In some ways, the auks are the penguins of the Northern Hemisphere, though they are in fact completely unrelated. Both auks and penguins are deep diving seabirds that feed by pursuing fish underwater; however, unlike the penguins, which have lost the power of flight, most auks can fly, though with their fast whirring flight and dumpy bodies it sometimes seems only just. Only one species of auk, the Great Auk, was flightless, and it is now extinct (giving it the dubious honour of being the only species breeding in Britain to become in extinct in historical times).
A small family (only 23 species), auks occur throughout the seas of the Northern Hemisphere. Most species, like the Guillemot, are dark above and white below, which acts as camouflage, though some, such as the Puffin have colourful beaks or, amongst the murrelets, tufts or crests. The legs are set far back on the body making them accomplished swimmers, but rather ungainly on land, and most come ashore only for a short period to breed.