Activity Patterns

Hanuman langurs are diurnal, sleeping in the trees and spending much of their day on the ground. They are generally active during the cooler parts of the day, in the morning and late afternoon, and rest during the middle of the day. This activity pattern is particularly distinct during the dry season, when it is hotter. During the active periods of the day the infants and juveniles play while the adults feed and look for food. Estrus females are active during the morning and afternoon periods of activity (Jay, 1965). In mountainous regions hanuman langurs migrate to lower elevations during the cold part of the year.

During the monsoon, from April to June, food resources are at their peak and hanuman langurs increase their activity. Mating season follows the monsoon because the females are physically healthy enough to ovulate regularly (Koenig, 1997). Also, mothers begin weaning their infants during the monsoon, because more digestable foods are present. Therefore, the reduction in lactation and the higher nutrition value enable females increase their health prior to the mating season.

Grooming and Resting

During the middle period of each day hanuman langurs rest and groom each other. This behavior is very important for establishing bonds within a social group. The adult males and females groom each other, with strongest grooming relationships existing between the dominant male and the adult females. The level of grooming interaction among adult hanuman langurs increases with rank of the adult. Strong grooming relationships exist between adult females and infants and juveniles, but males do not have grooming relationships with the young. The diagram on the right illustrates the social dynamics of grooming interactions. Females hanuman langurs participate in cooperative parenting behaviors (allomothering) by allowing one another to groom their young.

Grooming Interactions (Diagram Courtesy of Phillus Jay)

Fights Between Males

Males trying to take over a group of females will fight the resident male. These fights are vicious, and often result in the injury of one or both males. Older males often have scars from previous injuries. Fights between males for dominance over one-male groups are the most violent because only the winner will monopolize a group of females.

Infanticide

When a male becomes the dominant male in a one-male group he will kill the infants that are not weaned. This also occurs in multi-male groups when the dominant male/s are replaced. New males in a multi-male group will also kill infants, but the male/s who are the likely father/s will defend the infants if they are present.. It has been noted that the new male will mate with the females shortly after takeover (Sugiyama, 1965; Mohnot, 1971; Vogel and Loch, 1984). The most accepted explanation for infanticide, the selection hypothesis, proposes that infanticide has evolved because of competition for reproductive access to female langurs. The hypothesis explains that males kill the infants in order to make lactating females ovulate, and to reduce the reproductive success of the resident male (Hrdy, 1974). Infanticide also occurs when all-male groups come into contact with a group with females. The males will try to kill infants of all ages in order to weaken the dominant male of the group (Newton, 186).

Photo courtesy of Jim Steinhart

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