Most mammals copulate around the period of ovulation when there is a high probability of conception.
In bonobos, females show perineal swelling for about 14 days in a menstrual cycle of 35 days. Most of copulation occur druing this estrous period. However, in some circumstances, females show continuous perineal swelling throughout the menstrual cycle and copulate with males.
When they have a baby, great apes other than bonobos do not show cyclic estrus unti the baby is weaned at the age of 3 to 4 years. However female bonobos show cyclic estrus even during this period though they don't conceive until the baby is weaned.
Thus the female bonobos seem to use copulation for some social purposes other than reproduction.
A female sometimes grasps the testicles of her mate in a climax of copulation.
Bonobos have a great variety of sexual behaviors other than copualtion. Those behaviors seem to have social roles to reduce tension, to greet, and to build or maintain familiar relations. Genito-genital rubbing、Rump-rump contact、Sexual behaviors of immature animals
