where only two species (a northern and a southern) are recognized. Phylogenetic evidence supports at least three species (a north Indian, a south Indian and a Sri Lankan species). It has also been suggested that Semnopithecus priam thersites is worthy of treatment as a species rather than a subspecies, but at present this is based on limited evidence.
It has been suggested that Trachypithecus should be considered only a subgenus of Semnopithecus. If maintaining the two as separate monophyletic genera, the purple-faced langur and Nilgiri langur belong in Semnopithecus instead of the usual Trachypithecus. At present it is unclear where the T. pileatus species group (consisting of the capped langur, Shortridge's langur and Gee's golden langur) belongs, as available mtDNA data place it in Semnopithecus, while Y chromosome data place it in Trachypithecus.
The seven species of Semnopithecus recognized in Mammal Species of the World are:
- Nepal gray langur Semnopithecus schistaceus
- Kashmir gray langur Semnopithecus ajax
- Tarai gray langur Semnopithecus hector
- Northern plains gray langur Semnopithecus entellus
- Black-footed gray langur Semnopithecus hypoleucos
- Southern plains gray langur Semnopithecus dussumieri
- Tufted gray langur Semnopithecus priam
Distribution and habitat
Gray langurs can adapt to a variety of habitats. They inhabit arid habitats such as desert areas, dry open scrub, dry deciduous forests, but also tropical and subtropical evergreen rainforests, moist deciduous forest, broadleaf forest, subtropical pine forest, riverine forest, open park woods, mountain foothills, mountain forests, Himalayan oak-coniferous forests, temperate coniferous forest, sub-alpine forest, grasslands, meadows, scrub, scrub forests, and mixed grasslands. They live at altitudes up to 4,000 m (13,000 ft) including areas that receive snowfall in the winter. They can adapt well to human settlements, and are found in villages, towns, residential areas, tourist areas, temple grounds, orchards and cultivated areas. They live in densely populated cities like Jodhpur, which has over a million inhabitants.
Ecology and behavior
Gray langurs are diurnal. They sleep during the night in trees or hunting towers or high-tension electric poles when in human settlements. When resting in trees, they generally prefer the highest branches.
Gray langurs are primarily herbivores. However, unlike some other colobines they do not exclusively eat leaves and leaf buds of herbs, but also coniferous needles and cones, fruits and fruit buds, evergreen petioles, shoots and roots, seeds, grass, bamboo, fern rhizomes, mosses, and lichens. Leaves of trees and shrubs rank top of their preferred food, followed by herbs and grasses. Non-plant material consumed include spider webs, termite mounds and even cremated human remains. They forage on agricultural crops and other human foods, and even accept handouts. Although they occasionally drink, langurs get most of their water from the moisture in their food.
Gray langurs exist in three types of groups:
- uni-male groups, comprising one adult male, several females and offspring;
- multi-male groups, comprising males and females of all ages;
- all male groups.
All-male groups tend to be the smallest of the groups and can consist of adults, sub-adults, and juveniles. There are some populations that have only multi-male groups as mixed sex groups while others have only uni-male groups as mixed sexed groups.
Some evidence suggests that multi-male groups are temporary and exist only in the transition period following a takeover during the mating season and soon split into uni-male and all-male groups.
Social hierarchies exist for all group types. In all-male groups, dominance is attained by displacing another member, chasing, fighting, copulatory success, and harassment. With sexually mature females, rank is based on physical condition and age. The youngest females rank highest and they drop in rank as they age. Aggressive and submissive interactions occur more often between high-ranking individuals in a group. Most changes in social rank in males are associated with emigration and immigration. An adult male may remain in a uni-male group for 45 months. The rate of male replacement can occur quickly or slowly depending on the group.
Females within a group are matrilineally related. Female memberships are also stable, but less so in larger groups. Relationships between the females tend to be friendly. They will eat, move and rest together and embrace, and greet each other. They will also groom amongst themselves with grooming directed both up and down the dominance hierarchy. However higher-ranking females give out and receive grooming more than lower ranking females. In addition, females groom males more than the other way around. Males and females in a group tend to be calm and cooperative. Relationships between males can range from peaceful and cooperative to agonistic. While females remain in their natal groups, males will leave when they reach adulthood. Relationships between groups tend to be agonistic. High-ranking males from different groups will display, vocalize, and fight among themselves.
Reproduction and parenting
In uni-male groups, the resident male is usually the sole breeder of the females and sires all the young. In multi-male groups, the highest ranking male fathers most of the offspring followed by the next ranking males and even outside males will father young.
Higher ranking females are more reproductively successful than lower ranking ones. They will mate both polygynously and polygamously.
Female grey langurs show no external sign that they are in a reproductive state. However, males seem to be able to deduce the reproduction state of female though some unknown means. Females will solicit copulation by shuddering the head, lowering the tail, and presenting the anogenital region. Solicitations are not always successful in achieving a copulation. When langurs mate, they are sometimes harassed by other group members. Females have even been recorded mounting other females.
The gestation period of grey langur lasts around 200 days, at least at Jodhpur, India. In some areas, reproduction is year-around. It appears that year-round reproduction occurs in populations that capitalize on human made foods. Other population have seasonal reproduction.
Infanticide is common among gray langurs. Most infanticidal langurs are males that have recently immigrated to a group and driven out the prior male. These males only kill infants that are not their own. Infanticide is more commonly reported in uni-male groups, possibly because situations where one male breeds drive the evolution of this trait. In multi-male groups, the costs for infanticidal males are likely to be high as other resident males might defend the victim, and the benefits may be low due to the lower parental probability in multi-male groups. Nevertheless, infanticide does occur in these groups, and is suggested to be a male reproductive strategy intended to shorten the female’s interbirth interval and sire her next offspring.
Females usually give birth to a single infant, although twins do occur. Most births occur during the night. Infants are born with thin dark brown or black hair and pale skin. Infants spend their first week clinging to their mothers’ chest and suckling, or sleeping. They do not move much in terms of locomotion for the first two week of their life. As they approach their sixth week of life, infants vocalize more.
They use squeaks and shrieks to communicate stress. In the following months, the infants are capable of quadrupedal locomotion and can walk, run and jump by the second and third months. Alloparenting occurs among langurs, starting when the infants reach two years of age. The infant will be transferred among the group females. However if the mother dies, the infant usually follows. Langurs are weaned by 13 months.
- lough calls or whoops made only by adult male during displays;
- harsh barks made by adult and subadult males when surprised by a predator;
- cough barks made by adult and subadult during group movements;
- grunt barks made mostly by adult males during group movements and agonistic interactions;
- rumble screams made in agonistic interactions;
- pant barks made in conjunction with loud calls during inter-group interactions;
- grunts made in many different situations, usually in agonistic ones;
- honks made by adult males during inter-group interactions;
- rumbles made during approaches, embraces, and mounts;
- hiccups made by most members of a group when another group is sighted.
Status and conservation
While many populations of gray langurs are stable, in some areas they are declining, and both the black-footed gray langur and Kashmir gray langur are considered threatened. The latter is the rarest species of gray langur with less than 250 mature individuals remaining.
In India, langurs number at around 300,000. India has laws prohibiting the capturing or killing of langurs. Enforcement of these laws have proven to be difficult and it seems most people don’t know they are protected. The natural habitat of gray langurs is threatened by encroachment and plantation and slash-and-burn agriculture. Other threats include open cast mining, fire damage, grazing, ground litter removal, and non-timber forest products including wood for fuel, fodder, fruits, gums, seeds, and medicinal plants.
Langurs can be found near roads and can become victims of automobile accidents. This happens even in protected areas with deaths by automobile collisions making nearly a quarter of mortality in Kumbhalgarh Wildlife Sanctuary in Rajasthan, India. Langurs are considered sacred in the Hindu religion and are sometimes kept for religious purposes by Hindu priests and for training for roadside performance. However there are some groups of different religions that will hunt langurs for medical purposes and parts of gray langurs are sometimes kept as amulets and seen as having positive effects for the bearer.
Because they are considered sacred and also due to their less aggressive behavior compared to other primates, langurs are generally not considered pests in many parts of India. Nevertheless, attitudes have somewhat changed partly due to secularization. Langurs will raid crops and steal food from houses and this causes people to persecute them. People will feed them in temples, but treat the ones they find at home as a nuisance. Langur stealing and biting people to get food in urban areas may also contribute to more persecutions.
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