There are huge differences in appearance between male and female gorillas, with males weighing twice as much. Adult males also have several secondary sexual charactistics: a prominent sagittal crest (to which their powerful jaw muscles are attached), large canines, a wide, smooth, hairless chest and white fur covering their back and the top of their thighs (giving them the name ‘silverbacks’).
 
Gorillas are the largest primates. They move about mainly on the ground and sleep in nests that they building from leaves in just a few minutes and use for a single night. Groups contain a dominant male, several adult females and their young of varying ages. Each animal has a precise hierarchical status within the group.
 
On attaining sexual majority at the age of about 6 or 7 years, females leave their birth group to join another group or found a new family with a solitary male. They may change group several times in their life.
 
Adolescent males or ‘blackbacks’ also leave their birth group to live alone or to join, temporarily, other males before they are able to attract their first female and head their own group. A silverback reaches full sexual maturity at about the age of 18 years.
 
Despite their impressive physique, gorillas are timid and reserved by nature. When disturbed or threatened, males try to intimidate the intruder by shouting and hitting their chest with their fists.
 
All sub-species of gorilla are endangered through the destruction of their habitat, being hunted for their meat or for the illegal trade in their young, by armed conflicts despoiling their territories and by living too close to humans, who sometimes pass on diseases.