When Fruit Is Scarce, These Monkeys Hunt Animals. The Behavior May Offer Clues About the Origins of Humans’ Meat-Eating Habits

The bearded capuchins of northeastern Brazil typically eat plant-based foods, but they turn to small vertebrates when those sources are limited. Our ancestors may have done the same, eventually allowing predatory behaviors to be more frequently passed on in our lineage

Sarah Kuta | Daily Correspondent

August 28, 2026 10:00 a.m.

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The bearded capuchin monkeys of northeastern Brazil eat a mostly plant-based diet, chowing down on palm nuts and other fruits. But when plant foods are scarce, the primates consume a surprisingly diverse smorgasbord of small animals, including snakes, opossums, iguanas, bats, rodents and bird eggs and nestlings, researchers report in a study published on August 26 in the journal PLOS One.

The findings reveal new details about the diet and behavior of these highly adaptable, long-lived monkeys. But they could also shed light on the evolution of human diets, including our ancestors’ shift toward eating more meat.

Hunting small prey seems to help capuchins cope with seasonal fluctuations in plant food availability—and “this may have also been the case for hominins,” study co-author Susana Carvalho, a primatologist at Gorongosa National Park in Mozambique, tells Science News’ Jake Buehler.

When the researchers started studying wild capuchins in the privately owned area of Fazenda Boa Vista roughly two decades ago, they primarily wanted to investigate the monkeys’ tool use and other complex behaviors. But while following two groups of the primates, scientists noticed that they were actively hunting and consuming small backbone-bearing creatures, or vertebrates—an intriguing behavior for a species that usually eats fruit. So, the researchers began making detailed notes whenever they saw the monkeys going after animals.

They ended up with more than 5,000 hours of observations between May 2006 and December 2010, recording 446 instances of capuchins eating animals. The team also looked at factors that may have affected the animals’ diets, including the age and sex of the individual monkeys that were chowing down on vertebrates, rainfall, temperature, humidity and the relative abundance of fruits and insects at the time.

The overlaps revealed some clear patterns. When plant foods became scarcer due to seasonal fluctuations, the monkeys seemed to hunt more. Lizards and rodents made up most of their prey, but the monkeys hunted a wide variety of animals. Scientists spotted males and females of all ages feasting on small vertebrates, but the behavior was more common among adult and juvenile males.

And when their hunts were successful, the monkeys seemed to go for the brains and guts first, before eating the rest of the body.

“This may allow them to obtain energy-rich fats and other nutrients quickly, which could be especially advantageous when prey is likely to be taken by another group member,” says study co-author Noemi Spagnoletti, a conservation biologist at Sapienza University of Rome, in an interview shared by the journal.

Chimpanzees often get the limelight for eating vertebrates, but a range of nonhuman primates also engage in the behavior, Margaret Bryer, a biological anthropologist at the University of Wisconsin-Madison who was not involved in the study, tells Science News.

But while chimpanzees are some of our closest living relatives, bearded capuchins and humans are only distant cousins, and the creatures are not considered a direct model for our ancestors. However, the monkeys share enough similarities with humans that they might offer some clues about the evolution of early hominin behavior.

Humans are the only primates around today that regularly hunt animals larger than themselves—but how and why our ancestors evolved this behavior remains largely a mystery.

One hypothesis posits that our ancestors started eating smaller prey in times of seasonal plant food scarcity, before eventually leveling up to bigger game.

“As late Pliocene and early Pleistocene eastern African hominin environments became increasingly seasonally arid, the availability of plant-source foods that are key to many primates’ diet in forest habitats would have only been available intermittently, whereas animal resources would have remained accessible throughout the year,” the researchers write in the paper. “This may have selected for a higher frequency of predatory behaviors in our lineage.”

The new findings seem to support this possible explanation, suggesting that hunting small animals might have been a “stepping stone to the exploitation of larger prey” for humans, Carvalho says in a statement.

“The fossil record now needs re-analyzing to look at evidence of small vertebrate predation” by early humans, she adds.

Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.