There is no special breeding season and gorillas may mate at any time of the year. It is not always the lead male in a group who mates with the females in his group; sometimes a wandering male who has joined a group for a while mates with a female in it. He may take a female with him when he leaves, to form a new group.
A female is ready to breed when she is 6 - 7 years old and she usually has a baby about every four years. Infant mortality is quite high and about 40 - 50 per cent of the young die in infancy. Therefore, a female probably produces a baby more frequently than once every four years.
Gestation (the time between conception and birth) is 251 - 295 days, a little shorter than in the human. The baby gorilla weighs about 1.98kg, just about half the normal weight of a human baby at birth. However, the baby gorilla develops twice as fast, crawling in 9 weeks and walking upright for a few steps at 35 - 40 weeks. Most babies are weaned after 8 months but some continue to suckle for up to 20 months. Gorilla parents protect their offspring at all times, so the young apes are able to spend their 'childhood' eating, sleeping and playing.
A youngster stays with its mother for about three years. Females stay in the group but males wander off to live a mainly solitary life, becoming sexually mature at 8 - 9 years, but they do not reach full size until they are 12 - 14 years old.Read More: Gorillas and Humans