In a colony, king penguins act like a liquid | Science News for Students

In a colony, king penguins act like a liquid

These birds congregate during breeding season —but never too closely
May 14, 2018 — 6:45 am EST
penguin group

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

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.

Power Words

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aerial     Of or taking place in the air.

Atlantic     One of the world’s five oceans, it is second in size only to the Pacific. It separates Europe and Africa to the east from North and South America to the west.

behavior     The way something, often a person or other organism, acts towards others, or conducts itself.

birds     Warm-blooded animals with wings that first showed up during the time of the dinosaurs. Birds are jacketed in feathers and produce young from the eggs they deposit in some sort of nest. Most birds fly, but throughout history there have been the occasional species that don’t.

breed      (verb) To produce offspring through reproduction.

climate     The weather conditions that typically exist in one area, in general, or over a long period.

climate change     Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.

extinction     The permanent loss of a species, family or larger group of organisms.

force     Some outside influence that can change the motion of a body, hold bodies close to one another, or produce motion or stress in a stationary body.

habitat     The area or natural environment in which an animal or plant normally lives, such as a desert, coral reef or freshwater lake. A habitat can be home to thousands of different species.

kin     Family or relatives (sometimes even distant ones).

liquid     A material that flows freely but keeps a constant volume, like water or oil.

model     A simulation of a real-world event (usually using a computer) that has been developed to predict one or more likely outcomes. Or an individual that is meant to display how something would work in or look on others.

molecule     An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).

penguin     flightless black-and-white bird native to the far Southern Hemisphere, especially Antarctica and its nearby islands.

physicist     A scientist who studies the nature and properties of matter and energy.

physics     The scientific study of the nature and properties of matter and energy. Classical physics is an explanation of the nature and properties of matter and energy that relies on descriptions such as Newton’s laws of motion.

population     (in biology) A group of individuals from the same species that lives in the same area.

territorial     (in biology) An adjective for organisms that try to keep others of their species away from an area they control.

2-D      Short for two-dimensional. This term is an adjective for something in a flat world, meaning it has features that can be described in only two dimensions — length and width. 

Citation

Journal:​ R. Gerum et alStructural organisation and dynamics in king penguin coloniesJournal of Physics D: Applied PhysicsVol. 51, No. 16, Published online April 4, 2018. doi: 10.1088/1361-6463/aab46b.