Emperor penguins Aptenodytes forsteri go on regular underwater forays to hunt fish. They may remain submerged for 20 minutes or more and dive hundreds of metres deep, all on a single breath of air. They have normal lungs for a bird their size, so how do they do it?

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Biologists from Scripps Institution of Oceanography fitted wild penguins at McMurdo Ice Shelf, Antarctica, with miniature sensors (and depth recorders) to gauge the birds’ vital signs before, during and after dives.

How do penguins dive so deep?

The data revealed some surprises. Even before a penguin hits the water, its heart starts to race and it hyperventilates, which primes its muscles with oxygen. Then it dives in and does something, well, breathtaking: it cuts off the blood supply to its muscles to conserve dissolved oxygen for the rest of its body.

At the same time, the bird pumps its veins with oxygen-rich blood, possibly to plan ahead – during a long dive, its heart rate may fall to as low as six beats per minute. With so little circulation through the lungs and ever-lower air stores, it may pay to load up with the vital gas before getting in too deep, so to speak. In this way, a penguin pushes its body to, but not over, the limit. Ultimately, the bird surfaces, takes a deep breath and swiftly flushes its now-starved muscles with oxygen without delay. In just minutes, it fully recovers from its dive.

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Main image: Emperor penguins © Getty Images

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