A medium-sized loon, common in western North America and across the Pacific to Japan. Dark overall and relatively short-billed for a loon, with a rounded crown and nape. Breeding plumage striking with gray head, white-checkered back, and thin white lines on sides of neck. Nonbreeding plumage is rather dark gray above with a clearly demarcated white throat and even border between gray and white on the neck. Diagnostic dark “chinstrap” is sometimes obvious but can be difficult to see at a distance, and is often absent on first-year birds. Especially similar to Arctic Loon, which overlaps mainly from Alaska to Japan. Pacific is subtly smaller-billed and usually holds its head horizontally. In breeding plumage, Pacific has a paler nape that shines silvery in the sunlight, and thinner white lines on the neck than Arctic. Breeds on lakes and ponds in the tundra. Winters mainly on nearshore ocean waters, sometimes in sheltered bays. Often in loose groups, especially where food is plentiful; sometimes mixes with other loon species. Rare but regular on inland reservoirs and lakes during migration and winter.