These are probably the best known and most frequently encountered wood warblers. Although variable, all yellow-rumped warblers possess a bright yellow rump, which is shared with only 2 other species. The yellow-rumped’s unique ability to digest the waxes in bayberries allows it to winter farther north than other warblers. Built in June on the fork of a horizontal conifer branch near the trunk at low to moderate height, the yellow-rumped Warbler’s nest contains 3 to 6 eggs. Polytypic (6 ssp.). Length 5.3".
Spring male: crown and back blue-gray streaked with black. Yellow crown patch, distinct rump patch, and patches at sides of breast. White or yellow throat. Black streaks on upper breast and side. White wing bars. White spots in outer tail feathers. Spring female: similar to male, but brownish above with smaller tail spots. Fall adult: similar to spring adult, but generally browner above in both sexes with less black on breast. Immature: similar to spring female; some immature females very dull with indistinct streaking and much reduced yellow on sides of breast.
Six subspecies in 2 groups that were formerly considered full species: “Myrtle” and “Audubon’s.” The “Myrtle” warbler (nominate coronata over most of range and hooveri in Northwest) shows a white throat, black lores and ear coverts, a white line above lores and eye, 2 distinct white wing bars, a broken white eye ring, and large white spots on the outer 3 tail feathers. The “Audubon’s” Warbler (auduboni over most of range, similar memorabilis of the Rockies and Great Basin, nigrifrons of northwestern Mexico, and goldmani of Chiapas and Guatemala) shows a yellow throat, bluish gray sides of the head (inc. ear coverts), 2 broad white wing bars often forming a distinct patch, a broken white eye ring, and white spots on the outer 4 or 5 tail feathers. Some birds breeding in the southwestern mountains are intermediate between auduboni and darker-faced nigrifrons. Subspecific identification is more challenging in winter.
Compare to the Magnolia and Cape May Warblers, which have yellow rumps but also yellow underparts. The palm warbler shows yellow undertail coverts.
Call: the “Myrtle” gives a loud, husky, flat chek; the “Audubon’s” gives a loud and richer chep. Flight call: a high, clear sip. Song: a variable, loosely structured trill, sometimes with 2 parts—the first higher pitched and the second lower and trailing off at the end: chee chee chee chee wee wee wee we. Louder and richer on breeding grounds than in migration. The “Audubon’s” song is similar, but it is simpler and weaker.
Status and Distribution
Common breeder in coniferous woodlands; very common short- to medium-distance migrant to central United States south to Caribbean and central Panama. Breeding: northern boreal and mixed forest, and montane coniferous woodland. Migration: in spring, generally arrives earlier than other warblers, returning to northern breeding areas by late April. In fall, generally migrates later than other warblers, peaking in northern portions of nonbreeding range in late September–mid-October. Winter: a wide variety of habitats from central United States south through Caribbean to western Panama. Vagrant: the “Audubon’s” Warbler is casual in eastern North America. The “Myrtle” Warbler is casual or accidental to Attu I. (Alaska), Baffin Island, Greenland, Iceland (7 recs.), Ireland, Great Britain (22 recs.), Madeira, the European mainland, and eastern Siberia (1 rec.).
Breeding and wintering populations appear stable.
—From the National Geographic book Complete Birds of North America, 2006