Female gorillas reach sexual maturity at 8 years. Before they become sexually active, they will normally leave their original troop and thus avoid inbreeding; inbred offspring can have crossed eyes and webbing between the fingers.
Gorilla ladies are fertile for 1–3 days a month and often initiate contact; they can choose among all adult gentlemen in the group. Gorilla sex is rare and short, sometimes less than a minute. George Schaller described it like this:
The female rises and stands by the rump of the male. He glances up and they stare at one another. The process of pulling her into a sitting position is repeated. At about seventy-five thrusts he begins his copulatory sound. His eyes are closed, and the thrusts rock her back and forth, a motion added by his hands on her hips and the swaying of her body. His lips are pursed and hers are slightly parted. At about one hundred and twenty thrusts the male suddenly opens his mouth with a loud sighing ‘ahh’, the female opens her mouth at the same time. He relaxes, she rises and leaves.
Pregnancy takes 8.5 months and there are typically 3–4 years between births. A mother may successfully raise 4–6 children during her lifetime of 30-40 years. Infant mortality is high—about 30% kids die of various natural causes before the age of 6; experienced mothers tend to be more successful. Unexpectedly, habituated troops have higher growth rates than unhabituated troops for reasons that are unknown; medical supervision may be a factor.
At birth, baby gorillas weigh 1.5–2kg (3.3–4.4lb). Newborns are 100% dependent on their mothers and remain so for 5 months. They then ride on their mothers’ backs for 4 months before becoming independent at around one year. However, they stay with their mothers until they are about 3 by which point they are fully weaned.
Eduard Reichenow, a German ornithologist, recorded capturing a few days old gorilla:
The whole body was sparsely covered with hair so that it almost appeared naked; only on the crown of the head there arose a straight tuft of long brown hairs. This manner of hair growth gave the little ape a particular human appearance. When one saw the little being, which flourished beautifully at the breast of a Negro nurse, in its helplessness, one had to become convinced that the gorilla nursling needs the greatest care and attention on the part of its mother.
Mothers are highly protective of their young; many have died trying to protect their offspring against poachers. Children learn so much from their mother and other troop members that it is very difficult to re-introduce young rescued gorillas into the wild.
This was an adapted excerpt from the award-winning Gorilla Highlands Interactive eBook.