25 May 2013

Why are penguins flightless? It’s evolutionary

Chinstrap penguin.
Photo credit: Kyle Elliott and Uli Kunz.
The mystery of the flightless tuxedoed bird has intrigued many of us, scientists included.

“Like many people,” said Professor John Speakman, “I have been fascinated by films of penguins walking across the Antarctic ice, and wondered why on earth they lost the ability to fly.”

Speakman, from the University of Aberdeen, Scotland, and the Chinese Academy of Sciences, Beijing, is part of an international research team that collected data solving the puzzle of why penguins don’t take to the skies.

“The lack of flight in penguins has been an enigma, because it leads to some seemingly poorly adapted behaviour,” he said.

“Emperor penguins, for example, walk up to 60km between their rookeries and the sea – a journey taking several days that could be covered in a few hours if they were able to fly.

“Also, many penguins are targets of predators such as leopard seals, at the points where they enter the ocean. This problem could be easily avoided if penguins could just fly over the top of the predators.”

Photo credit: Kyle Elliott and Uli Kunz.
The answer to this “enigma” came not from studying penguins, but from looking at their northern hemisphere relatives, guillemots. Also known as murres, guillemots are seabirds in the Auk family which closely resemble penguins in their diving and swimming behaviour, but are still able to fly.

The scientists, whose findings were published in Proceedings of the National Academy of Sciences, explored a biomechanical theory – that a wing that is good for flying cannot be as good for diving or swimming. This is because a wing designed for optimal diving performance is unlikely to be efficient for flying.

“Bottom line is that good flippers don’t fly very well,” said Kyle Elliott, a graduate student at the University of Manitoba, Canada, and first author of the paper.

The team studied how much energy guillemots on Coats Island in northern Canada used during flight and when they dived beneath the waves.

They found that guillemots used substantially less energy than most other birds when they were diving, but the energy they needed for flight was the highest ever reported for a flying bird – 31 times greater than the energy they expended when at rest.

The scientists believe these findings explain why penguins can’t fly.

Speakman said, “Our findings for the energy expended when diving and swimming by guillemots fit exactly into the predictions of the biomechanical model.”

“... However applying the biomechanical theory to penguins, their loss of flight may have been due to the tradeoffs in maximizing wing function in water versus wing function in air.

“As penguins evolved, their wings became more and more adapted to swimming and diving in the oceans where they catch their food – making this part of their lives very energy efficient.

“However, at the same time the energy required for flying became greater and greater for the penguin. At some point, it simply became impossible to sustain the very high energy costs of flight, and the birds became flightless. Presumably the efficiency benefits when feeding offset the inefficiency of having to walk everywhere when they were on land.

“Our studies of guillemots ... have now shown that this biomechanical theory is very likely to be correct. Guillemots resemble penguins in their diving and swimming behaviour, but differ in that they are still able to fly. In many respects they are like a modern equivalent to the ancient ancestors of penguins before they lost the ability to fly.”

The paper is a collaboration involving the University of Manitoba, Winnipeg, Canada; University of Missouri, St Louis, USA; Canadian Wildlife Service, National Wildlife Research Centre, Carleton University, Ottawa, Canada; University of Aberdeen, Scotland and Chinese Academy of Sciences, Beijing, People’s Republic of China. 

Penguins may have 'happy feet' but why don't they fly?, 20 May 2013, University of Aberdeen

Proceedings of National Academy of Sciences citation
Elliott, K. H., Ricklefs, R. E, Gaston, A. J., Hatch, S. A., Speakman, J. R., & Davorena, G. K. (2013). High flight costs, but low dive costs, in auks support the biomechanical hypothesis for flightlessness in penguins. Proceedings of the National Academy of Sciences of the United States of America, published ahead of print 20 May 2013, doi:10.1073/pnas.1304838110

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