Anup Shah / Western lowland gorilla (Gorilla gorilla gorilla) sub-adult female 'Mosoko' aged 8 years crossing a river, Bai Hokou, Dzanga Sangha Special Dense Forest Reserve, Central African Republic

Andy Rouse / Mountain gorilla (Gorilla beringei) silverback in Susa group, Parc National des Volcans, Rwanda

Andy Rouse / Mountain gorilla (Gorilla beringei beringei) silverback male portrait, Volcanoes NP, Virunga Mountains, Rwanda

John Sparks / David Attenborough with mountain gorillas, on location during filming for BBC 'Life on Earth' series in Rwanda 1978

Gerry Ellis / Western Lowland Gorilla (Gorilla gorilla gorilla) silverback, Limbe Wildlife Centre, Cameroon

Mary McDonald / Adult Mountain gorilla (Gorilla beringei beringei) holding baby, Hirwa group, Volcanoes National Park, Rwanda

Eric Baccega / Mountain gorilla (Gorilla beringei) juvenile aged 2 years, hanging from branch, member of the Nyakagezi group, Mgahinga National Park, Uganda. January.

Pedro Narra / Mountain Gorilla (Goriila beringei) resting, Volcanoes National Park, Virunga Mountains, Rwanda.

Christophe Courteau / Mountain gorilla (Gorilla beringei beringei), silverback and juvenile son. Volcanoes National Park. Rwanda.

Christophe Courteau / Mountain gorilla (Gorilla beringei beringei), dominant silverback in forest clearing. Volcanoes National Park, Rwanda.

Christophe Courteau / Mountain gorilla (Gorilla beringei beringei) blackback, juvenile male demonstrating power. Volcanoes National Park, Rwanda.

Christophe Courteau / Mountain gorilla (Gorilla beringei beringei) blackback, juvenile male demonstrating power. Volcanoes National Park, Rwanda.