- A viral video shows a family of Visayan warty pigs (Sus cebifrons) using a piece of tree bark or branch to build a nest at a zoo in Paris.
- Tool use has been widely reported among vertebrates, particularly primates, but this is the first published study and first recorded video of pigs using tools.
- The study suggests that using a stick is a socially learned behavior, and expands the possibility of tool use and social learning among pig species.
- There are limited studies on the Visayan warty pig, a critically endangered species in its native Philippines, due to its dwindling population in the wild.
PARIS — Priscilla grabs a piece of tree bark and uses it to dig the dirt in front of her. It’s classic tool use, the kind of thing primates are known to do, and it wouldn’t be remarkable, except that Priscilla is a female Visayan warty pig (Sus cebifrons), an endemic and critically endangered species in the Philippines famous for the Mohawk-like tuft of hair on its head and back. Now it’s got a new claim to fame: a penchant for using tools, according to a recent study.
The study by Meredith Root-Bernstein, Trupthi Narayan, Lucile Cornier and Aude Bourgeois stems from a video they shot and that went viral of Priscilla and her family digging a nest with a tree branch, a behavior not commonly observed and recorded among pigs. The video was taken at the Ménagerie at the Jardin des Plantes in Paris, which holds several types of endangered species.
“What is so exciting about pigs using tools? Pigs have long been maligned in many cultures and used as symbols of dirt, sloth, and avarice,” Root-Bernstein wrote in an email to Mongabay. “Even animal behavior researchers are not too interested in pigs despite recognizing their intelligence.”
The study, published in the journal Mammalian Biology last month, details how a family of Visayan warty pigs uses tools during the nest-building process, after Root-Bernstein “observed that the same piece of bark originally used as a digging tool remained visible [but] … the piece of bark was observed at different positions within the enclosure, always lying next to a recently created nest pit” in 2015.
The researchers returned to the Ménagerie during nesting seasons in October 2016 and 2017 to observe the family of four warty pigs, which were seen digging, rooting and even “moonwalking” — a backward shuffle in which they drag their feet to pile dirt, leaves and mulch into a mound around their nest, and reminiscent of Michael Jackson’s popular dance move.
Priscilla, the innovator of digging with a stick, isn’t the only one capable of manipulating a tool. Her mate, Billie, and their offspring, Beatrice and Antonia, mimicked her with varying results, the researchers observed. The female pigs used the sticks in a rowing motion while Billie attempted to use the stick but wasn’t as prolific. “When used by the females, it altered their digging affordance, and had a speciﬁc placement in the nest-building sequence,” the study says.
Billie, however, was always the first to initiate moonwalking. Indeed, his hands-on involvement in the entire nesting process was unexpected. “Since it is reported that adult male Sus cebifrons do not normally participate in nest building despite living year-round with females it is surprising that the adult male Billie performed aspects of the tool use behavior as well as participating in leaf collection, layering of leaves in the nest, and moonwalking,” the study says.
So how did the warty pigs learn to dig with tools? The study speculates the “excited head tossing” they perform when holding leaves or leafy branches at the beginning stages of nesting could be the origin of this behavior.
“Research on this species will help improve their welfare and care,” said Bourgeois, the head veterinarian at the Ménagerie. “Such a major finding is of primordial importance for increasing knowledge about this little known species and to raise awareness about the threats that face Visayan warty pigs and their habitats.”
Priscilla and Billie were born in captivity in 2007 and 2009, respectively. Their offspring, later named Antonia and Beatrice for the study, were born in 2012. The Ménagerie is part of a network of zoos under the European Endangered Species Program (EEP) that breeds Visayan warty pigs. There were 1,387 Visayan warty pigs across all EEP-associated zoos in 2015.
The species is endemic to six islands in the Visayas group of islands in the Philippines. But hunting for both meat and skin has driven the species to extinction in four islands. Remaining wild populations are limited to the islands of Panay and Negros.
Root-Bernstein, M., Narayan, T., Cornier, L., & Bourgeois, A. (2019). Context-specific tool use by Sus cebifrons. Mammalian Biology, 98, 102-110. doi:10.1016/j.mambio.2019.08.003
Banner image of a Visayan warty pig (Sus cebifrons) in Plackendael zoo in Belgium, a part of the European Endangered Species Program (EEP). Image by Ad Meskens / Wikimedia Commons [CC BY-SA 4.0]
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