Social and Reproductive Behavior of Wild Adolescent Female Orangutans

Abstract

At Tanjung Puting, adolescent female orangutans were the most social of all age/sex classes and should not be described as solitary or even semi-solitary. Non-exclusive groupings involving adolescent females and subadult males were the associations most commonly seen at Tanjung Puting. Adolescent female interactions with adult males were almost totally restricted to consortships which the female initiated, maintained, and terminated. Adolescent female interactions with adult females were largely absent due to adult female agonism. This agonism probably relates to child-care constraints and food competition experienced by the adult female. Adolescent female interactions with subadult males involved long term associations in which no copulations took place and short term (<1 day) association in which “resisted mating” occurred. Overall, heterosexual associations were social. Adolescent females did not consort with subadult males. Adolescent female interactions with their own age/sex class were invariably social, and adolescent females always traveled together following encounters. Adolescent females were the only age/sex class observed to carry out interunit grooming. First parturition for wild orangutan females is estimated at approximately 14 or 15 years of age. Adolescent females experience a period of sterility which may exceed one year prior to first parturition. Adolescent females copulate at higher rates than do adult females. Adolescent females were the only age/sex class at Tanjung Puting to display high levels of proceptive behavior. This proceptive behavior, while not always successful, appeared crucial to inducing consorts to copulate. Adolescent females preferred adult males as sexual partners, but themselves were not preferred by adult males. A large amount of learning appears to take place during the orangutan’s adolescence as a result of increased sociality. Due to their small size, rapid travel and long day ranges, sociality probably is not as costly for adolescent female orangutans as it is for adults. Adolescent females probably benefit from associating with other orangutan units because, based on the age/sex class they are associating with, grouping provides: a) a potential context in which to learn adaptive solutions to social and/or environmental problems, b) increased foraging efficiency, c) protection from predators and/or “enemies,” and d) a potential context in which dominance and affiliative relations between individuals can be developed.