Primates studied included the black and gold howler monkey, tufted capuchin, black-capped squirrel monkey, and Peruvian spider monkey. Monkeys, scientists found, had a secret yodelling weapon ...

In this study we wanted to assess the responses of two groups of tufted capuchin monkeys (N=11) to a 30 cm x 25 cm feeding board. The board consisted of a metal support to which plastic blades of ...