Mountain gorillas are polygynous; the dominant male in each group has exclusive access to all the females in the group.
Mating System: polygynous
Reproductive rates are slow and a female may leave only 2 to 6 offspring over a 40 year life-span. Males that have a harems of 3 to 4 females increase their reproductive output by fathering 10 to 20 offspring over 50 years. These animals don't mature sexually until well into their teens.
Mating behavior is initiated by the female, with a series of slow and hesitant approaches to the male. A female is receptive only during estrus, and she will cease to ovulate for several years after giving birth. The length of the estrous cycle of a female mountain gorilla is 28 days, and there is no visible external menstrual flow.
A single, dependent young is born after a eight and a half month gestation period. Weaning often doesn't occur until three years of age, and juveniles may remain with mothers for years after that. Females are sexually mature by 10 years of age, but males are unlikely to start breeding before 15 years. Reproductive output for females is about one surviving offspring every 8 years (survival implying reaching breeding age).
Breeding interval: The interval between reproductive events depends upon infant survival. Females are capable of producing an infant every 4 to 5 years.
Breeding season: These animals breed throughout the year.
Average number of offspring: 1.
Average gestation period: 8.5 months.
Range weaning age: 36 to 48 months.
Average age at sexual or reproductive maturity (female): 10 years.
Average age at sexual or reproductive maturity (male): 15 years.
Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); fertilization ; viviparous
Females provide most of the parental care in this species. Females nurse and carry their young for about 4 years. They also play with the young, teach them, and groom them.
The role of males in parental care is less direct, although no less important. Males protect the females and the young within their social group from potentially infanticidal rival males who may take control of the group.
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Male, Female); pre-weaning/fledging (Provisioning: Female, Protecting: Male, Female); pre-independence (Protecting: Male, Female); extended period of juvenile learning