Capuchin Monkeys Hunt More Small Animals When Fruit Grows Scarce

Bearded capuchin monkeys in northeastern Brazil hunt and eat small vertebrates more often when fruit becomes scarce, researchers report August 26 in the journal PLOS One. The finding may offer clues to the diets of early human ancestors.

The study builds on long-term fieldwork on bearded capuchins (Sapajus libidinosus) led by Noemi Spagnoletti, a zoologist at Sapienza University of Rome. "We repeatedly observed the monkeys actively hunting and consuming vertebrates, including lizards, snakes and iguanas," Spagnoletti says. She and her colleagues analyzed data from more than 5,000 hours logged between June 2006 and December 2010, comparing the monkeys' diet with plant food availability.

Researchers recorded 281 instances of the capuchins eating small vertebrates. Nearly half were lizards and over a quarter were rodents, with birds and opossums making up the rest. As fruit became less common during seasonal shifts, the monkeys hunted and ate more vertebrates, often eating the brains and guts first. Spagnoletti says eating vertebrates may be worth the extra hunting effort in scarce times, since the fats and nutrients in brains and organs could be a quick way to meet dietary needs.

Chimpanzees get the most attention for hunting vertebrates, but many nonhuman primates eat them too, including capuchins, says Margaret Bryer, a biological anthropologist at the University of Wisconsin-Madison who was not involved in the study. Susana Carvalho, a primatologist at Gorongosa National Park in Mozambique, notes that bearded capuchins and humans share traits such as large brains, meat-eating, and tool use carried while walking upright; unlike chimpanzees, capuchins also eat snakes. "Meat may be important to buffer seasonal changes" for the monkeys, Carvalho says, and "this may have also been the case for hominins."

Carvalho says future work should examine whether hunting small vertebrates was a stepping stone toward humans' eventual pursuit of big game, and that the finding opens a new window to revisit the fossil record for evidence of smaller prey species.