Updated
Gorillas mate year-round, without a fixed breeding season. A female is fertile for only one to three days in a cycle of about a month, and she usually initiates mating by approaching a male, often the dominant silverback, with glances, body postures or gestures. Mating is brief and frequently happens in the open. In mountain gorilla groups with more than one silverback, subordinate males also father some infants. After a pregnancy of about eight and a half months, a single infant is born, which nurses for three to four years. Here is how gorilla reproduction works.
Who mates with whom
In a group with one silverback, he fathers almost all infants. Mountain gorillas, however, often live in multi-male groups, and genetic studies in the Virungas have shown that subordinate silverbacks father a meaningful share of offspring, which may encourage them to stay and help defend the group. Females choose too: they transfer between groups, typically as young adults, and may leave a male who fails to protect them. Same-sex sexual behaviour has also been recorded between females in the Virunga gorillas. See our guide to what makes a silverback.
Maturity and the breeding cycle
Females reach sexual maturity at around eight years and usually give birth for the first time at about ten. Males mature at a similar age but rarely breed until they become silverbacks at about 12–15 years and win access to females. Because each infant nurses for years, and a female does not usually conceive again until weaning is near, births are typically about four years apart. A female may raise only four to six surviving offspring in her life, which is why gorilla populations recover so slowly.
Pregnancy, birth and nursing
Pregnancy lasts about 255 days, roughly eight and a half months, and is hard to spot until late. Births usually happen in the nest. The newborn weighs around 2 kg and clings to its mother’s chest, nursing frequently; from a few months old it rides on her back and starts to taste plants, but milk remains important until weaning at three to four years. See our guide to baby gorilla development.
Threats to reproduction
When a new male takes over a group, he may kill unweaned infants, which brings their mothers back into breeding condition sooner; this infanticide is a leading natural cause of infant death. Disease, snares and the death of a group’s protector also reduce breeding success. Ranger protection and veterinary care have helped mountain gorillas grow to just over 1,000. See our guide to threats to gorillas in the wild.
On a trek
Mating is occasionally seen during the hour with a family, usually briefly. Stay quiet and keep your distance, as at any other time. You are more likely to see infants of different ages, a good sign that the group is healthy. See our guide to gorilla family life. The permit costs US$800, or US$600 in April, May and November.
Frequently asked questions
No. They mate and give birth year-round.
Mostly, but in multi-male mountain gorilla groups subordinate males also father infants.
About every four years.
Females give birth first at about ten; males usually breed once they are silverbacks.
