Recent sightings of swines using tools add to the evidence that humans are not the only intelligent and crafty animals around.
In the past, researchers used to think that the use of tools — using objects to either alter the environment, find or prepare food, or make other tools — was a human-specific trait, as it told of higher cognitive abilities.
However, over the years, it has become apparent that many other animals — and not just mammals — use tools to enhance their lives.
For example, many nonhuman primates, including chimpanzees, use tools to forage and access food sources to which it would otherwise be more difficult to gain access.
Corvids, such as the New Caledonian crow, can even combine different objects to form composite tools that allow them to retrieve food.
Researchers have also observed a species of marine fish called wrasses using rocks to crack open bivalves to gain access to their tasty flesh.
Now, researchers from the Université Paris-Saclay in Thiverval-Grignon and from UNESCO, the University of Paris, and the Muséum National d'Histoire Naturelle — all in Paris, France — report observing tool-using behaviors in a species of swine.
In a study paper that now appears in the journal Mammalian Biology, the investigators describe how Visayan warty pigs (Sus cebifrons) — primarily females — at the Ménagerie of the Jardin des Plantes in Paris were apparently using sticks and pieces of bark as tools in the process of constructing farrowing nests.
An incidental sighting at the zoo
In the wild, female Visayan warty pigs construct farrowing nests before they are due to give birth to their young. Like other species of swine, Visayan warty pigs have demonstrated that they are intelligent, and researchers have thought that they might be able to use tools.
However, to date, no one has reported actually seeing swine using tools for any given purpose.
"Pigs' extractive foraging, object manipulation, playfulness, and nest-building make them candidates for tool use, although their lack of digits or beaks allowing for a finely controlled grasp may limit their expression of such behavior," the researchers write in the study paper, adding that to their knowledge, "there is no literature on tool use in pigs."
This changed when one of the study authors, Meredith Root-Bernstein, happened to spy one of the Visayan warty pigs at the Ménagerie in Paris using a piece of bark to dig.
"She would deposit some leaves, move them to a different spot on the [nest] mound, and dig a bit with her nose. At one point, she picked up a flat piece of bark about 10 cm x 40 cm that was lying on the [nest] mound and, holding it in the middle in her mouth, used it to dig, lifting and pushing the soil backward quite energetically and rapidly. The digging motion was repeated six or eight times," Root-Bernstein reported.
This observation piqued her and her colleagues' interest. With the approval of the Ménagerie staff, they set out to observe the swine and see whether they could record the tool-using behavior again. They also hoped to determine what the Visayan warty pigs were using tools to achieve.
Females were skilled, the male not so much
At first, the team observed the Visayan warty pigs repeatedly at intervals throughout the year, believing that the tool-wielding might be part of their foraging efforts. However, this turned out not to be the case.
The team came up with another theory: Maybe the females used bark and twigs exclusively to create their nests. So the researchers set out to observe the animals again close to nest-building time, and, sure enough, they recorded them using bark and twigs as tools once more.
More specifically, the "matriarch" of the group — which the zoo staff had named Priscilla — and one of her daughters used sticks and pieces of barks on four different occasions to help them construct nests.
The one male in the enclosure, which the zoo staff call Billie, tried to imitate the females' use of a stick as a tool, but was unsuccessful.
Billie "picked up the stick and attempted a rather clumsy digging action" without much success, the authors note in the study paper.
Further experiments confirmed that the females' use of different objects as tools to help them complete nest construction was not a fluke as they did it again and again on different occasions. Billie, the male, reportedly tried to "help out," but his attempts were again doomed to failure.
The researchers write:
"We were able to confirm the original observation of instrumental object manipulation, implying that this was not a one-off event but a part of the pigs' behavioral repertoire. [...] The results of these observations suggest that instrumental object manipulation occurs within the behavioral sequence of nest-building."
Passing skills from mother to daughter
The investigators do admit that it is hard to say whether Visayan warty pigs and other species of swine use tools in nature or whether this is a behavior that the animals at the Paris zoo have developed while in captivity.
If the latter, they hypothesize that "the transmission of the behavior was either vertical, from mother to daughter, or horizontal, between adult females and to the adult male, Billie."
"It may be unlikely that Billie originated the innovation, since his observed attempted tool use during Study 2 was particularly inept," they add.
In any case, the researchers believe that the behaviors that they witnessed are clear proof of the fact that swine have, at the very least, the capacity to innovate by using natural objects as tools.
"Our observations open fertile new ground for research on tool use and social learning in [swine]," they conclude.
Below, you can watch the researchers' video recordings of the female Visayan warty pigs using bark and twigs as tools at the Ménagerie in Paris.