How do emperor penguins survive underwater long after their oxygen should be depleted?

Emperor penguins are the undisputed champions of diving in the world of birds. They can travel more than 500 meters below the surface, and stay submerged for more than 20 minutes, even though by all accounts their oxygen should run out in just a fraction of that. So how do they pull off this incredibly cool trick?

As they jump in the water and hold their breath, lactate starts to build up in their muscles until they reach what's called the 'aerobic dive limit', at which point they shift their body over to anaerobic metabolism - a system that works without oxygen. They slow their heartbeat down and completely shut down all non-essential organs. It's almost as if they go into suspended animation, except that they are still animated.

The question is, how do the penguins trigger this transformation? To find out, researchers implanted oxygen monitors in the muscles in a number of the emperor penguins, tracking how deep they went and what happened to the oxygen in the birds' bodies.

They already knew that penguins had three stores of oxygen to draw from when they dive, located in the blood, lungs, and the myoglobin of their muscles. When the birds surfaced, the researchers found two distinct patterns in the ways the levels of oxygen were linked to the dives: sometimes the levels would deplete from the muscles at a steady pace until they hit the anaerobic state. This suggests that when oxygen in the muscles runs out, the anaerobic state kicks in. But they also saw oxygen levels decrease, then plateau, before finally falling far enough to trigger the anaerobic state. This made them think that the penguins were doing the animal version of rerouting power from the shields to the warp core.

Just published in the Journal of Experimental Biology, the scientist's paper reveals that the penguins are capable of isolating their muscles from the rest of their circulatory system. They can deplete the oxygen from their muscles separately from their lungs and blood — which allows them to hit that anaerobic state while keeping some reserves behind in other parts of their bodies. Or, they can prevent the anaerobic state from kicking in, because they are able to reroute the oxygen from the other two systems into the muscles, keeping everything nice and oxygenated.

Using these two methods, the penguins make sure that they enter the anaerobic state only when it's needed most.