Cyclic proceptivity in a captive female orang-utan (Pongo Pygmaeus Abelii)

An adult male-female pair of orang-utans was observed for a 3-month period, commencing with the introduction of the animals to each other. After approximately 2 weeks, the female began to show proceptive behaviors towards the male. Two other proceptive periods were observed, occuring from 26 to 30 days apart, and lasting for 4-6 days. These female-initiated periods of sexual activity began with increased locomotor activity, solitary play, proximity to the male, following the male, and social grooming. The peak periods of proceptive behaviour included hand-genital contact, mouth-genital contact, rolling the male onto his back, both dorso-ventral and ventro-ventral mounting, and pelvic thrusting. Although hormonal levels could not be assessed in this study, it is believed that these peaks coincided with ovulation. In previous reports, the presence of proceptive behaviors was perhaps over-shadowed by highly aggressive sexual behavior on the part of male orang-utans. The visibility of proceptivity in this study is attributed to the large cage which allowed the female to escape the male's advances, enabled distance between the animals when they preferred it, and continuous exposure of the orangs to each other. This female orang-utan behavior was compared to the female sexual behaviours of the other great ape species - the chimpanzee and the gorilla.