Heather Angel / Northern white cheeked gibbon (Nomascus leucogenys) female standing in tree with baby aged two weeks. Parents captive bred and released. Wild Elephant Valley / Xishuangbanna, Yunnan Province, China, 2...

Magnus Lundgren / Wild Wonders of China / Central Yunnan black crested gibbon (Nomascus concolor jingdongensis), mother and baby hanging in canopy. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Rod Williams / Young male Northern White-cheeked Crested Gibbon (Nomascus leucogenys) Northern Vietnam. Critically Endangered, Captive

Shibai Xiao / Hainan black-crested gibbon (Nomascus hainanus) young male in tree, Bawangling National Nature Reserve, Hainan Island, China.

Heather Angel / Chinese white cheeked gibbon (Nomascus leucogenys) female hanging, carrying baby aged two weeks. Parents released into wild from captive breeding programme. Wild Elephant Valley / Xishuangbanna, Yunna...

Heather Angel / Chinese white cheeked gibbon (Nomascus leucogenys) female walking whilst carrying baby aged two weeks, holding on to vines for support. Parents released into wild from captive breeding programme. Wild...

Heather Angel / Northern white cheeked gibbon (Nomascus leucogenys) female hanging from tree with baby aged two weeks. Wild Elephant Valley / Xishuangbanna, Yunnan Province, China.

Suzi Eszterhas / Buff-cheeked gibbon (Nomascus gabriellae). Native to Asia. Captive.

Suzi Eszterhas / Buff-cheeked gibbon (Nomascus gabriellae) looking out from behind tree trunk. Native to Asia. Captive.

Ernie Janes / Yellow-cheeked gibbon (Nomascus gabriellae) female, close up of foot against glass. Captive, occurs in Vietnam, Laos, and Cambodia

Magnus Lundgren / Wild Wonders of China / Central Yunnan black crested gibbon (Nomascus concolor jingdongensis) moving through trees, silhouetted. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Magnus Lundgren / Wild Wonders of China / Central Yunnan black crested gibbon (Nomascus concolor jingdongensis), dominant male vocalising. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Magnus Lundgren / Wild Wonders of China / Central Yunnan black crested gibbon (Nomascus concolor jingdongensis), alpha male feeding on juvenile squirrel whilst sitting in tree. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Magnus Lundgren / Wild Wonders of China / Central Yunnan black crested gibbon (Nomascus concolor jingdongensis), alpha male feeding on juvenile squirrel whilst sitting in tree. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Magnus Lundgren / Wild Wonders of China / Central Yunnan black crested gibbon (Nomascus concolor jingdongensis), alpha male feeding on juvenile squirrel whilst sitting in tree. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Magnus Lundgren / Wild Wonders of China / Central Yunnan black crested gibbon (Nomascus concolor jingdongensis), alpha male feeding on juvenile squirrel whilst sitting in tree. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Magnus Lundgren / Wild Wonders of China / Central Yunnan black crested gibbon (Nomascus concolor jingdongensis), alpha male feeding on juvenile squirrel whilst sitting in tree. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Magnus Lundgren / Wild Wonders of China / Central Yunnan black crested gibbon (Nomascus concolor jingdongensis), alpha male feeding on juvenile squirrel whilst sitting in tree. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Magnus Lundgren / Wild Wonders of China / Central Yunnan black crested gibbon (Nomascus concolor jingdongensis), alpha male sitting in tree. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Magnus Lundgren / Wild Wonders of China / Central Yunnan black crested gibbon (Nomascus concolor jingdongensis), alpha male hanging from tree. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Magnus Lundgren / Wild Wonders of China / Central Yunnan black crested gibbon (Nomascus concolor jingdongensis), alpha male lounging in tree. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Magnus Lundgren / Wild Wonders of China / Central Yunnan black crested gibbon (Nomascus concolor jingdongensis), alpha male lounging in tree. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Magnus Lundgren / Wild Wonders of China / Central Yunnan black crested gibbon (Nomascus concolor jingdongensis), alpha male sitting in tree branch. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Magnus Lundgren / Wild Wonders of China / Central Yunnan black crested gibbon (Nomascus concolor jingdongensis), dominant male sitting in fork of tree. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Magnus Lundgren / Wild Wonders of China / Central Yunnan black crested gibbon (Nomascus concolor jingdongensis), mother and baby sitting in tree. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Magnus Lundgren / Wild Wonders of China / Central Yunnan black crested gibbon (Nomascus concolor jingdongensis), mother and baby surrounded by leaves in tree. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Magnus Lundgren / Wild Wonders of China / Central Yunnan black crested gibbon (Nomascus concolor jingdongensis), mother and baby swinging in canopy. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Magnus Lundgren / Wild Wonders of China / Central Yunnan black crested gibbon (Nomascus concolor jingdongensis), male sitting in tree, holding on to branch above. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Magnus Lundgren / Wild Wonders of China / Central Yunnan black crested gibbon (Nomascus concolor jingdongensis), juvenile male sitting in tree. Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

Magnus Lundgren / Wild Wonders of China / Information stone by roadside painted with gibbons and Chinese letters. Near ranger station, Wuliangshan Nature Reserve, Jingdong, Yunnan Province, China.

E.J. Peiker/ BIA / Wood Thrush (Hylocichla mustelina), Texas

Alan Murphy / Wood Thrush (Hylocichla mustelina), Texas

Dong Lei / Black crested gibbon (Nomascus concolor) male hanging and feeding, Wuliang Mountain National Nature Reserve, Jingdong county, Yunnan Province, China, Asia

Dong Lei / Black crested gibbon (Nomascus concolor) female with baby, Wuliang Mountain National Nature Reserve, Jingdong county, Yunnan Province, China, Asia

Dong Lei / Black crested gibbon (Nomascus concolor) female, with male and female behind, Wuliang Mountain National Nature Reserve, Jingdong county, Yunnan Province, China, Asia

Dong Lei / Black crested gibbon (Nomascus concolor) male climbing, Wuliang Mountain National Nature Reserve, Jingdong county, Yunnan Province, China, Asia

XI ZHINONG / West Yunnan black-crested gibbon (Nomascus concolor furvogaster) climbing, Yunnan, China, February.

XI ZHINONG / West Yunnan black-crested gibbon (Nomascus concolor furvogaster) climbing, Yunnan, China, February.

Robert Royse / Wood Thrush (Hylocichla mustelina), Ohio

Alan Murphy / Wood Thrush (Hylocichla mustelina), Texas

Alan Murphy / Wood Thrush (Hylocichla mustelina), Texas

Rod Williams / Young female Northern White-cheeked Crested Gibbon (Nomascus leucogenys) Northern Vietnam. Critically Endangered. Captive

Rod Williams / Male Northern White-cheeked Crested Gibbon (Nomascus leucogenys) Part of female visible top right, Northern Vietnam. Critically Endangered. Captive

Eric Baccega / Yellow / Golden cheeked crested gibbon {Hylobates / Nomascus gabriellae} Young male hanging in tree, captive, from Asia, IUCN Vulnerable

Eric Baccega / Yellow / Golden cheeked crested gibbon {Hylobates / Nomascus gabriellae} Young male hanging upside-down in tree, captive, from Asia, IUCN Vulnerable

Eric Baccega / Yellow / Golden cheeked crested gibbon {Hylobates / Nomascus gabriellae} Young male hanging in tree, captive, from Asia, IUCN Vulnerable

Eric Baccega / Yellow / Golden cheeked crested gibbon {Hylobates / Nomascus gabriellae} Young male hanging upside-down in tree, captive, from Asia, IUCN Vulnerable

Eric Baccega / Yellow / Golden cheeked crested gibbon {Hylobates / Nomascus gabriellae} mother and baby, captive, from SE Asia, IUCN Vulnerable

Tom Vezo / Wood Thrush (Hylocichla mustelinus), Rio Grande Valley, Texas

Tom Vezo / Wood Thrush (Hylocichla mustelinus), Rio Grande Valley, Texas

Dave Watts / Female Crested black / Concolor gibbon {Hylobates concolor} standing up on hind legs. Endangered species native to the forests of South China to Vietnam.

Roland Seitre / Southern white-cheeked gibbon (Nomascus siki) on branch. Captive, occurs in Lao People's Democratic Republic and Vietnam. Endangered species.

Joel Sartore / Photo Ark / Northern white-cheeked gibbon (Nomascus leucogenys) juvenile, critically endangered, clinging onto its surrogate mother, an endangered Lar gibbon (Hylobates lar) female, Omaha's Henry Doorly Zoo and A...

Joel Sartore / Photo Ark / Northern white-cheeked gibbon (Nomascus leucogenys) juvenile, with arms raised, portrait, Omaha's Henry Doorly Zoo and Aquarium, Nebraska. Captive, occurs in Southeast Asia. Critically endangered.

Joel Sartore / Photo Ark / Yellow-cheeked gibbon (Nomascus gabriellae) female, head portrait, Singapore Zoo. Captive, occurs in Southeast Asia. Endangered.

Joel Sartore / Photo Ark / Northern white-cheeked gibbon (Nomascus leucogenys) juvenile, portrait, Omaha's Henry Doorly Zoo and Aquarium, Nebraska. Captive, occurs in Southeast Asia. Critically endangered.

Joel Sartore / Photo Ark / Southern yellow cheeked gibbon (Nomascus gabriellae) male, head portrait, Singapore Zoo. Captive, occurs in Southeast Asia. Endangered.

Joel Sartore / Photo Ark / Northern white-cheeked gibbon (Nomascus leucogenys) female, portrait, Endangered Primate Rescue Center, Cuc Phuong National Park, Vietnam. Captive. Critically endangered.

Joel Sartore / Photo Ark / Northern white-cheeked gibbon (Nomascus leucogenys) female, with foot raised to its mouth, portrait, Endangered Primate Rescue Center, Cuc Phuong National Park, Vietnam. Captive. Critically endangered...

Joel Sartore / Photo Ark / Southern yellow-cheeked gibbon (Nomascus gabriellae) female, head portrait, Endangered Primate Rescue Center, Cuc Phuong National Park, Vietnam. Captive. Endangered.

Joel Sartore / Photo Ark / Northern white-cheeked gibbon (Nomascus leucogenys) female, head portrait, Gibbon Conservation Center, California. Captive, occurs in Southeast Asia. Critically endangered.

Joel Sartore / Photo Ark / Northern yellow-cheeked gibbon (Nomascus annamensis) male, portrait, Endangered Primate Rescue Center, Vietnam. Captive. Endangered.

Joel Sartore / Photo Ark / Southern white-cheeked gibbon (Nomascus siki) male, head portrait, Endangered Primate Rescue Center, Vietnam. Captive. Endangered.

Joel Sartore / Photo Ark / Northern white cheeked gibbon (Nomascus leucogenys) juvenile lying down whilst looking around, Omaha Zoo. Critically Endangered. Captive.

Doug Gimesy / Portrait of a female White-cheeked gibbon (Nomascus leucogenys). Adelaide Zoo, Adelaide, South Australia, Australia. April, 2015 PR supplied

Doug Gimesy / Portrait of a female White-cheeked gibbon (Nomascus leucogenys) in a tree. Adelaide Zoo, Adelaide, South Australia, Australia. April, 2015 PR supplied

Doug Gimesy / White-cheeked gibbon (Nomascus leucogenys) female and her adolescent daughter who is transitioning from grey to black. Adelaide Zoo, Adelaide, South Australia, Australia. PR supplied.

Staffan Widstrand / Wild Wonders of China / Northern white-cheeked gibbon (Nomascus leucogenys), adult male, Xishuangbanna National Park, Yunnan, China. Critically endangered.

Staffan Widstrand / Wild Wonders of China / Northern white-cheeked gibbon (Nomascus leucogenys), adult male, Xishuangbanna National Park, Yunnan, China. Critically endangered.

Doug Gimesy / White-cheeked gibbon (Nomascus leucogenys) female and two offspring, a male and female, sitting in tree. White-cheeked gibbons are sexually dimorphic with females having golden fur. Babies are born go...