Pigs may never fly, but they’re capable of using tools, as fascinating new research demonstrates.
Chimps, elephants, dolphins, otters, crows, and, of course, humans, are among the few creatures on Earth known to use tools. We can now add pigs to this exclusive list, thanks to new research published this week in Mammalian biology.
Over the course of three years, a team led by biologist Meredith Root-Bernstein from the Institute of Ecology and Biodiversity in Chile and the French National Institute for Agricultural Research observed multiple instances of tool use in Visayan warty pigs (Sus cebifrons), in which the animals used sticks and bark to dig nests in their zoo enclosures. Among pigs, this behaviour is rare and likely not instinctual, according to the researchers, which means the tool use is the result of adaptive intelligence and social learning, highlighting previously under-appreciated aspects of pig intelligence.
Pigs are renowned for their smarts, so it’s fair to ask why this behaviour hasn’t been spotted until now – a question we posed to Root-Bernstein.
“Who knows!” she wrote in an email to Gizmodo. “I was very surprised when I realised that there were no previous reports of tool use in pigs. Pigs are smart, playful, social, and like to manipulate objects, and they are omnivores so they naturally have to process lots of different kinds of edible objects – all conditions that often are associated with tool use in other animals. Maybe people just haven’t been paying attention enough. Or, people may have observed different kinds of pigs using tools but scientists just didn’t hear about it.”
The current study was prompted by an accidental observation made by one of the researchers at the Ménagerie of the Jardin des Plantes in Paris, France (a zoo for endangered species), who caught a Visayan warty pig in the apparent act of using tools. This fortuitous observation motivated the scientists to conduct a formal investigation into the matter, which they did through a series of experiments running from 2015 to 2017.
A warty pig gathering leaves for its nest. Image: M. Root-Bernstein et al., 2019
Root-Bernstein said little is known about the natural behaviour of Visayan warty pigs, an endangered species from the Philippines. They live in family groups and spend their days combing the forest floor for various food sources. Female warty pigs make nests by digging a hole and lining it with leaves, which they do to care for their piglets. Importantly, the tool use observed in the current study happened in the context of building these nests, said Root-Bernstein.
For the analysis, the scientists chose a definition of tool use devised by scientists Robert St. Amant and Thomas Horton from North Carolina State University, who described tool use as “the exertion of control over a freely manipulable external object (the tool) with the goal of (1) altering the physical properties of another object, substance, surface or medium... via a dynamic mechanical interaction, or (2) mediating the flow of information.”
Video stills shows Priscilla using a piece of bark to dig a hole. Image: M. Root-Bernstein et al., 2019
Four different pigs were included in the study, all of which were born into captivity. The pigs included Priscilla, a female born in 2007; Billie, a male born in 2009; and their unnamed female offspring, both born in 2012 (and later named Antonia and Beatrice to avoid conflating the two). Over the course of the study, the researchers catalogued 11 instances over the three years in which the pigs used tools, specifically bark and sticks, to assist with their nest building. The pigs used these items like a shovel, moving them back and forth to produce a discernible digging action. All pigs were observed to use tools, including Billie.
In experiments conducted in 2015, the researchers thought that the addition of more leaves in the enclosure might stimulate tool use, but that didn’t work. In 2016, the scientists simply watched the pigs without interfering, during which time tool use emerged spontaneously. In experiments run in 2017, the researchers added a spatula to the mix to see if the pigs would go for it, but they didn’t.
Importantly, the tool use behaviour was unprompted.
“By unprompted, we meant that we didn’t set up a situation in which there was a problem to solve and a tool that could be used to solve it with, like would happen in a controlled experiment,” explained Root-Bernstein.
The researchers also documented an odd behaviour they called “moonwalking,” which happened while the pigs built their nest.
“It was the behaviour that always preceded tool use in the nest-building steps,” said Root-Bernstein. “The pigs really looked like they were imitating the move by Michael Jackson – they did it to push soil backwards to form the walls of the nest. The pigs were quite playful and had distinct personalities, we often laughed about them while carrying out the observations.”
More seriously, the new research expands our understanding of social learning in pigs. Pigs, as previous research has shown, are capable of learning from one another about things like where to find food and figuring out which foods are good to eat. Wild boars, in another example, have been observed to wash foods, which they likely learned from each other, said Root-Bernstein.
“We suggest that the Visayan warty pigs in our study probably learned the behaviour from the mother, Priscilla, who may have invented it, because she does it most. But we are just speculating based on known patterns of social learning in other species,” she said. “It would be nice if someone would do some more sophisticated studies of social learning in pigs.”
Given their intelligence, Root-Bernstein said she’d be surprised if pigs can’t learn more than just where to find food, and she suspects pigs can learn actions and possibly even goals from one another.
Featured image: M. Root-Bernstein et al., 2019