Colonies of king penguins resemble the molecules in a 2D liquid, attracting and repelling one another like bird-shaped particles. This unusual set up allows colonies to protect its members against predators and ensure individual penguins don’t stray too far from the pack during the breeding season, say researchers at the Woods Hole Oceanographic Institution (WHOI) in Cape Cod, Massachusetts.
"King penguin colonies are also of special interest because only they and emperor penguins do not build nests, and no one has previously examined the effect this has on their colonies," Richard Gerum, a PhD student at the University of Erlangen-Nuernberg and lead author of a paper published in Journal of Physics D, explained in a statement. Rather, pairs of breeding king penguins produce a lone egg, which parents then take turns to protect using their feet.
Colonies can be made up of hundreds of thousands of these breeding pairs, which huddle together in tight-knit groups during a long breeding cycle that can last 14 months and more. Within this time, there is some movement early and late breeders come and go, but the overall structure of the colony remains surprisingly static.
This is because king penguins are territorial beasts (unlike their cousins, emperor penguins) and once a pair has stationed themselves at a particular site, they will guard their spot ferociously against any interlopers and predators using their flippers and beaks. During the entire two-month incubation period, pairs of penguins moved an average distance of just 1 meter (3.3 feet), the researchers found.
The team used high-resolution aerial photographs to monitor the coordinates of breeding pairs of penguins at two colonies (one on Crozet Island and another on Kerguelen Island) over a period of several years. Then, using radial distributions and computer simulations, the researchers were able to compare the structure of the colony to solids, liquids, and gases, finding that penguins maintained "a liquid-type order, where most penguins are surrounded by six other individuals."
"This liquid state is a compromise between density – or how compact the colony is – and flexibility, which allows the colony to adapt to both internal and external changes," said senior author Daniel Zitterbart, a physicist at WHOI and an adjunct scientist at the University of Erlangen-Nuernberg.
"For example, if a pair loses or abandons their egg, it leaves a vacancy in the colony, but we never see vacant spots in our aerial images. Presumably, those are filled by penguins that had occupied a less preferred breeding spot."
King penguins are one of the thousands of animals under threat from climate change. The researchers hope this research will help conservationists monitor the health and resilience of penguin colonies.