Heaviest night monkey

As their name suggests, South America's night monkeys, or douroucoulis, are nocturnal – the world's only nocturnal monkeys. Of the 11 species currently recognized, the heaviest is Azara's night monkey Aotus azarae, which weighs approximately 1.25 kg, with males slightly heavier and longer too than females. It is also known as the southern night monkey, as its geographical range encompasses Peru, Brazil, Argentina, Paraguay and Bolivia.

Interestingly, despite its "night monkey" name and taxonomic affiliation to the other 10 species, Azara's night monkey is unique in that populations of this species existing in the Gran Chaco region are also active during daylight hours, and even at night it prefers bright moonlight in which to move around in the trees where it spends its entire life.