An auk is a type of seabird that lives in the cold waters of the northern oceans, particularly around the Arctic and North Atlantic. Auks are built for diving: they have compact bodies, short wings, and webbed feet that help them swim underwater to catch fish. While they're powerful swimmers, their small wings make them clumsy fliers, and some species can barely fly at all.

The most famous auk is the great auk, which went extinct in the 1800s. Standing about three feet tall with a black back and white belly, it looked remarkably like a penguin, though the two birds aren't closely related. Great auks couldn't fly, which made them easy targets for hunters seeking their feathers, meat, and oil. The last known pair was killed in 1844.

Today's auks include puffins, razorbills, and murres. These smaller cousins can still fly, though they look a bit awkward doing it. Watch an auk underwater, though, and you'll see an expert: it uses its wings like flippers, “flying” through the water as it chases fish.