Development

A newborn gorilla weighs about 1.8 kg (4 lb), and spends its first few months of life in constant physical contact with its mother. They begin to walk around four or five months, and start to put plant parts in their mouths between four and six months. At eight months they regularly ingest solid food (Watts 1985). Weaning occurs around three years of age, although juveniles may remain with their mothers for years after that (Lindsley & Sorin 2001).

Young male and female gorillas are considered infants from birth until three years of age, juvenile between the ages of about three and six, and subadult from six to about eight years old. Blackbacks are sexually immature males from around eight years until they have developed the silver saddle and large canines of maturity (Groves & Meder 2001).

Reproduction

Females begin to ovulate at 7 or 8 years of age, and have their first infant between the ages of 10 and 12. Males, generally do not start breeding before the age of 15 (IGCP).

Mountain Gorillas have no mating season. Females usually initiate mating behavior. The length of their estrus cycle is about 28 days with 1-3 fertile days, and ovulation ceases for 3–5 years after reproducing. The length of gestation is eight and a half months. Females generally rear one infant every 6 to 8 years, and may leave only 2–6 offspring over a 40 year life span. Males that have a harems of 3–4 females increase their reproductive output by fathering 10-20 offspring over 50 years (Lindsley and Sorin 2001).

When the dominant silverback dies or is killed by disease, accident, or poachers, the family group may be severely disrupted ("Mountain Gorillas," 2003). Unless he leaves behind a male descendant capable of taking over his position, the group will either split up or be taken over in its entirety by an unrelated male. When a new silverback takes control of a family group, he may kill all of the infants of the dead silverback (Fossey 1984). This practice of infanticide is an effective reproductive strategy in that the newly acquired females are then able to conceive the new male's offspring. Infanticide has not been observed in stable groups.
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