King penguin colonies move and organise themselves in a way that is "astoundingly" similar to how liquids behave, according to research published today.
The penguin probe, led by Richard Gerum of the University of Erlangen-Nuernberg in Germany, looked at how king penguin colonies organise themselves at the start of breeding season.
When the time comes to procreate, the normally laid-back birds turn into territorial, pecking beasts who will – like the towel-brandishing holidayer – maintain their position for weeks, even in the face of predators.
The research is the first to investigate the structural order – the behaviour that allows for communication and navigation, as well as protecting against predators – of king penguins.
The birds make their home on subantarctic islands and the Falklands, and are one of two species to incubate their eggs on their feet; the others being Emperors, which huddle together to survive the icy chill of the southernmost tip of the globe.
King penguins don't have this cold to fight so can be much more territorial, meaning that movement within a colony at the start of the breeding season, when some penguins are already incubating eggs and others still seek a mate, is difficult (and dangerous).
As birds join the breeding frenzy, they have to pick a path with the fewest aggressive encounters possible, and then settle on a position. The best spots are taken first and gradually movement drops as the colony runs out of space.
To investigate this process, the researchers used aerial imaging to record the positions of several thousand individuals and breeding pairs, and analysed them with the radial distribution function, which is used to describe the average atomic structure of molecular systems like solids, liquids or gases.
They ran a series of computational models to test their results, and concluded that the movement within colonies was strikingly similar to that of 2D liquid particles with a type of mathematical potential called Lennard-Jones.
This is where molecules have both attractive and repulsive forces. In the case of the penguins, this is territorial pecking radius (repulsive), and space constraints and the need to protect against predators (attractive).
"This is the first work that describes this structure in more detail than just field observations, which aren't as quantitative in regards to the colony structure," Gerum told The Register. "It astounded me how well this energy fitted."
As well as giving a better understanding of how colonies form, the work could be used to assess colony health, which is especially important in the context of climate change.
"It is possible that king penguins will have to move further south," he said. "When we know how the colonies settle, what's important for a breeding spot, we can perhaps predict what are the important factors for them to find new places to breed."
The paper, published in the Journal of Physics D: Applied Physics, reveals that breeding king penguins – either in pairs or as individuals incubating eggs – will end up in the core of the colony. Non-breeders and last year's chicks get forced out to the edges.
Most solitary penguins in the core will be surrounded by six others, with a nearest neighbour separation of 0.67m.
Penguins that are closer than 0.45m are classed as a pair, and – as the saying goes – birds of a feather flock together so penguin duos will tend to cluster with other pairs, even if there's space elsewhere when they choose their spot.
When it comes to the positioning of the breeding birds, the paper describes the liquid state of the colony as a compromise.
A gas-like state of complete free movement wouldn't be possible because there are too many penguins in too small a space; while a solid state would make it "virtually impossible to mend" vacancies – like when a penguin leaves prime real estate – and other local disturbances.
However, the paper also demonstrated the degree to which breeding penguins are rooted to their spot. They "do not move even in the event of substantial external disturbances" like predators – and even then, any movement is localised and tends not to propagate beyond a distance of "one pecking radius", the paper said.
"We saw some scenarios when [an] elephant seal comes near to the colony and the penguins don't want to move," Gerum said. "They'll even start to be aggressive to the seal, to try and scare it."
But the difference between these penguins and those that nest – like rockhoppers – is that kings can move and gaps can be infilled. Nesting birds are stuck so their structural order is less defined.
Gerum said that the next step of the work would be to unpick the way colonies stop moving, which is known as a phase transition. Because penguins remain static – their spots will move less than 1.3m over a period of weeks to months – it is likely that there are a number of ways movement is quenched, the paper said.
It offers two possible explanations: a jamming transition, where particle density increases to the point where particles can't move, or a glass transition, where a drop in temperature leads to a loss of energy, and thus a loss of movement in particles.
For penguins, a jamming transition would be the change from a space where the birds move freely to one where breeding has begun and they start to defend their turf. This means you can't fit the same number of penguins in the same space, effectively increasing the density and causing them to stop moving.
But penguins also choose where to settle down, so they stop their movements and are then locked in by neighbouring penguins guarding their own zones, which would be a glass transition.
"At the moment, we are lacking the data to further investigate these differences," said Gerum.
The team hopes to collect data at more regular intervals, such as every few hours, to examine the process on a more granular level. ®
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