‘Happy feet’ but why don’t penguins fly?

An international team of researchers has discovered the secret to why penguins, unlike most other birds, do not take to the skies. The findings emerged following studies of guillemots – seabirds of the Auk family – which closely resemble penguins in their diving and swimming behaviour yet are still able to fly.

The researchers explored a biomechanical theory that a wing 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.

The team of scientists from America, Britain, Canada and China studied how much energy guillemots on Coats Island in northern Canada used during flight and when they dived beneath the waves.

Their findings – published in the Proceedings of the National Academy of Sciences of the United States of America – showed 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, with demands that were 31 times greater than the energy they expended when at rest. The scientists believe their biomechanical findings explain why penguins cannot fly.

Professor John Speakman, a biologist at the University of Aberdeen and at the Chinese Academy of Sciences in Beijing, said the findings for the energy expended when diving and swimming by guillemots were an exact fit with the predictions of the biomechanical model.

“The lack of flight in penguins has been an enigma because it leads to some seemingly poorly adapted behaviour. Emperor penguins, for example, walk up to 60 kilometres 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,” Speakman said.

“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.

“However, applying the biomechanical theory to penguins, their loss of flight may have been due to the tradeoffs in maximising 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, he said.

But at the same time, the energy required for flying became greater and greater for the penguin and, at some point, it became impossible for the bird to sustain the very high energy costs of flight and so it 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, or Murres as they are known in North America, have now shown that this biomechanical theory is very likely to be correct,” Speakman said.

“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.”