Gorillas: Family groups
The big adult males are so huge, weighing up to 275 kilograms, that only the stoutest trees can support them. They climb rarely and do not have much reason to, for although the shape of their teeth and the nature of their digestive system suggest that they were once primarily fruit-eaters, like the Orang Utan, they now subsist very largely on vegetation that can be reached without climbing, such as nettles, bedstraw creeper and giant celery. Usually, they also sleep on the ground, making a bed among the flattened vegetation on which they have fed. They live in family groups of a dozen or so, each being led by a silver-backed patriarch, who has several adult females attached to him. They sit quietly grazing, ripping huge handfuls of stems from the ground with slow, irresistible sweeps of their immense hands, lolling among the dense nettles and celery, sometimes grooming one another. For the most part they sit in silence. Occasionally they exchange quiet grunts or gurgles and if an individual wanders away from the main group it makes a belching sound every now and then so that the rest know where it is. While the adults doze, the young play and wrestle and occasionally rear up on their hind legs to beat a quick tattoo on their chests, rehearsing the gesture the adults use in display. The silver-back leads and protects his group. If he is frightened or angered by intruders he may roar defiance and even charge. A blow of his fist can smash a man's bones. Pestered by a younger rival, who may be trying to lure away one of the females of his group, he will even fight although this is a rare event.