Western lowland gorillas feed on grasses, herbs and sedges that thrive in forest clearings and gaps in the canopy, and so are often found in areas of secondary forest. Social organisation takes the form of single-male harems, with female transfer and male emigration at maturity.
At Mbeli Bai in the Nouabale-Ndoki National Park in northern Congo, group size varies from two to sixteen, with an average group size of 9.4 individuals. Females often transfer to another group before breeding, usually when they become adolescent at around eight years old, and sometimes transfer several times during their life. Females do not usually form bonds with other females, but bond instead with their own offspring and the group silverback, so that the silverback is the cohesive influence that holds the group together. When a silverback dies, groups typically disintegrate and females immigrate into new groups.