Bearded Capuchin Monkeys Hunt More When Fruit Is Scarce, Study Finds

When fruit becomes scarce, wild bearded capuchin monkeys in Brazil switch from foraging to hunting small animals, a new long-term field study finds. The behaviour may offer clues to how early human ancestors obtained nutrient-rich food during shortages, before hunting large animals became common.

Researchers Susana Carvalho of Gorongosa National Park, Mozambique, Noemi Spagnoletti of Sapienza University of Rome, and colleagues followed two groups of wild bearded capuchins at Fazenda Boa Vista in northeastern Brazil. Published in the open-access journal PLOS ONE, the study drew on more than 5,000 hours of observation across 45 months, from 2006 to 2010, during which the team recorded 446 occasions of capuchins eating vertebrates -- animals with a backbone. Lizards made up 43% of the prey and rodents 28%, with opossums, iguanas and bird nestlings documented for the first time, alongside geckos, snakes, bats and birds.

Hunting increased as fruit availability declined, supporting the idea that vertebrates become worth the effort when food is scarce. One group received supplemental nuts, corn and water during the dry season; the group without this extra food hunted vertebrates at nearly twice the rate. Males ate vertebrates about 1.4 times as often as females and were more likely to pursue dangerous prey -- only males were observed eating snakes. Infants ate vertebrates at only one-fifth the adult rate, while juveniles did not differ significantly from adults, suggesting hunting skill develops with strength and experience.

The capuchins often ate the brain or internal organs first -- tissues rich in fat and nutrients -- before other parts such as eyes, skin, tails or paws, depending on the animal. Fossil sites dating back roughly 2 million years show that early members of the human lineage exploited small animals before large prey became a major resource. Humans remain the only living primates that regularly pursue animals as large as or larger than themselves, a behaviour known as the human predatory pattern.