Pigs Use Mirrors

Smart swine can figure out how to find a bowl of food.

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By Susan Milius, Science News

Forget lipstick on a pig. The first report of pigs learning to use a mirror is about finding the food.

Give pigs a chance to experiment with a mirror first and most of them can find dinner based on only a food bowl’s reflection, says Donald Broom of the University of Cambridge in England, who studies animal cognition and welfare. Pigs that don’t have a chance to learn about mirrors first tend to poke around behind the mirror, Broom and his colleagues report in an upcoming issue of Animal Behaviour.

Broom says the findings suggest that pigs have what he considers a relatively higher degree of awareness. In what he terms “assessment awareness,” an animal marshals observations and memories to evaluate a situation in relation to itself over a short span of time and demonstrates this awareness with appropriate action.

When he first let pigs explore a mirror, the animals approached in stages, often ending up with nose pressed against glass. One pig actually broke the mirror after charging as if it were a rival. Pigs looked behind the mirror, and often watched it as they moved in front of it.

For the test, Broom and his colleagues gave four pairs of pigs five hours to check out a mirror in a pen. Then each pig was penned with a mirror that was angled so it reflected a bowl of apple slices or M&M’s on the other side of a partition. When researchers let the test pigs free to snuffle around the area, seven of the animals went behind the partition and found the food. Most pigs in a control group that had never seen a mirror before poked around behind the mirror, as if they were searching for food there.

“It is nice to have this data point, but it has already been demonstrated in other animals,” says Marc Hauser, who directs the Cognitive Evolution Lab at Harvard University. “The paradox is why animals that can use a mirror to find hidden objects can’t use it to recognize themselves.”

For a mirror test of self-recognition, researchers often put some kind of dye or mark on an animal and then look to see if the animal pokes at the marked spot on its body after catching a glimpse of the spot in the mirror. Researchers have reported clear positive results from very few nonhuman animals—magpies, bottlenosed dolphins, elephants and apes.

Broom says he has tried marking pigs before letting them look at a mirror, but that the result didn’t tell him much. Pigs didn’t pay attention to the marks, but “this is not surprising considering how often they get marks on themselves,” he says.

The recognition that pigs have at least some degree of awareness may earn them better treatment, Broom says. Now “conditions for meat-production pigs often do not meet their needs; densities are very high,” he says. “If an animal is clever, it is less likely to be treated as if it is an object or a machine to produce food.”