Scientists watched in amazement as screams sounded from the treetops just before a baby monkey fell to its death. Just moments later, the baby’s monkey family gathered around to consume the corpse.

Researchers have been observing this population of white-faced capuchin monkeys (Cebus imitator) for over 37 years. But in all that time, scientists had never recorded a case of cannibalism.

In October 2020, the research team described the unusual incident in the journal Ecology and Evolution.

A 10-day-old monkey, known as CT-19, fell to the ground after loud screams came from the treetops. The monkey’s mother, called CT, crawled down to her child. CT tried to carry the baby back into the treetops, but the infant fell both times. Other monkeys soon gathered around to inspect the corpse.

A 2-year-old male monkey approached the lifeless body and started nibbling at the dead monkey’s foot. “Though CT made no attempt to retrieve the corpse, she remained close by and vigilant,” the researchers said. An alpha female, age 23, then took the corpse away from the young male and gnawed at the corpse. After half an hour, the female had consumed the infant’s entire lower half, leaving only the head, chest and arms.

Before this case, only eight cases of cannibalism in primates has been observed in all of Central and South America. Cannibalism in primates is rare, and usually coincides with infanticide committed by unrelated adults.

In this case, there is reason to believe that CT-19 was a victim of infanticide, the researchers said.

White-faced capuchin monkeys usually eat both plants and small animals, such as lizards, squirrels, and birds. When they capture animal prey, the monkeys usually began their feast by biting the face, in order to quickly silence the animal and to avoid being bitten themselves. The capuchins usually consume the entire animal, either alone or as a group. When cannibalizing one of their own, however, the monkeys behaved quite differently; only two monkeys took part in the meal and they left the entire upper half of the corpse untouched.

The researchers believe that the couple monkeys that did turn to canibalism did so far for nutritional benefit. About two weeks after the incident, the alpha female gave birth to her own young. This means she was in the late stages of pregnancy at the time. The young male had recently been weaned from his own mother when he ate the baby monkey.

This suggests that capuchins may resort to cannibalism when they are in desperate need of supplemental nutrients.