How Gorillas Mate – The largest living ape today is the gorilla, which inhabits the lush forests of Central and Eastern Africa. These mostly herbivorous giants share about 98% of their DNA with humans, making them one of our closest living relatives. There are two main species of gorilla: the Eastern gorilla and the Western gorilla. Each species is divided into two subspecies: the mountain gorilla and the eastern lowland gorilla for the Eastern gorilla, and the Cross River gorilla and the western lowland gorilla for the Western gorilla.

Gorilla Groups and Family Hierarchy

A typical gorilla group consists of various family members, including infants, juveniles, adult males and females, and a dominant male who leads and guides the group on activities and movement. Gorilla groups usually contain around 30 individuals and are known for their peaceful nature, with few internal conflicts. Interactions between different gorilla groups are rare, although they have been noted among the western lowland subspecies. This rarity explains why you can’t encounter all the gorillas in one park during gorilla trekking; you can visit one gorilla family at a time. Lone males or other groups may occasionally challenge the group, resulting in violent confrontations. The silverback, with the help of other mature male gorillas, can defend his family in such cases.

Breeding in Gorillas

In gorilla groups, the dominant male, known as the silverback, breeds with all the females. Mating occurs year-round and is usually initiated by the females, regardless of whether they are in estrus. Both western and eastern gorillas are known to mate while facing the same side, though instances of face-to-face mating have been observed, particularly among mountain gorillas.

Sexual Maturity and Reproduction in Gorillas

The reproductive habits of gorillas are influenced by various factors, so understanding their reproductive cycle is key. Female gorillas reach sexual maturity between the ages of 10 and 12, although their ovulation cycle begins earlier, around age 6. However, they remain infertile until they reach full maturity at age 10. Many females leave their father’s group to avoid inbreeding, while those who stay attempt to avoid mating with their father, often choosing less dominant males instead.

In contrast, males leave the group upon reaching maturity, either becoming loners or joining bachelor groups. Later, they may steal females from other groups to form their own family units. Despite the strong bonds the dominant silverback forms with the females in his group, as he ages and his reproductive capacity declines, the females often leave to join other groups. Some may remain loyal to the silverback, but will ultimately join other groups after his death. Females may change groups multiple times to protect their offspring, especially if a new dominant silverback takes over.

How Gorillas Mate

Gorillas mate throughout the year, with the dominant silverback mating with all the females while they are ovulating. Mating is usually initiated by the sexually active female, though the silverback may also initiate by approaching the female, touching her, or making displays with sounds. If the female does not respond positively, the silverback may react aggressively, charging or slapping the female to force acceptance.

Mating typically occurs on the ground, with the female (usually smaller than the dominant silverback) kneeling while the male copulates on top. However, some gorilla subspecies, such as mountain gorillas and lowland gorillas, have been observed mating face-to-face, a behavior once thought to be unique to humans and bonobos.

Signs a Female Gorilla is Ready to Mate

Unlike chimpanzees, female gorillas don’t show physical changes when they’re ready to mate. Instead, a female gorilla signals her readiness by gently approaching the male, pressing her lips together, and making prolonged eye contact with him. If the male does not respond to her advances, she may slap the ground and move towards him to attract his attention. Sometimes, if the dominant male is unresponsive or preoccupied, the female may mate with less dominant males in the group.

A study conducted in 1982 revealed that due to aggression from the silverback towards a particular female, she was compelled to initiate mating even when not in estrus.

Do Gorillas Only Mate for Reproduction?

In general, gorillas do not mate for leisure or competition. However, females often mate to gain favor with the dominant silverback and prevent him from mating with other females in the group. Expectant females have been known to mate with the silverback to prevent him from impregnating other females ready to mate. Silverbacks typically prefer mating with experienced adult females, which can lead to competition among the female gorillas. In the western gorilla species, silverbacks may mate with females regardless of their ovulation status, though most females will only mate when they are sexually ready.

Reproduction and Parenthood

When mating is successful and a female gorilla conceives, she undergoes an 8.5-month gestation period and gives birth about every four years. During pregnancy, the female’s breast size increases slightly and she develops a subtle tummy bump. Birth typically occurs in the morning, often preceded by the female’s restlessness, stretching, and loss of appetite.

Throughout her lifetime, a female gorilla may give birth to six to eight babies, but only a few are likely to survive to maturity, as the female provides all of the care. The silverback male plays a crucial role in ensuring the babies are accepted within the group and are not bullied by other members. For the first five months, the mother stays close to the silverback for protection.

Breastfeeding and Weaning Among Gorillas

For the first four months of their lives, infant gorillas are carried by their mothers, who nurse them directly every three hours. By the fifth month, infants start gaining confidence and ride on their mothers’ backs, sometimes lying on the ground nearby. By the time they reach one year old, baby gorillas have enough confidence to venture up to five meters away from their mothers for brief periods. By the age of two, they can spend more time away from their mothers but will still return to them. Weaning typically occurs when the baby gorilla is around 2.5 years old. However, they may continue to nurse until about four years of age. Once they stop nursing, they start making their own nests and become more independent, while their mother resumes ovulation.

Infant Gorilla Mortality

Despite being considered endangered, gorillas face high infant mortality rates, with nearly half not reaching adulthood.

• Group Leadership Changes: When a new silverback takes over a group, he often kills nursing infants to create opportunities for successful mating with the females.

• Trauma: Trauma accounts for approximately 56% of infant mortality in gorillas.

• Respiratory Infections: Nearly 15% of infant deaths are due to respiratory infections.

• Illnesses: Various illnesses, such as hepatic capillariasis, gastrointestinal parasitism, and lymphoid disease, contribute to infant mortality, particularly among mountain gorillas.