Originally described as a separate species called Brewster's Warblre, this is a hybrid between Golden-winged Warbler X Blue-winged Warbler. Various hybrid types occur. This F1 type closely resembles the Golden-winged Warbler but has a pale throat and narrow eyeline more like Blue-winged. Although appearing quite different physically, these two species are 99.97 percent alike genetically. These hybrids are becoming increasingly common as the Blue-winged Warbler expands its breeding range northward into the range of Golden-winged. As a consequence, pure Golden-winged Warbler are becoming increasingly rare having suffered one of the steepest declines of any North American songbird in the last half century.
