Size: L: 15 cm. Wt: 17-18 g. Males and females are similar.
Adult: upperparts mottled brown, with dark brown striping on light brown back, and broad gray eyebrow; breast and sides buffy, with fine dark streaks; belly whitish, unstreaked; bill stout, conical, with dark upper mandible, and pale brownish-orange lower mandible; legs reddish-brown
Juvenile: upperparts as in adult, but with broad buffy eyebrow; breast and sides as in adult; belly grayish, unstreaked; bill and legs as in adult; distinguished from juvenile Swamp Sparrow (Melospiza georgiana) by slimmer bill and buffier underparts
Nestling: altricial and downy; skin dark buffy red; blackish-gray down on head, back, wings, and thighs; mouth red; gape flanges whitish on hatching, becoming yellow