Gray langurs, also known as Hanuman langurs, are members of the Semnopithecus genus, which contains seven species of Old World monkeys. Members of this genus can be found in a large range on the Indian subcontinent, preferring to reside in forested areas or semi-wooded areas at low or moderate elevations, although some species can be found as high as 13,000 feet above sea level. Until 2001, Semnopithecus entellus was the only species classified within this genus. When it was separated into seven species, some experts suggested that these species remain monotypic, while others suggested that the genus should only hold two species with many subspecies.
Gray langur species reach an average body length between twenty and thirty one inches, with a tail length between twenty-seven and forty inches a weight of twenty-four to forty pounds, depending upon the sex. It has been found that species in northern areas of this genus’ range are larger than those in the south. Most of the species within this genus are gray, but some can be yellowish in color, while all have black ears and faces. Species differ in color slightly and some have crest markings while others do not.
Gray langurs are active during the daytime hours, resting in trees and manmade structures during the night. These species can reside in a number of different groups, including groups with one male and several females, groups with many males and females, and groups with only males. Groups containing only males are typically the smallest and it is thought that multiple male groups only occur after one group has dominated another. Groups are known to be violent when encountering each other.
All groups contain a social hierarchy, although these hierarchies differ between types. In all male groups, dominance is gained by breeding the most and by aggression, while in groups with large amounts of females, the youngest breeding female is most often dominant. Within these female groups, most females are social with one another and many will form close relationships. Grooming and other social activities are often seen, although dominant females take part in grooming more often than other females.
In one male groups, there is no competition between males, so the dominant male will mate with all breeding females. In groups with multiple males, the dominant male will breed with the most females, but these are often higher-ranking females, leaving lower ranking males to fight for breeding rights over lower ranking females. Although females do not show that they are physically ready to breed, they will show males that they want to mate by sticking their lower regions into the air.
The breeding season of every species of gray langur is not known, but it is known to breed throughout the year in some areas. Females give birth two one or two young, typically at night, which are brown with brown or black fur. Young will attach themselves to their mother’s chest and stomach for the first week of life and will be weaned at thirteen months of age. Males will leave their birth groups once they are weaned. Infanticide is known to occur, typically caused by new males that have just taken over a group.
Gray langurs are herbivores, consuming a variety of food types including leaf buds, fruits, pines and cones from coniferous trees, lichens, roots, bamboo, and mosses, among other plant materials. They will also consume human foods, spider webs, and insect larvae. These species can make a wide range of vocalizations including whoops emitted by males, grunts, honks, and loud barks when threatened by predators, which include leopards, tigers, and wolves.
The population numbers of gray langur species vary, with the black-footed gray langur and Kashmir gray langur holding the lowest population numbers. Threats to gray langur species include illegal hunting and human encroachment. Langurs are thought to be a pest in some areas, but because they are not as aggressive as other primates are, they have a good reputation in most areas.
Image Caption: Alpha male Grey Langur at Mudumalai National Park. Credit: Marcus334/Wikipedia (CC BY-SA 3.0)