Bernard Castelein / Hoolock Gibbon (Hylobates hoolock) male hanging from a branch. Assam, India, February.

Anup Shah / Siamang gibbon male calling, pouch inflated

Anup Shah / Grey gibbon portrait

Rod Williams / Young male Black Concolor gibbon portrait {Hylobates concolor} occurs Vietnam, N Laos, Isle of Hainan

Rod Williams / Face portrait of female Black gibbon, occurs SE Asia

Robin Chittenden / Siamang Gibbon (Symphalangus syndactylus) Thrigby Hall zoo, Norfolk, England, UK, November.

Bernard Castelein / Malayan Giant Squirrel (Ratufa bicolor) climbing tree, Gibbon Wildlife Sanctuary, Assam, India

Matthew Maran / Black gibbon {Hylobates concolor} captive female, Endangered Primate Rescue Center, Cuc Phuong National Park, Vietnam

Matthew Maran / Black gibbon {Hylobates concolor} captive female, Endangered Primate Rescue Center, Cuc Phuong National Park, Vietnam

Matthew Maran / Black gibbon {Hylobates concolor} captive female, Endangered Primate Rescue Center, Cuc Phuong National Park, Vietnam

Anup Shah / Siamang gibbon male displaying

Anup Shah / Grey gibbon