Thomas Marent / Black-headed Night Monkey (Aotus nigriceps) at night, Tambopata-Candamo Nature Reserve, Peru

Rod Williams / Night monkey {Aotus trivirgatus} juvenile, captive, from Central and South America

Lucas Bustamante / Spix's night monkeys (Aotus vociferans) in a tree hole, Yasuni National Park, Orellana, Ecuador

Lucas Bustamante / Three Spix's night monkeys (Aotus vociferans) looking out of a hole in a tree trunk, Cuyabeno National Park, Sucumbios, Ecuador.

Sean Crane / Panamanian Night Monkey (Aotus zonalis) in tree cavity, Soberania National Park, Panama

Thomas Marent / Gray-handed Night Monkey (Aotus griseimembra) trio in tree cavity, Magdalena Valley, Colombia

Thomas Marent / Gray-handed Night Monkey (Aotus griseimembra) trio in tree cavity, Magdalena Valley, Colombia

Cyril Ruoso / Douroucouli (Aotus nigriceps) three in tree nest, Pacaya Samiria National Park, Amazon, Peru

Cyril Ruoso / Douroucouli (Aotus nigriceps) Pacaya Samiria National Park, Amazon, Peru

Thomas Marent / Black-headed Night Monkey (Aotus nigriceps) scratching itself at night, Tambopata-Candamo Nature Reserve, Peru

Thomas Marent / Black-headed Night Monkey (Aotus nigriceps) at night, Tambopata-Candamo Nature Reserve, Peru

Thomas Marent / Black-headed Night Monkey (Aotus nigriceps) group at night, Tambopata-Candamo Nature Reserve, Peru