Marbled Murrelets are unusual among the alcids in that they molt to cryptic-brown plumage during the breeding season. In the non-breeding season, they are gray and black mixed with white above with white bellies. The top of the head is dark gray, and the bill is slender. A white throat, chin, and collar mark the face, and white extends up the sides of the rump. A dark band down the shoulders contrasts with the white collar in flight, and the bird has narrow, pointed wings. Juveniles appear similar to adults in non-breeding plumage but with a brownish-tan coloring.