Penguins take to the air
Penguins can’t fly. But they can get airborne.
In fact, taking to the air, for even a brief instant, is actually a vital strategy penguins employ to avoid being eating by predators such as leopard seals or orcas.
Now scientists have worked out the secret technique that penguins use to get airborne. It involves wrapping their bodies in a cloak of air bubbles – and it turns out to be the same technique that engineers use to speed the movement of ships and torpedoes through water.
Another interesting aspect of the discovery is that it was made by scientists examining in minute detail footage shot for the programme Blue Planet, a landmark natural history series filmed by the BBC’s own Natural History Unit.
It sounds implausible that penguins might get airborne. These short, squat birds, which tend to live in the colder parts of the southern hemisphere, are renowned for their waddling walks and flapping flippers – which are famously great for swimming, but useless for flying.
But many species of penguin do take to the air.
Due to their body shape, and poor climbing ability, it is difficult for penguins to haul themselves ashore, especially onto rocky shorelines. And it can be almost impossible for a penguin to haul itself out from the ocean onto sea ice.
So penguins leap ashore: they swim at speed to the surface, burst through and briefly get airborne to clear the rocks or ice shelf, and land on their breast.
Smaller species, such as Adelie penguins, can leap 2-3 metres out of the water, landing unscathed onto broken rock. Bigger species, such as Emperor penguins (the largest of all), reach heights of 20 – 45 cm, but that is enough for them to leap out of holes in the ice and clear the ice’s edge.
But one aspect of this leaping behaviour has long puzzled biologists. As the birds swim toward the surface, they trail a wake of bubbles behind them. No one knew where these bubbles come from, or why there are there.
Five years ago, that began to change when a group of biologists met in a pub in Cork, the Irish Republic, before the start of a scientific symposium.
Professor Roger Hughes from Bangor University in Gwynedd recalled how he’d seen a wildlife film in which penguins trailed bubbles in this way and asked his colleague Professor John Davenport, of University College Cork, if he knew why they did so.
Professor Davenport did not, but set off to find out with his PhD student Marc Shorten.
Together they obtained footage from the BBC of its Blue Planet series, which filmed breaching penguins for its Frozen Seas episode.
(Watch below how Emperor penguins first evade a leopard seal, then when the coast is clear, they trail a wake of bubbles before leaping from the water)
The scientists slowed down this footage, analysing the speeds and angles of emperor penguins exiting the water, developing a basic biomechanical model of what was going on.
During this analysis, the researchers made some interesting discoveries. The bubbles of air being trailed by the penguins weren’t coming out of the birds’ lungs via the beak.
Instead, they were coming from the birds’ feathers.
“We were amazed to find that,” Professor Davenport tells me.
The researchers also realised that these air bubbles form a “coat” around the birds’ bodies as they rocket toward the surface at speeds of 19km an hour.
To investigate further, the three scientists teamed up with Professor Poul Larsen from the Danish Technical University in Lyngby, who brought his expertise in mathematics and fluid mechanics to the research.
The four scientists have now just published the results of their study.
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The “coat of air bubbles” first noticed on the Blue Planet footage is indeed what enables the penguins to get air as they leap onto land.
Penguins have great control over their plumage, Professor Davenport tells me.
They raise their feathers to fill their plumage with air, then dive underwater. As the birds descend, the water pressure increases, decreasing the volume of the trapped air. At a depth of 15-20 metres, for example, the air volume has shrunk by up to 75%.
The birds now depress their feathers, locking them around the new, reduced air volume.
The penguin then swims vertically up as fast as it can, and the air in the plumage expands and pours through the feathers.
“Because the feathers are very complex, the pores through which the air emerges are very small so the bubbles are initially tiny. They coat the outer feather surface.”
Crucially, this coat of small air bubbles acts as a lubricant, drastically reducing drag, enabling the penguins to reach lift-off speeds.
This air insulation effect is known to boat architects and engineers. By placing a layer of air around a ship’s hull, or torpedo, for example, designers can dramatically reduce drag, and speed up the boat or weapon’s passage through the water as a result.
But “this process has never been thought of before as having a biological role,” says Professor Davenport.
The penguins also appear to have overcome one other issue that blights naval architects trying to exploit “air lubrication” underwater.
Although a coat of tiny bubbles dramatically reduces drag, it can also have a major slowing effect if the bubbles reach a ship or torpedo’s propeller. That’s because the propeller starts pushing against air not water.
However, a penguin’s flippers, its means of propulsion equivalent to the propeller, are held outside of the bubble clouds, so they are not affected.
This wonderful insight into how penguins leap out of the water has just been published in the Marine Ecology Progress Series journal.
It brings a whole new meaning to the expression “getting air”.
Comment number 1.
At 02:32 14th Jul 2011, Patrick wrote:That is amazingly cool!! Nature is indescribably wonderful.
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Comment number 2.
At 06:22 14th Jul 2011, Lunty wrote:Really interesting... but why use a metric of km/hour? The birds do not jump for an hour or travel a km. Use meters/sec please!
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Comment number 3.
At 06:36 14th Jul 2011, Ostangle wrote:Fantastic! The reverse belly-flop! We still have so much to learn about our world.
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Comment number 4.
At 08:09 14th Jul 2011, heradatus wrote:The expanded air on rising will displace water and so contribute to their acceleration, by Archimedes principle. (The calculation of whether this contribution is significant is left as an exercise for the reader).
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Comment number 5.
At 08:51 14th Jul 2011, BlackPhi wrote:Lunty (2): most of us use either km/h or mph as our base unit of speed (and rough conversion between the two is easy). A comfortable walk is around 5-6 km/h, a comfortable cycle ride is around 18-20 km/h and a drive in town might be at 40 km/h. That gives me a simple context for a penguin going at 19 km/h: cycling speed. A velocity of over 5 m/s is impressive, but lacks such context.
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Comment number 6.
At 09:32 14th Jul 2011, pad wrote:They must also use that air in there feathers as a buoyancy control as well
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Comment number 7.
At 10:46 14th Jul 2011, Kwing-So wrote:The use of "micro-bubbles" by penguins for drag reduction has been suspected ever since Blue Planet has been broadcasted in BBC nearly ten years ago. This is the first time, however, that a scientific analysis has been carried out to show the feasibility of increasing the jumping-out-of water speed from 2 m/s (cruise) to 5.5 m/s. Unlike ships, where the measured drag reduction by micro-bubbles is about 2% in a full-scale test, penguins may have "special" techniques to keep the bubbles near the body all the time to achieve this astonishingly high drag reduction of 70%.
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Comment number 8.
At 13:44 14th Jul 2011, Monkey Dean wrote:The irony of all this is that the BBC did an April Fool's spoof documentary last year?Two years ago? about penguins flying.
Awesome stuff.
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Comment number 9.
At 14:22 14th Jul 2011, BahamasSpurs wrote:This is brilliant. Penguins always make me laugh, amazing creatures!
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Comment number 10.
At 15:56 14th Jul 2011, Moosab wrote:Unbelievable and fascinating. Nature is full of surprises. As our understanding of creatures around us, big and small grows, so we will learn more about miracles of this beautiful planet of ours.
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Comment number 11.
At 17:51 14th Jul 2011, Catalina wrote:Please someone, post a link to the fantastic David Attenborough film of the flying penguins. Pretty please?
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Comment number 12.
At 19:48 14th Jul 2011, eigertiger wrote:Km per hour is fine for speed and distance for some things. All UK Ordnance Survey maps for 50 yrs or more are lined off in Km squares. 3 4 5 is easy to remember. Using 5 km/hr is a fast walk on good path or pavement ... 3 km/hr up hill such as the Ben Nevis path and 4 km/hr down the Ben's path. Nothing to do with Penguins though
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Comment number 13.
At 20:01 14th Jul 2011, Ivan wrote:Comment 11 by Catalina
If you are in the UK, Blue Planet is currently being repeated. You can find it on the iPlayer here:
https://www.bbc.co.uk/iplayer/episode/b0074mhp/The_Blue_Planet_Introduction/
Otherwise, if you have not already come across it, try the BBC Nature Wildlife Finder on this link:
https://www.bbc.co.uk/nature/wildlife
Enjoy.
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Comment number 14.
At 17:31 15th Jul 2011, mike_s wrote:For the benefit of Myky D, the BBC April Fool video about the flying penguins can be found on YouTube, at https://www.youtube.com/watch?v=9dfWzp7rYR4. It was broadcast I believe on 1st April 2008. There is another YouTube video on how it was made at https://www.youtube.com/watch?v=lzhDsojoqk8. Both were posted there by the BBC (www.youtube.com/user/BBC).
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