The Yellow-rumped Warbler (Setophaga coronata) is a North American bird species combining four closely related forms: the eastern myrtle warbler (ssp coronata); its western counterpart, Audubon's warbler (ssp group auduboni); the northwest Mexican black-fronted warbler (ssp nigrifrons); and the Guatemalan Goldman's warbler (ssp goldmani).
The genus name Setophaga is from Ancient Greek ses, "moth", and phagos, "eating", and the specific coronata means "crowned".
In summer, adult females have streaked backs of black on blue-green and conspicuous yellow patches on the crown, flank, and rump. This individual is a myrtle warbler, as shown by the white throat.
Since 1973, the American Ornithologists' Union has elected to merge these passerine birds as one species. There is a pending proposal to recognize the Yellow-rumped Warbler as four species rather than as different subspecies.
The Myrtle form was apparently separated from the others by glaciation during the Pleistocene, and the Audubon's form may have originated more recently through hybridization between the myrtle warbler and the
Summer adult male yellow-rumped warblers have slate-blue backs and yellow crowns. As a male myrtle warbler, this individual has a black “mask".
This is a mid-sized New World warbler, though it is one of the largest species in the genus Setophaga (formerly Dendroica) which comprises most of the species in the family. In summers, males of both forms have streaked backs of black on slate blue, white wing patches, a streaked breast, and conspicuous yellow patches on the crown, flank, and rump (the latter giving rise to the species's nickname "butterbutt" among birdwatchers).
Audubon's warbler also sports a yellow throat patch, while the myrtle warbler has a white throat and eye stripe, and a contrasting black cheek patch. Females of both forms are more dull, with brown streaking front and back, but still have noticeable yellow rumps.
Audubon's and the Myrtle are among North America's most abundant neotropical migrants. They are primarily insectivorous. The species is perhaps the most versatile foragers of all warblers. Beyond gleaning from leaves like other New World warblers, they often flit, flycatcher-like, out from their perches in short loops, to catch flying insects. Other places yellow-rumped warblers have been spotted foraging include picking at insects on washed-up seaweed at the beach, skimming insects from the surface of rivers and the ocean, picking them out of spiderwebs, and grabbing them off piles of manure.