Female monkeys may shout during sex to help their male partners climax, research now reveals.

Without these yells, male Barbary macaques (Macaca sylvanus) almost never ejaculated, scientists found.

Female monkeys often utter loud, distinctive calls before, during or after sex. Their exact function, if any, has remained heavily debated.

To investigate the purpose behind these calls, scientists at the German Primate Center in Göttingen focused on Barbary macaques for two years in a nature reserve in Gibraltar.

The researchers found that females yelled during 86 percent of all sexual encounters. When females shouted, males ejaculated 59 percent of the time. However, when females did not holler, males ejaculated less than 2 percent of the time.

To see if yelling resulted from how vigorous the sex was, the scientists counted the number of pelvic thrusts males gave and timed when they happened. They found when shouting occurred, thrusting increased. In other words, hollering led to more vigorous sex