Animals

In a colony, king penguins act like a liquid

These birds congregate during breeding season —but never too closely

Positions of king penguins in a breeding colony resemble molecules in a 2-D liquid, a new study finds.

Paul-Émile Victor/French Polar Institute

May 14, 2018 at 5:45 am

Emperor penguins huddle to keep warm. Certain others of their royal kin — king penguins — prefer more personal space. Even in big colonies, these birds will keep their distance. But here’s the new part. In such a setup, king penguins act like molecules in a liquid, physicists now conclude. Each acts as though it’s both attracted to and repelled by its neighbors.

Researchers can use aerial photos to see how closely penguins in a colony choose to space themselves. King penguins group together to breed. Yet not too close. No pair will be closer than a few meters (yards) from its neighbors.

When the birds are disrupted, they move about — only to once again settle into their original spacing. It’s a little like how water fills the space you took up when you climb out of the bathtub. This strange, liquid-like property of the colony was reported April 4 in the Journal of Physics D: Applied Physics.

Physicists use math to describe, or model, the motions and forces at work in the world. “Simple physics models are elegant and can explain a lot,” says Dan Zitterbart. An author of the study, he works at Woods Hole Oceanographic Institution in Massachusetts.

Unlike most birds, king penguins (Aptenodytes patagonicus) don’t make a nest. Instead, they cradle their eggs on top of their feet. This keeps the birds from being stuck in one place. They can shuffle around, to reposition themselves, much as a fluid can. For instance, when an elephant seal strolls up, the birds scoot out of its way. Once the seal is gone, the birds refill the space. This liquid-like behavior also depends on the birds’ habitat and attitude.

King penguins live on small islands in the South Atlantic. These islands afford the birds little room. This is the attractive force that pulls the penguins together. But the penguins also will peck at any neighbor who gets too close. This territorial instinct pushes the birds apart.

How penguins arrange themselves could clue researchers in to a colony’s health. If the birds are spread especially far apart, this might signal that their population has gotten really low. Keeping track of these birds is important, because climate change threatens some of their populations with extinction.