The yellow-billed loon (Gavia adamsii), also known as the white-billed diver, is the largest member of the loon or diver family. Breeding adults have a black head, white underparts and chequered black-and-white mantle. Non-breeding plumage is drabber with the chin and foreneck white. The main distinguishing feature from great northern loon is the longer straw-yellow bill which, because the culmen is straight, appears slightly uptilted.
It breeds in the Arctic and winters mainly at sea along the coasts of the northern Pacific Ocean and northwestern Norway; it also sometimes overwinters on large inland lakes. It occasionally strays well south of its normal wintering range, and has been recorded as a vagrant in more than 22 countries. This species, like all divers, is a specialist fish-eater, catching its prey underwater. Its call is an eerie wailing, lower pitched than the common loon.
Like other loons, it forms long-lasting pairs. The eggs are strongly oval, and are a light purple-brown with darker blotches interspersed.
The yellow-billed loon is a specialist fish eater, yet it also takes crustaceans, molluscs and annelids, especially for its young. It dives in pursuit of prey, which is caught underwater. Probably as a way to avoid spreading parasites, it defecates ashore, in the breeding lake.