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If you ever find yourself in fisticuffs with a Magellanic penguin, you’ll want to block right. A recent study found that during fights, the pluckiest penguins in Argentina’s Punta Tombo colony were lefties. The finding is the first evidence of side dominance—also known as lateralization—in a wild population of flightless birds.
A team of researchers led by Thaís Stor, a graduate student at Brazil’s Federal University of Pernambuco, used a number of tests to see if their tuxedoed subjects had a dominant side. They looked for signs of footedness by watching when the birds stepped onto an obstacle or stretched a leg to cool off. They also looked for uneven wear on the flipper feathers as a sign of a bird’s preference for turning one way underwater, which would indicate “flipperedness.”
“The penguins show evidence of having a dominant flipper,” explains Ginger Rebstock, a researcher at the University of Washington and coauthor of the paper, adding that about half preferred turning left and half preferred turning right. Foot tests produced a similarly split result, but something interesting happened when the birds got rowdy.
Penguin fights tend to occur out of sight in deep burrows, but lasting facial injuries leave clues about each exchange. During aggressive encounters, around 70 percent of penguins showed lefty tendencies, bloodying the right side of an opponent. “They hit, they bite, they peck,” explains Rebstock, who has personal experience with such encounters. “These penguins can do some damage. I’ve been whacked. It hurts!”
That penguins have a seek-and-destroy side preference was of particular interest to the team. Side dominance happens when the brain assigns specific tasks to different hemispheres—an ability long thought to be exclusive to humans. “We’re finding, however, that pretty much every animal we study shows some sort of handedness,” says Rebstock.
The study also piqued the interest of Lesley Rogers, a neuroscientist and animal behavior researcher at the University of New England in Australia who helped prove the existence of lateralization in nonhuman animals in the 1970s.
“It was [erroneously] used as evidence of our superiority as a species,” says Rogers, who was not involved in the new research.
About 90 percent of people are right-handed. The right side of the body is controlled by the left hemisphere of the brain, and our ability to speak is similarly handled on the left. This asymmetry led scientists to believe that lateralization was the pinnacle of evolution, one that coincided with our development of complex language.
“Well, that’s gone by the board,” says Rogers with a laugh. “We now know that wherever a brain can perform different functions on one side and the other, it seems to do so.”
That makes sense: compartmentalizing the control center allows an organism to multitask more efficiently, react faster, and avoid confusion when the eyes get different inputs. Vertebrates from whales to chickens—and even invertebrates such as social bees—show some kind of lateralization. The way tasks are filed in the brains of those animals is also surprisingly consistent. Feeding, for example, is usually handled by the left hemisphere. Predator detection, the right.
Penguin battle behavior lines up, too. Penguins peck their opponent’s right sides because they use the left eye during fights. They likely attack with the left flipper for the same reason, and they’re not alone in the strategy. Feral stallions will also turn to view an interloper with the left eye before launching an attack. Gelada baboons are more reactive to those in their left field of view. And a study of impala pelts revealed scars are typically found on the right.
The new finding adds to a growing theory that aggression resides in the right half of the brain—something scientists are still working to understand. “I’m not surprised that they found it,” says Rogers. “But it’s a lovely, important example.”