The American redstart (Setophaga ruticilla) is a New World warbler. It is unrelated to the Old World redstarts. It derives its name from the male’s red tail, start being an old word for tail.
Although perhaps not as common as in the past, this appears to be one of the most stable and abundant species of New World warbler, its numbers exceeded in total by the common yellowthroat, yellow warbler and yellow-rumped warbler, because of much wider natural breeding ranges in those species and perhaps exceeding those in sheer density within appropriate range. source