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

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

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) silverback sitting on boundary wall between Volcanoes National Park and a Potato crop, looking into valley. Area to be restored to forest. Rwanda.

Christophe Courteau / Family of Mountain gorillas (Gorilla gorilla beringei) with a silverback, grooming and looking around, part of the HIrwa Gorilla Group, Volcanoes National Park, Rwanda.

Fiona Rogers / Mountain gorilla (Gorilla gorilla beringei) silverback male feet, member of 'Humba' group. Virunga National Park, Democratic Republic of Congo, March.

Andy Rouse / Mountain gorilla (Gorilla beringei) silverback yawning with mouth wide open. Rwanda.

Andy Rouse / Mountain gorilla (Gorilla beringei beringei) mother with young, and silverback in background. Virunga Mountains, Rwanda. Non-ex.

Jabruson Motion / Silverback Western gorilla (Gorilla gorilla) 'Makumba', leader of the 'Makumba' troop, breaking into a termite's nest in order to feed, Bai Hokou, Dzanga-Ndoki National Park, Central African Republic

Jabruson Motion / Silverback Western gorilla (Gorilla gorilla) 'Makumba', leader of the 'Makumba' troop, breaking into a termite's nest in order to feed, Bai Hokou, Dzanga-Ndoki National Park, Central African Republic