The International Union for Conservation of Nature lists a dozen types of night monkeys on its Red List of threatened species. Though none is listed as endangered, several are suffering declining populations.
In Colombia, Brieva said, "Their natural habitats are being destroyed by the expansion of the agricultural frontier, by the indiscriminate cutting o the forests and jungle."
Silva says she has raised two other baby monkeys and both of those were freed in different parts of the country. She hasn't heard anything about them since.
"It is like with a child. You are at peace because they are going to be in their natural habitat," she said.