Auks fly through water better than they walk on land
Auks, the family of murres, guillemots, puffins, auklets and murrelets, look like northern penguins but are cousins of gulls. Every living species can fly, yet their wings are really built for chasing fish underwater, where some dive to 100 metres. Only the extinct great auk was grounded.
The family Alcidae holds 25 living or recently extinct species in 11 genera, all confined to the Northern Hemisphere. Sizes run from the least auklet, about 85 grams and 15 centimetres, to the thick-billed murre at roughly a kilogram. Common names split across the Atlantic: the birds Americans call murres are guillemots in Europe, and Europe's little auk is America's dovekie. The word auk comes via Icelandic and Norwegian from Old Norse, and Linnaeus coined the genus Alca for the razorbill in 1758.
Their black-and-white plumage and upright stance invite penguin comparisons, but the resemblance is a moderate case of convergent evolution. Genetic work places auks within the gull suborder, with skuas as their nearest living relatives, the two lines parting about 30 million years ago. Auk wings are a compromise between the ideal diving paddle and the minimum needed for flight, so they must beat them very fast in the air. Uria guillemots and murrelets are the best underwater swimmers, whereas puffins and auklets are better fliers and walkers.
Depth recorders show Uria guillemots reaching 100 metres, Cepphus guillemots 40 and auklets 30. Murres chase fast schooling fish while auklets sift slower krill, and where they overlap with foot-propelled cormorants, auks feed farther offshore. They spend most of adult life at sea, pair for life, lay a single egg and reuse the same nest site year after year, whether on crowded cliff ledges or in burrows.
Cold water is essential. Small fish swim twice as fast at 15 degrees Celsius as at 5, while the birds gain no speed, so pursuit diving fails in warm seas; the southernmost auks survive off California and Mexico thanks to cold upwellings. Fossils go back about 35 million years, and the Pacific now has 19 or 20 species against the Atlantic's six, a gap blamed on Atlantic extinctions. The great auk vanished around 1852.
Source: Auk
