Social interactions of orphans observed in a free-ranging troop of Japanese monkeys.

During 4 years of observations of a troop of free-ranging Japanese monkeys, more than 40 'orphans', young monkeys who lost their mothers, were found. Most infants who lost their mothers before the weaning period could not survive, while young animals over 1 year old could survive their mothers' deaths. Adult males of the troop and immature close relatives were observed to become the caretaker of these orphans. With a few exceptions, adult females were indifferent to orphans. Grooming behavior, rank, solitariness of males, and maternal behavior of females are compared between orphans and non-orphans.