Penguins can move underwater with the speed of a swallow or swift, but cannot fly even as far as a chicken. How did a bird that in some cases shuffles 40 miles to its breeding grounds on unsuitable flippers end up losing its ability to fly there quickly?
A team of researchers from the UK, US, Canada and China have put forward a theory of how the penguin lost its ability to fly, published in the Proceedings of the National Academy of Sciences today.
Professor John Speakman, Chair of Zoology at the University of Aberdeen, was part of the international team and carried out the number-crunching that showed how, over time, penguins found it more advantageous to have a wing suited to swimming than flying.
He said: “Wings that have to do two jobs, flying and diving, can’t be good at both. As a wing evolves to be better at diving it gets worse at flying, until the energy demands of flight become so great that eventually the penguin gives up flying altogether.”
The albatross is an example of a long, light wing well-adapted for flying, while a short wing with heavy bones like a penguin’s is more suited to swimming. “They are complete opposites,” Prof Speakman said.
As its wing evolved, the penguin would have become a better diver and a worse flyer, until one day the prospect of launching itself into the air with difficulty no longer appealed.
To test the theory the team studied auks, a family of seabirds very similar to penguins, that catch fish below the water’s surface but which still have the ability to fly. Using the doubly-labelled water method, Speakman was able to work out how much CO2the birds produced as they swam, flew, or sat about. From this he could extrapolate how much energy these activities needed.
He explained: “We found auks have exceptional diving abilities, almost as good as a penguin, but their flight costs are enormous – the highest ever measured. This matched the theory exactly.”
In their capacity to fly and dive they were “on the cusp” of becoming like penguins, he said. In fact the Great Auk, a species of auk hunted to extinction in the 19th century, had already lost the ability to fly, in keeping with the theory.
Had there ever been a flying penguin? “The fossil record doesn’t actually contain a flying penguin,” he said. “The first one we have was already flightless, and that was about 60 million years ago.”
So while it seems extremely maladaptive to see emperor penguins penguins wobbling miles across the ice to their rookeries, it stems from a trade-off far back in the evolutionary chain that saw their wings adapt to their increasingly aquatic environment and lose the ability to fly.
“When you see them swimming underwater,” Speakman said, “you truly get a sense of what they gained in return.”
Source: The Conversation, story by Michael Parker