The Common Guillemot (Uria troile) is a member of the auk family. It breeds on all rocky coasts of the North Atlantic. The bill is long, straight, and strong, the wings and tail short. In spring, the upper surface of the body is brownish black, the under white, save for the dark throat; in winter, the throat becomes white or mottled. All guillemots lay a single pear-shaped on the ledge of a sea-cliff. They make no nest whatever, and large colonies brood in company.