A capuchin named Joker started the apparent trend, leading researchers to suspect "there was something a little quirky about him, or that he was kind of lonely in a way.”

Scientists have captured footage of an unusual social tradition in capuchin monkeys abducting infant howler monkeys – a never-before-seen behaviour in wild primates. At such a critical moment in US history, we need reporters on the ground. Your donation allows us to keep sending journalists to speak to both sides of the story.