Monday, October 20, 2014

Penguins dressed for success

Photo by Lloyd Spencer Davis
Photo by Lloyd Spencer Davis

Penguins might be regarded as cute, comedic characters because of the bumbling manner in which they walk, but these birds have been shaped not by the air or land, but by the sea. ''Even Ferrari can't design a shape as efficient,'' Prof Lloyd Spencer Davis says. Any creature that has to spend a lot of time moving through a dense medium such as water is likely to have been shaped by evolution into a spindle. Such a shape reduces drag.

''A shark, a seal, a penguin - there might be slight differences to their form - but in essence they are all battling the same problem: drag,'' Davis writes in Professor Penguin. ''They can have coefficients of drag that are better than we can design with all our computers ... but as a consequence of reducing the drag, they have these short legs. Natural history documentaries often mock penguins because of the way they move on land, yet you'd never say about (champion sprinter Usain Bolt), 'well, he sleeps in a funny position'.''

Two of the most recognisable characteristics of penguins - the way they walk and the way they dress - are a consequence of their evolution to become diving birds that hunt in open oceans. ''Penguins walk upright because their legs have been much reduced in an effort to reduce drag. In essence, penguins have such short legs that they end up walking upright on what are essentially their anklebones. The waddling gait of penguins is not the best means of moving on land. It is just one of the compromises that penguins have had to accept on land in order to rule beneath the waves.''

Davis points out that penguins' coloration, too, is more dictated by the requirements of life in water than by those of life on the land. ''They are open-ocean predators, feeding on krill, fish and squid. They are also open-ocean prey, being fed on by the likes of seals, and sometimes the odd whale or shark, too, if some of the stories are to be believed. In the ocean there is nowhere to hide, either for sneaking up on prey or for evading predators. Camouflage comes in the form of the two-tone suit worn by most oceanic dwellers: dark on top to blend in with the depths when seen from above, light on the bottom to blend in with the surface when seen from below. It is the dominant fashion of the water-obsessed: barracuda, tuna, great white sharks, killer whales, salt-water crocodiles.''
In short, Davis notes, penguins may look like they are wearing tuxedos but, really, they go to the same tailors as all other open-ocean predators.


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