Pied-billed Grebe has thick, horn-colored bill and brown plumage. Red-necked Grebe is much larger, has a longer bill that is yellow at the base and much less contrasty plumage. Eared Grebe is quite similar but always has a peak or topknot at the center of the crown and a thinner bill that is beveled upwards at the tip. In basic plumage it has a darker face with a contrasting white chin, in alternate plumage it is easily distinguished by the golden ray of feathers radiating from behind the eye, and the black neck. Birds in transition between basic and alternate plumage are best disinguished by structural features, as the plumage can be quite variable.
Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.