A 'purring' monkey (Callicebus caquetensis) – Colombian Amazon The new species, named the Caqueta titi monkey or Callicebus caquetensis, is one of about 20 species of titi monkeys, which all live in the Amazon basin. The population size has been estimated at less than 250 individuals, and its habitat has been fragmented by clearing for agricultural land. It is classified as critically endangered by the IUCN. According to scientists, titi monkeys are among the few species of primates that are monogamous. 'All of the babies purr like cats too,' said Thomas Defler, who was part of the team that discovered the species. 'When they feel very content they purr towards each other, and the ones we raised would purr to us'

Photograph: Thomas Defler/WWF