Tuesday, August 09, 2011

Condensed penguins

During my time in Canada, the coldest temperature I recall reading off the digital display on the way back home was -28°C. I couldn't help asking myself why did humans ever settle in such hostile environment (and wtf was I doing there). But if you think Canadians are though (and Germans wimps), hear the story of the Emperor Penguin (Aptenodytes forsteri), that lives in Antarctica.

The Emperor Penguin's adaption to the cold, which can drop down to -50°C during the Antarctic winter, is plainly amazing. Feathers, fat, and their ability to increase the metabolism rate at low temperatures allow the penguins to survive. Equally amazing, but also bizarre, is the Emperor Penguin's breeding behavior.

Penguin colonies up to some thousands have nesting areas inland that are, depending on the annual ice thickness, 50-120 km away from the edge of the pack ice. At the beginning of the Antarctic Winter, some time in March or April, the penguins get out of the water and travel to their nesting areas, mostly walking or sliding on the ice. After mating, the female lays a single egg in late May or early June and passes it on to the male for incubation while she walks back to the shore.

In an environment of ice, snow, and the occasional rock the penguins can't build nests, so they balance the egg on their feet in their brood pouch. And, since there isn't much fish to find on the pack ice, they don't eat. Yes, you read that correctly: They walk a hundred kilometers, the female lays an egg and walks back a hundred kilometers, while the male sits on the egg for another 2 months, during the Antarctic Winter, in the dark, without the female, and all that without eating a thing. By the time the egg hatches, the male has fasted for almost 4 months, lost half of his body weight, and hopes for the female to return because he has nothing to feed the chick. And then he still has to walk back to the shore so he doesn't starve. But hey, my husband assembled the baby cribs!

There's a great documentary, "The March of the Penguins," telling this story:



But the penguins know some physics too!

While a single penguin is able to maintain its core body temperature in the freezing cold, this costs a lot of energy which he can't afford during his Winter fast. So what the Emperor penguins do is they form huddles. The density of the huddles increases with falling air temperature. If the huddle gets very dense, the penguins are in a nearly hexagonal arrangement. In a study from about a decade ago, researchers glued measuring devices to some penguin's lower back. They found that the temperature inside huddles can reach as much as 37.5° (Gilbert et al, arXiv:q-bio/0701051v1 [q-bio.PE]).

The penguins in these huddles do not stand still, but they move in occasional small steps which have recently been subject of another study (Zitterbart et al, PLoS ONE 6(6): e20260). The researchers shot movies of the penguin huddles and tracked the position of the birds. As you will easily notice if you read the paper, David Zitterbart is a condensed matter physicist who compares the huddling penguins to particles with an attractive interaction and the tight huddling to a jamming transition in granular materials. Just that the penguins manage to prevent jamming by coordinated movements. The little steps of the penguins propagate through the huddle like density waves. They measured densities up to 21 birds per square meter.

According to their paper, the penguins' little steps have a three-fold benefit. One is that they help the packing to get denser, much the same way like tapping a bag with ground coffee. The second is that they move the whole huddle, allowing huddles to merge and adjust position and direction. The third one is a turnover of penguins in the huddle, moving those from the outside towards the warmer inside. Though one might argue that what actually is responsible for the turnover is not the little forward steps, but the penguins on the front leaving the huddle and joining it (or another huddle) on the back. But without the forward steps, the turnover would make the huddle move backward.

The below movie from Zitterbart et al's paper (Yes, we live in the age of Harry Potter, where paper has moving pictures!) shows a time lapse of the penguin huddling (actual time about 1h):



I was very confused about the penguin turnover because in all the Emperor Penguin huddles in "The March of the Penguin" and photos I had seen only penguin backs and could not for the hell of it figure out where the penguins are supposed to go if they are all facing towards each other. So I wrote an email to David Zitterbart who kindly explained that there's two different kind of huddles that have been observed. Those that they've described in their paper, which have a forward direction, and circular ones that I had seen images of. He writes that no one really knows how the circular ones work, but they hope to find out with the next experiment.

19 comments:

Plato said...

Interesting physics on the penguins

Reminded me of Happy Feet and penguin designs

Interesting the correlations that can be made?:)

Best,

Eric said...

Notes of mad scientist of ideas for artificial nuclear fusion

1. Magnetic isolation via Tokamac
2. Lasers
3. Penguins

Anonymous Snowboarder said...

Neat stuff and here I just thought the penguins were daft. Bee surely you had lower than -18F? on my side of the border we always get at least a few -25 to -30 nights. Its at the point now I can tell how cold it is by the sound I make walking on the snow!

Uncle Al said...

If you spit into the air and it crackles before it hits the ground, it's cold. If YBCO floats a magnet, it's really cold. If lawyers have their hands in their own pockets, it's cryogenic.

Michigan is so hot that corn pops in the fields. Cows, thinking it is snow, freeze to death. Uncle Al walked a mile uphill in both directions to and from the Moo U NMR room, fighting off mosquitoes with a 5-lb baby sledgehammer. If only there had been penguins.

Bee said...

Hi Snowboarder,

Ontario Winters are comparably mild. If I thought it was really cold, I'd call a friend in Montreal, where it was usually 10 degrees colder still, to cheer me up. I believe it's got something to do with the lake. Anyway, my cold receptors seem to max out at -10C. Below that the only difference I notice is how quickly body parts exposed to the cold get numb. In Germany, the temperatures very rarely drop below -10C. The Winter is typically grey and rainy with occasional rain, around freezing point. Best,

B.

Christine said...

Hi Bee,

I already knew about the role of the male penguins, but not their movements, etc, thanks for the info.

I have recently registered the lowest temperature here in São José dos Campos, southeast Brazil, + 4 C. This is considered very very cold for our standards, and I suppose it cannot get lower, except if this crazy climate changes decide it is time for snow here, for the first time ever.

The lowest temperature I've ever experienced was around 0 C at the Mantiqueira mountains nearby. I think I would die in Canada!!! :<

Best

Christine

Georg said...

What is this behaviour good for? Has there been a time when the antarctic coast was full of dangerous predators?
Or is the coast more windy, thus effectively colder than the region 100 miles from coastline?
Strange
Georg

Phil Warnell said...

Hi Bee,

A truly enlightening piece regarding those wingless birds who always conjures up images for me of them being waiters in tuxedos; having the male of the species as depicted here to being then considered as either extremely patient waiters or dumb waiters;-) More seriously with the strategies they incorporate for keeping warm this has the dumb aspect to be convincingly denied.

In relation to the climate in my neck of the woods I thought you had grown fond of our brisk invigorating winters complimented by the pot holes it produces with some so large they could serve in a pinch as shelters for several Emperor Penguins.

Best,

Phil

Plato said...

It seems Phil that Bee has an obsession about potholes?:)

Plato said...

.....oh and has indeed meet her Waterloo? You called it Phil.:)

Best,

Giotis said...

It doesn't make sense. The female should stay and incubate the egg while the male goes shore to bring food. This is how nature works but I guess political correctness and aggressive feminism ruined this society too.

Plato said...
This comment has been removed by the author.
Bee said...

Hi Giotis,

I'm not a biologist, but my understanding is that the female can't stay because producing the egg costs her too much energy. She has to leave after laying the egg to eat. Best,

B.

Bee said...

Hi Georg,

You mean the long walk back to the nesting place? We've been wondering about this too. Our guess was that this is a relic from some hundredthousand years ago when there wasn't that much ice and the place had some advantage to it. Now it just seems plain stupid. The problem is though that the penguins all breed together, and they need each other for the huddling. So it's not like one penguin can just go next year and breed elsewhere and natural selection will do the rest. They'd have to go all together. So I guess they're stuck there, some sort of local minimum. Best,

B.

Bee said...

Hi Phil,

I'll admit that the Winters in Canada are much prettier than they are in Germany. Also, one gets used to the cold. What I dislike most about the Canadian Winters is that they're so long. Like, in Germany Spring starts February. In Ontario it's more likely May. It feels to me like losing 3 months of the year. Best,

B.

Phil Warnell said...

Hi George & Bee,

Perhaps the Penguins are just better climatologists and meteorologists than we are as to understand the potential impacts of climate change; not all that farfetched as they appear to have a good handle on thermodynamics and the mathematics involved in packing pretty well. The potential in this situation if they were any closer to the open ocean is for their ice shelf to break off and the females losing track of their chicks. Then again maybe they’re just attempting to maintain their privacy; a strategy they will now have to rethink:-)

Best,

Phil

Phil Warnell said...

Hi Bee,

You’re correct of course, as there is really only two recognizable seasons in these parts, with those being winter and construction season; with the latter only affording us enough time to be able to repair the pot holes before winter returns;-)

Best,

Phil

Plato said...

Interesting talk David Deutsch: A new way to explain explanation

When someone announces that the nature-nurture debate has been settled because there is evidence that a given percentage of our political opinions are genetically inherited, but they don't explain how genes cause opinions, they've settled nothing

Best,

Anonymous Snowboarder said...

Bee - I'll take snow over grey cold and rain/sleet! Now that's how you catch a cold.