Orangutans

Abstract

Orangutans have a number of unusual features that contribute to their highly diverse sexual behavior. Like humans, they do not have an estrous, or sexual, swelling, and males probably cannot tell when a female is ovulating. They have the longest interbirth interval of any mammal, leading to intense male–male competition over mates. Males can occupy two sexually mature morphological forms: flanged and unflanged. Both flanged and unflanged males may force females to copulate, leading to one of the highest rates of forced copulation in animals. Female choice is evidenced by females actively seeking flanged males when they are ovulating and through their higher likelihood of mating with nonpreferred males when they are not ovulating, possibly serving as a paternity confusion strategy. Orangutans show a range of other sexual behaviors, such as oral sex, by both males and females, very long copulatory periods, face‐to‐face copulation, and some same‐sex sexual interactions.