Similar Species

• Very similar to Common Murre, which has a longer and thinner bill, lacks the white line on the gape, is browner on the back, has flanks streaked with gray, and in winter, has a white face with thin black line extending behind the eyes. In breeding plumage the white of the breast meets the dark throat in a straight line or shallow inverted "U" in Common Murre, but in a sharp inverted "V" in Thick-billed.
• Razorbill very similar from a distance, but is more robust, and has a deeper and blunter bill, and often holds it longer tail cocked up into the air.