Penguins are more than cute, tuxedo-wearing birds. Penguins come in all sizes, from the great, 1.1 meters tall Emperor Penguin to the little, 41 cm Fairy Penguin. The trademark coloration of penguins is called "countershading." With white bellies and dark backs, they blend in with the light sky above and dark water below when swimming. Penguins are flightless birds, with their little wings taking on the role of flippers. Their streamlined bodies and short necks make them quick and agile swimmers and hunters, and their heavy, sleek beaks also aid in swimming and catching small fish. One way that penguins are unique among birds is that they do not have lightweight, pneumatized bones; since they're swimmers they don't need it!

One thing that penguins do need, however, is the ability to stay warm. Penguins have thick feathers that keep water out and warmth in, and they have subcutaneous fat, or fat under the skin. Penguins can also control blood flow to their bare, webbed feet to keep them from freezing.

humboldt swimming
Streamlined for swimming. Credit Su Neko.