The darkest sparrow found exclusively in wet saltmarshes with tall grass. Shares habitat with Saltmarsh and Nelson's Sparrows but Seaside is plainer and grayer overall. Plumage differs slightly among populations: Gulf Coast birds brighter, southern Florida birds show more distinct streaking below, Atlantic birds dullest. All populations have a contrasting white throat, yellow in front of eye, and a long bill. Perches conspicuously when singing, otherwise secretive, especially in winter. Rougher, buzzier song than Nelson's or Saltmarsh Sparrows: a few harsh introductory notes followed by a raspy sigh.