Introduction To Chimpanzee Mating

The reproduction of chimpanzees is very complicated due to the many misconceptions that came up early into the study of their mating system. Males and females are known to have more than one partner, making them polygynandrous (they have multiple partners). Sometimes, a male may control access to a certain female, barring her from any other male who may try to mate with her. He can do this in two ways, either by dominance or force, or by taking the female on a courtship away from the males and therefore securing her from the other males.

    It’s important to remember that the copulation may serve many social functions for chimpanzees. For example, chimpanzees mate more than necessary to guarantee pregnancy. Mating may also strengthens bonds between the two. It can also be a start to establishing and maintaining group unity.

    Females have a cycle which last about 1.5 months (36 days). During the cycle, her hormone levels change and they experience changes in the size, shape, and color of her genital skin. Estrogen will increase during the follicular phase of her cycle and the size of the swelling. When the skin is fully engorged, it is usually bright pink, and measure anywhere from 938-1400mL (cc). This is also when most of the copulations will happen.

    The swelling of the female’s anus controls the sexual behavior in the animals. Most copulations involving mature males and females (96.2%) seen at the Gombe Stream National Park in Tanzania was observed when the females were swollen to their maximum. The role of the swelling is there for many reasons. Firstly, it is a signal to the males that a female is ready for sexual activity. Females are solitary animals, which mean that they usually live alone, so it is necessary for them to communicate to the males that they are ready to mate. Also, the males are interested in the condition of the female’s genitals that they may encounter. Lastly, the swelling can also mean that the female will be able to take in more nutrients to be able sustain a potential baby.