The Douroucoulis, also called Night Monkeys and Owl Monkeys, as the name indicates, are active at night. They are native to jungles/forests of Central and South America.
The several species are divided into two groups, the red-necked, below, with ginger chest fur, and the grey-necked.
Above is the Bolivian subspecies of Azara's Night Monkey, Aotus azarai/azarae boliviensis.
Like other Night Monkeys, it lives in mainly monogamous pairs with the father taking on most parental care of offspring.
Apologies for poor pictures but I don't like to use flash on animals.
Above is the Black-headed Night Monkey, Aotus nigriceps, native to Bolivia, Peru, Colombia and Brazil.
Tame and encouraged to be active in daylight in a park in Peru.