Based on recordings and observations from the Yucatan Peninsula, I present the first formal description of the song characteristics and singing behavior of the Mangrove Warbler. Male Mangrove Warblers sing multiple song types with immediate variety, and song types are shared between neighbors. Responses from a playback experiment suggested that Mangrove Warbler song functions in an intrasexual territory defense context. I compared the fine structural characteristics of songs from one subspecies of Mangrove Warbler (Dendroica petechia bryanti) to that of a widely studied Northern Yellow Warbler subspecies (D. p. aestiva). Songs from these two subspecies are significantly different in length frequency and syllabic characteristics, and principal components analysis separates their songs entirely. These results, when taken together with geographical and morphological evidence, suggest a great separation between Mangrove Warblers and Northern Yellow Warblers.