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.

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

Roland Seitre / Lemurine Night Monkey (Aotus lemurinus) captive at Parque Jaime Duque, Sopo, Bogota, Cundinamarca, Colombia. Vulnerable species. Native to northern South America.

Roland Seitre / Bolivian Night Monkey (Aotus azarae boliviensis) portrait, captive. Native to Peru.

Roland Seitre / Andean Night Monkey (Aotus miconax) captive at Huachipa Zoo, Lima, Peru, vulnerable species. Endemic to Peru.

Roland Seitre / Black-headed Night Monkey (Aotus nigriceps) portrait of two in nest, captive. Native to Brazil, Peru, and Bolivia.

Roland Seitre / Northern Night Monkey (Aotus trivirgatus) climbing branch, in rainforest, Brazil.

Roland Seitre / Northern Night Monkey (Aotus trivirgatus) climbing down branch, Brazil.

Roland Seitre / Ma's Night Monkey (Aotus nancymaae) captive at Huachipa Zoological Park, Lima, Peru. Endemic to Peru and Amazonas in Brazil.

Roland Seitre / Grey-handed Night Monkey (Aotus griseimembra) captive in zoo, Pereira, Risaralda, Colombia. Vulnerable species. Native to Colombia and Central America.