Bird’s ID – Yellow-rumped Warbler
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).
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 total length, the species can range from 12 to 15 cm (4.7 to 5.9 in) long, with a wingspan of 19 to 24 cm (7.5 to 9.4 in). Body mass can vary from 9.9 to 17.7 g (0.35 to 0.62 oz), though averages between 11 and 14 g (0.39 and 0.49 oz). Among standard measurements, the wing chord is 6.3 to 8.4 cm (2.5 to 3.3 in), the tail is 5 to 6.6 cm (2.0 to 2.6 in), the bill is 0.8 to 1.1 cm (0.31 to 0.43 in) and the tarsus is 1.8 to 2.2 cm (0.71 to 0.87 in). 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. Goldman’s warbler, of Guatemala, resembles Audubon’s but has a white lower border to the yellow throat and otherwise darker plumage; males replace the slate blue of Audubon’s with black.
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. Common foods include caterpillars and other larvae, leaf beetles, bark beetles, weevils, ants, scale insects, aphids, grasshoppers, caddisflies, craneflies, and gnats, as well as spiders. They also eat spruce budworm, a serious forest pest, during outbreaks.