How did birds like penguins evolve into some of the world’s best swimmers?

“Basically, we tried to understand how wing flapping works in water.”

This is an Inside Science story.

Penguins’ ancient ancestors acquired their ability to swim at the expense of flying, engineers have found.

They mathematically compared the swimming efficiency of penguins to the movements and propulsion of birds like puffins and guillemots, which have not lost their ability to fly but can still swim for short periods while searching for food underwater.

“It’s kind of an engineering practice to think of species as sophisticated engines,” said Peter Dabnichki, professor of mechanical engineering at Australia’s Royal Melbourne Institute of Technology. “Basically, we tried to understand how wing flapping works in water.”

In a recent study published in the Journal of Avian Biology, Dabnichki and his colleagues used mathematical models for how an object creates drag and how it propels itself. Because drag and propulsion work against each other, the combination of numbers can show how well something floats.

All birds are naturally quite buoyant – they need excellent swimming skills to overcome this buoyancy and move down. So it takes a good swimmer to dive deeper. The researchers applied their calculations to the species known as the little penguin. These birds are believed to be the shallowest diving distance penguin species, being able to descend to around 65 metres.

The researchers then performed their calculations on species of alcids, a bird family that includes puffins and guillemots.

The little penguins, they found, sat among some of the alcids and dived deeper than horned puffins, but not as far as Brünnich’s Guillemot—the best diver among the alcids.

“[Little penguins] are surpassed by some of the Alcides in terms of dive speed and efficiency,” said Dabnichki. He added that this isn’t exactly surprising since Alcide increase their depth by bombing from the air. While the researchers didn’t calculate numbers for larger penguins, other published data shows that emperor penguins can outperform Brünnich’s Guillemots. In fact, they can outperform nuclear submarines, Dabnichki said.

Julia Clarke, a professor at the University of Texas at Austin who has worked on penguin evolution but was not involved in the recent study, said Dabnichki’s work shows how efficiently penguins move through water. Penguins’ ability to swim is still underestimated among birds, especially compared to the changes that allowed whales’ ancestors to evolve back to fully aquatic lifestyles, she said.

“The coolest thing is that we’re talking about adapting the flight hub used in air to a medium that’s 800 times denser than air,” Clarke said.

Dabnichki said that long, fragile wings aren’t as efficient when flapping in the water. Penguins’ wings are wider and more fin-like. Most of the well-swimming auks don’t even fully extend their wings while drifting below the surface.

Clarke said fossil evidence tells us penguins lost their ability to fly about 60 million years ago. Alkids are a comparatively younger family of birds, but at least one species of alcid — the great auk found in the North Atlantic — lost its ability to fly, although great auks became extinct in the mid-19th century because they were hunted for down.

It was “remarkable” that different birds independently evolved their wings for swimming, she said. While observing some alcids such as puffins, you can see how the change may have occurred over millennia. “You can see them flying underwater in a group of four or five, and they can fly out of the water,” Clarke said.

The numbers Dabnichki and his colleagues found highlight how these birds made these adjustments in their wing structure that allowed better swimming at the expense of their ability to fly, Clarke said. “These animals never cease to amaze us.”

Inside Science is an editorially independent, nonprofit print, electronic, and video journalism news service owned and operated by the American Institute of Physics.

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