The ruby-crowned kinglet is a small, greenish, active bird recognizable by its big white eye ring, white wing bars, and tiny bill. In breeding season it is a bird of coniferous and mixed woodlands, but in winter it favors thickets, brushy areas, and woodlands with a thick understory.
The song is improbably loud and musical for so small a bird. Observers who hear one before seeing it often assume it is a much larger species. The song is long and consists of whistles, short clear notes, and a rapid warbling series of mixed notes. The common winter call is a hard djit, often run together in a rapid series when the bird is excited or agitated.
Listen to the ruby-crowned kinglet: