Western gorillas live in relatively small groups of only about six animals, lead by dominant males, or silverbacks - so-called because of the grey-white fur only found on the backs of older males. Although gorillas are large and extremely powerful, they are gentler than chimpanzees.
Gorilla groups tend to avoid one another although, on occasion, groups will meet amicably for a short time. Sometimes meetings are not peaceful, and a dominant silverback may respond to intruders by standing up, hooting and beating his chest with cupped hands, followed by a display of strength by breaking branches. This display may lead to an all-out attack.