Females, male competition and gray langur troop structure

During the course of an ongoing investigation of the effects of mother-infant separation on development in gray langur monkeys (Presbytis entellus), a series of 4 mothers of approximately 6-month-old infants were removed from their social groups and placed in a captive all-male group for 2-week periods. The male group contained 3 sexually mature animals and 1 juvenile and was within the range of variation observed in the wild. One of the introduced females came into estrus while with the male group. Agonistic behavior among the males increased during her introduction, but was resolved through dominance. There was no fighting and little threat. Agonistic behavior did not increase during the introductions of the other 3 females. These results are discussed and it is proposed that dominance can allow the survival of multi-male troops among gray langurs where (1) low population densities allow the formation of hierarchies, and (2) existing hierarchies are not disrupted by the simultaneous presence of several estrous females. It is predicted that these conditions will best be met where troop sizes are moderate and mating is not sharply seasonal.