The Descent of Penguin
Posted By Erik Seedhouse on 30 January 2006
Penguins are world-class free-divers capable of diving to depths exceeding 50m. African penguins dive regularly to 30m and have a depth record of 130m. Adélie Penguins swim almost all the time between the surface and 50m although their deepest recorded dive is 240m. Larger penguins such as the Emperor have been recorded diving to 535m and can hold their breath for fifteen minutes! This species is not short on endurance either -- a group of researchers observed one Gentoo penguin making 450 dives in 15 hours! Using time-depth locator transponders other investigators have tracked Emperor's swimming up to 65km per day.
Like humans, the main problem the penguin faces is being unable to breathe underwater. Having a relatively small body size compared to seals penguins are more restricted in the amount of oxygen they can store while diving. The underwater pressure compresses the air held in the lungs and air-sacs, and consequently these airways only provide about a third of the oxygen requirements needed for each dive.
One of the compensatory mechanisms employed by penguins to overcome oxygen requirements is found in the unique lung structure. Human lungs conduct air in when we inhale and out when we exhale. This means that mammal lungs have blind ends; air enters, stops, and then comes right back out. Penguin lungs, however, were designed so that air never stops. Before examining how penguins dive so deep and stay down so long it is useful to review the structure of their respiratory system.
Early in growth and development of humans and penguins the respiratory system begins as a diverticulum (part of the digestive tract). Later in development the digestive tract and respiratory tract separate. The respiratory diverticulum then forms two lung buds. At this stage, human and penguin lung development are fairly similar. But not for long! Shortly after this stage penguins develop additional organs called air sacs.
Penguins have to breathe air just like mammals and therefore they have to come above water while swimming. Unlike the human free-diver who breathes in a static position on the surface, the penguin takes in lungfuls of air at speed. While swimming, the penguin will alternate underwater locomotion with intermittent jumps out of the water -- porpoising - about every 30m to 50m. The jump phase lasts about half a second and the penguin uses this time to breathe. Other species also employ porpoising but it usually means they are in danger!
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