Zoologists observed capuchin monkeys hunting a chicken for 20 minutes.

The diet of primates is as variable as the diversity of these mammals. Their eating habits are not well studied—recently, Naked Science reported that primatologists discovered deer truffles in the diet of western lowland gorillas. However, it is known that orangutans, for example, prefer fruits, bonobos add stems and leaves of shrubs to their diet, while chimpanzees are omnivorous: they consume not only sweet fruits and insects but also the meat of birds or smaller monkeys.

As for the diet of spider monkeys (Atelidae) or saki monkeys (Pitheciidae), it can be described as flexible. In addition to their primary plant-based food, they sometimes eat meat—hunting various vertebrates, primarily done by males. Capuchins, by the way, are among the most carnivorous non-ape primates. This flexibility allows some populations to survive during unfavorable seasons or in areas where their natural habitat is rapidly declining.

Recently, two Brazilian zoologists observed unusual hunting behavior among capuchins living in the city of Foz do Iguaçu in southern Brazil. The researchers have been monitoring the local population since 2011, with systematic studies of the semi-wild group conducted from January to September 2019. The group consisted of 20 capuchins—two adult males, four adult females, and other individuals of various ages. The specialists were able to determine only the genus of the observed primates (Sapajus)—the color of their fur and facial features allowed them to classify them as either Sapajus cay or brown capuchins (Sapajus nigritus). A detailed description of this rare hunting behavior was published in the journal Primates.

Local Brazilians sometimes raise chickens—the researchers have encountered such farms since 2011. On January 9, 2019, during the day, an adult male capuchin named "Alemão" descended from the tree where he had been resting and began to chase a domestic chicken. After three minutes, he caught it by the neck, and at that moment, another capuchin joined him. Together, they grimaced and yelled towards the other group members, plucking at their catch, but the chicken managed to escape.

The capuchins dragged the chicken to the trees, tossing it into the air and hitting it against the ground and roots. At that point, "Alemão" bit the chicken, after which it calmed down and, apparently, died. Other monkeys began to approach the hunters. While one capuchin was plucking the chicken, "Alemão" ate its eyes and chewed on other parts of its head. Then the group members also started biting the carcass, occasionally tossing the prey and dropping it on the ground—some nibbled on parts of the legs, while others took bites from the neck.

The entire hunt lasted 22 minutes, after which the monkeys left the dead bird alone and departed. The researchers noted that the chicken was quite a substantial catch for the capuchins, as it weighed about half that of an adult male. Such an occurrence is rather rare, especially for New World monkeys (Platyrrhini). Among them, only howler monkeys have been known to eat chicken eggs.

The studied group of capuchins, as the biologists suggested, did not acquire enemies among Brazilians due to this hunting behavior because locals raise chickens not for sale. It has also happened that people fed these monkeys—giving them cookies or bread—and sometimes capuchins rummaged through waste in search of food. New observations help evaluate potential food sources for capuchins and generally highlight atypical behavior for them.