An auk is a bird of the family Alcidae in the order Charadriiformes. Extant auks range in size from the least auklet, at 85 g (3 oz) and 15 cm (5.9 in), to the thick-billed murre, at 1 kg (2.2 lb) and 45 cm (18 in). They are good swimmers and divers, but their walking appears clumsy. Modern auks can fly (except for the extinct great auk).