Study

Coordinated Movements Prevent Jamming in an Emperor Penguin Huddle

Zitterbart, Daniel P.; Wienecke, Barbara; Butler, James P.; Fabry, Ben

PLoS ONE, 2011

Peer-reviewedfield observationwild

What they did

Emperor penguin huddles were filmed by time-lapse through the Antarctic winter and the movement of individual birds tracked, so that the internal dynamics of a structure normally described only from the outside could be measured.

Studied in: Aptenodytes forsteri
Sample size: time-lapse imaging of huddles in an Antarctic colony

What they found

Huddles are not static. Small movements by individual birds propagate through the huddle as travelling waves, roughly every thirty to sixty seconds, and these waves periodically reorganise the packing. Birds progress from the windward edge through the interior and out again, so position is continually exchanged.

What it means

The authors' reading, and ours. Where they differ, that difference is the point.

How the authors put it

Wave-like coordinated movement keeps the huddle densely packed without jamming and redistributes birds between the cold periphery and the warm interior.

How NatureHQ reads it

The interesting result is that no bird is doing anything social in the sense people assume. There is no queue and no turn-taking rule; each bird makes a small movement when pressure allows, and the aggregate is a travelling wave that happens to circulate everyone through the warm middle. Fairness emerges from packing physics. That is a better story than altruistic penguins, and it is the kind of finding that only shows up when someone films the inside of a thing everyone had already explained.

Limitations

Observational; the mechanism is inferred from movement statistics rather than manipulated.
A single colony, and huddling behaviour varies with weather and colony size.
Individual birds cannot be identified across the whole record, so complete circulation paths are inferred.