The sexes are similar in appearance, though females are usually smaller. Adult loons have hard, compact plumage, except that the feathers on the head and neck are soft and velvety. Their bodies are checkered with striking black and white patterns, except in the red-throated loon. Arctic, Pacific, and red-throated loons have lighter colored heads and lack a necklace. The belly and wing linings are white year-round.
All loons have grayish plumage in winter, when immatures tend to resemble adults.
Loons most resemble grebes but are larger and have thicker necks and longer bills. Action Divers Extraordinaire Few birds are more aquatic than loons. Legs set far back on the body force ducks to walk with a distinctive waddle. Loons' legs are set even further back, rendering the birds nearly helpless on land. But loons are among the most talented of diving birds, reaching depths up to 240 feet below the surface, though they seldom stay underwater for more than a minute.