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Emperor penguins may have a supercharged form of a blood protein that allows them to dive underwater for more than 20 minutes on a single breath, a new study suggests.

The research showed that penguins in Antarctica return from long fishing excursions under the sea ice with the lowest blood oxygen levels ever recorded in wild animals.

With such depleted reserves, experts say, other creatures would black out and suffer tissue damage.

The finding suggests that emperors—the largest of all penguin species—may have a hyped-up version of hemoglobin, the blood protein that carries oxygen from the lungs to the body.

Other species are unable to use all the oxygen in their lungs—even when starved for air—because their hemoglobin cannot efficiently bind with and carry oxygen in low concentrations.

But penguin hemoglobin appears to be extra-sensitive, scooping up the last remaining oxygen in the birds' air sacs and delivering it to vital organs.

"We hypothesize that the emperor can store more oxygen in its blood due to different binding properties of its hemoglobin," said lead study author Paul Ponganis of the Scripps Institution of Oceanography in San Diego, California.

"This would allow it to use its lung oxygen completely and would also provide a greater oxygen content at low oxygen pressures so that there is no tissue damage."

The findings appear in the current issue of the Journal of Experimental Biology.

Penguin Ranch

Emperor penguins can dive down to 1,850 feet (565 meters) while searching for fish, squid, and krill in the open ocean.

The penguins have a variety of adaptations that help them increase their ability to store oxygen and control its consumption rate.