Reproductive habits of chimpanzees
Sexuality in the members of the genus Pan is very different from that of other animals. They practice sex not only to reproduce but also with some social purposes.
However, the sex habits are different between both species. Bonobos stand out in this area because they use copulation to resolve conflicts, to greet each other, as a form of reconciliation after a physical struggle, as a resource to calm the offspring and as a currency for food. In short, sexual relations are part of their daily activities, performed not only when they are in heat.
Sexual relationships are not exclusive when they are in heat; they also use them for social purposes.
Regarding their sexual practices, the intercourse is face to face, something that was believed to be unique in wild animals, but later it was found that gorillas do the same. Besides copulating in different positions, they can do it with members of the same gender, with younger or older individuals and even with offspring and other relatives. However, encounters of mothers with their children even if they are adults are extremely rare, and they often avoid them.
There is more information about the reproduction of common chimpanzees since this species has been more researched. Their sexual relations are not for the exclusive purpose of producing offspring, they also have several social functions, but their practice may not be as diverse as those of the bonobo, and females do not reproduce frequently.
Both the common chimpanzee and the bonobo mate with many individuals throughout their lives. During one mating season one or two males can breed with two or more partners almost exclusively, but occasionally a male prevents others from mating with a specific female. This exclusivity only happens among common chimpanzees, because only the highest-ranking male can mate with a particular female.
Both species reach sexual maturity between 10 and 13 years of age. Females become sexually attractive around 10 or 11 years old and have their first offspring some time later. Approximately, they give birth to a single infant once every five years, even the bonobos. Common chimpanzees have a 36-day estrous cycle.
Courting and mating
When a female is in heat, the anogenital region swells and acquires a pink hue, which indicates males that she is available to mate. It is during this period that most of the mating with mature males occur. Bonobos remain “swollen” for about 10-20 days, and common chimpanzees, an average of 6.5 days. Typically, females experience a sterile stage, and after that, they can get pregnant.
Once the males know that a female is in heat, they focus on attracting her by showing their genitals. She can accept or reject the invitation to copulate; If the answer is affirmative, she approaches the male and mate. As several males court them and mate more than once during the heat, it is hard to know who the father of their offspring is.
Care of the offspring
The gestation period lasts about eight months. The offspring is born at any time of the year. Bonobo females usually show signs of being in heat a year later but are unlikely to be fertile. In any case, the chimpanzee mothers take care of their infants, and when the latter still cannot do it by themselves, they transport the little ones on their back or in the lower part of their body.
The offspring are entirely dependent on their mother, and are extremely vulnerable to predators and even to other male chimpanzees, as some tend to kill them to eliminate the offspring of their rivals. Between four and six years of age, mothers wean the young and their youth stage begins, characterized by the interaction with more members of the community. Between seven and ten years of age (up to 12 years in the case of males), they are considered adolescents and become adults when they reach sexual maturity.
Christophe Boesch. The Real Chimpanzee: Sex Strategies in the Forest. Cambridge University Press, 2009.
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