A special post from Alison Boyer whose research encompasses birds and body size evolution.
Penguins are remarkable divers, capable of diving to depths exceeding 200m. The largest penguin species, Emperor penguins (Aptenodytes forsteri), have been recorded diving to 535m and can hold their breath for 15 minutes while actively swimming. Generally, small-bodied vertebrates are limited to shallow diving depths because they are restricted in the amount of oxygen they can store while diving. Penguins partially overcome this limitation with their unique respiratory system. When humans (and other mammals) breathe, our lungs conduct air in and out of the same set of tubes, known as tidal breathing. This means that our lungs are not terribly efficient at extracting oxygen from each breath before exhaling. Penguin lungs, however, have one-way air flow. When a penguin takes a breath, the air moves into a system of air sacs. From there, the air moves through the lungs and into other air sacs until it is exhaled. It it thought that penguins closely regulate the flow of air through the lungs while diving to provide a constant supply of oxygen to the body. In addition, the lung and air sac system is important in regulating buoyancy during dives.
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