Appearance

The following are based on descriptions of the widespread eastern North American subspecies, D. p. aestiva, in Dwight 1900, Ridgway 1902, Oberholser 1974, Curson et al. 1994, Dunn and Garrett 1997, and Pyle 1997, unless otherwise indicated. Molt in Neotropical, resident forms thought to be generally similar.

Color names that follow Ridgway (1902, 1912) italicized, equated with Munsell color chip notation (hue, chroma/value) following Hamly (1949), and followed by the closest color in Smithe (1975–1981) when available (e.g., pale drab gray, 10YR 8.5/0.5; 119C).

Hatchlings

Natal down is mouse gray (7.5YR 5.0/1.0), visible in all pterylae by 2 d, most noticeable in alar tract (Smith 1943).

Juvenal Plumage

Acquired by complete Prejuvenal (postnatal) molt. No information on timing or sequence of Prejuvenal molt. Sexes similar.

Head and upperparts pale olive gray (7.5Y 8.5/1.0) to olive brown (10YR 3.8/2.0; 28), obscurely streaked with dusky olive on back and rump. Chin, throat and chest pale grayish olive to buffy white; posterior underparts more whitish, unstreaked. Flight feathers dusky to pale clove brown (10YR 2.8/1.5; 21). Outermost primary edged bright lemon yellow, inner webs of rectrices edged lemon yellow (7.5Y 8.0/10.5), but less extensively than in adults. Median and greater wing-coverts broadly tipped with yellowish buff. Dichromatism in Juvenal plumaged Yellow Warblers described from a Wisconsin brood of 2 nestlings: 1 bird olive brown above, brownish ashy below; the other light olive green above, light chrome yellow below (Southern 1961); this difference possibly related to sex of individual (K. A. Hobson, H. L. Gibbs, R. J. G. Dawson and H. E. den Haan unpubl.).

Basic I Plumage

Acquired by a partial but variable Prebasic I (postjuvenal) molt that typically includes all feathers except primaries, primary-coverts, secondaries, and rectrices. Usually includes some to all median-coverts, 3–10 inner greater-coverts, and 1–3 tertials. Occurs Jun–Aug on breeding grounds (Pyle 1997; Fig. 3), often begins before fledging, and may be completed during southward migration (CCR).

This plumage variable, with much overlap between sexes, which are reliably identified only at extremes.

Male. Similar to Definitive Basic female. Forecrown dull to moderately bright yellow (5.7Y 8.34/12.4; 55), often heavily washed greenish. Rest of upperparts yellowish olive green (8.2Y 4.60/6.2; 50), slightly duller than crown. Underparts pale to brightish yellow, sometimes with several distinct chestnut (10R 3.0/5.0; 32) streaks on upper breast, but typically with limited and indistinct or no streaking. Outer greater-coverts, if retained from Juvenal plumage, may show yellowish-buff tips and contrast with duskier, indistinctly tipped, replaced inner greater-coverts. Yellow less extensive on inner web of outer rectrices than in Definitive Basic male, and underparts duller and greener (Dunn and Garrett 1997).

Female. Similar to duller-colored Definitive Basic females. Forecrown and rest of underparts dull, pale greenish yellow (10Y 8.0/7.0) or olive yellow, slightly brighter on rump and uppertail-coverts. Face typically shows indistinct whitish eye-ring. Underparts pale yellow to greenish yellow (10Y 7.8/10.0; 1.8GY 8.2/11.0), without chestnut streaks. Greater-coverts as in Basic I male, outer rectrices averaging less yellow on outer webs than in Basic I male.

Alternate I Plumage

Prealternate I molt partial to incomplete; may involve continuous, limited replacement of body feathers on the wintering grounds Oct–Apr, but most concentrated Dec–Apr (Fig. 3). Includes 3–10 inner greater-coverts, usually 1–3 tertials, and sometimes one or both of the inner-most secondaries, but no rectrices (Pyle 1997).

Male. Similar to Definitive Alternate male, except that crown averages slightly greener and usually lacks any orange or reddish tinge, chestnut streaking on breast and flanks broad but less distinct. Retained Juvenal outer greater-coverts (worn and brownish) contrast with replaced Basic I inner-coverts (fresher, dusky, yellow-edged).

Female. Very similar to Definitive Alternate female, but crown averages slightly more greenish, not contrasting markedly with back coloration; chestnut streaks on underparts narrow and indistinct or lacking. Contrast in greater-coverts between retained outer Juvenal and replaced inner Basic I feathers less apparent than in Alternate I male.

Definitive Basic Plumage

Definitive Prebasic molt complete, Jun–Sep on breeding grounds (Fig. 3). Southern breeding populations undergo earlier molt than northern populations. In Vermont, birds in very early stages of remigial molt (≤3 pri-maries shed) regularly captured from 22 Jun–16 Jul (one exceptionally late female with P1, P2 just shed on 27 Jul); however, some birds calculated to have initiated primary molt as early as 6 Jun (CCR). In James Bay, Ontario, onset of molt spread over 3–4 wk between early Jul and early Aug, with mean date of onset for males (17 Jul) significantly earlier than for females (22 Jul); on average females complete remigial molt in 37 d, males in 43 d (Rimmer 1988). Mean molt duration of Vermont birds similar between sexes, 42–43 d (CCR). Yearlings of both sexes tend to molt earlier than older birds. Timing of molt similar between years for actively molting individuals examined in more than one year (Rimmer 1988, CCR).

James Bay birds regularly overlap molt with care of dependent fledglings, males beginning remigial molt 8.1 d after young fledge (range 1–19), females 12.3 d (range 9–15). Most birds begin southward migration during final stages of remigial molt (Rimmer 1988, CCR). Rapid, intense molt of James Bay birds can involve up to 8 primaries sim-ultaneously and may result in virtual flightlessness of some individuals. Vermont birds rarely molt more than 5 or 6 primaries at one time. Relatively late season migratory departure of James Bay birds may be more closely keyed to aerodynamic than physiological readiness.

Male. Similar to Definitive Alternate male, but yellow of underparts slightly duller and chestnut streaking less distinct; crown, nape, and auriculars slightly to moderately washed with greenish, accentuating yellowish eye-ring and reducing contrast with rest of upperparts.

Female. Very similar to Definitive Alternate female, but averages paler and slightly duller, more washed with greenish; usually with a few (but sometimes no) indistinct, chestnut streaks on upper breast.

Definitive Alternate Plumage

Definitive Prealternate molt partial, includes “continuous, limited replacement” of body feathers (feather tracts not specifically identified; Pyle 1997) and 8–10 inner greater-coverts and 2–3 tertials, but no other rectrices or remiges; occurs Dec–Apr on wintering grounds (Fig. 3).

Male. Crown and forehead bright yellow, sometimes tinged or slightly streaked orange or chestnut, usually contrasting with more greenish-yellow nape and back; rump and uppertail-coverts yellow tinged with olive (5Y 3.8/3.0; 35). Back feathers may contain a few obscure chestnut streaks. Underparts bright yellow, with broad, distinct chestnut streaks across breast and on sides and flanks. Lesser-, median-, and greater-coverts dusky, broadly and uniformly edged with yellow. Remiges brownish olive, tertials broadly edged (outer webs more so) with yellow, outer webs of primaries and secondaries more narrowly edged with yellow. Rectrices dusky olive on outer webs (and on entire R1); r2–R6 extensively pale yellow on inner webs, forming yellow tail spots, R5 and R6 averaging more yellow than in Definitive Alternate female.

Female. Similar to Definitive Alternate male but considerably paler. Crown yellow with greenish wash, contrasting slightly or not at all with greenish-yellow nape and remaining upperparts. Face and underparts pale lemon yellow (8.5Y 8.5/10.0; 55), with narrow and indistinct chestnut streaks on breast, sides and flanks. Yellow margins of median-coverts, lesser wing-coverts, greater-coverts and remiges duller and more greenish, often narrower; rectrices similar but averaging less yellow on inner webs of R5 and R6.

Golden Warbler

Plumages generally similar to Yellow Warbler except that male with well-defined orange to dark chestnut crown (which may be restricted or absent in some individuals of D. p. gundlachi); more yellow and less green. Within West Indies, clinal variation in chestnut crown: pale in Greater Antilles becoming darker and of greater extent southward; ventral chestnut streaking more prominent in w. Caribbean populations; northern populations with duller and greener upperparts (see Systematics: geographic varition, above).

Mangrove Warbler

Plumages generally similar to Yellow Warbler except male usually with entirely chestnut head. Many females with chestnut on crown and cheeks and streaking on underparts. D. p. cien-agae (of Venezuela) intermediate between typical Mangrove and Golden warblers. D. p. aureola (of Galapagos and Cocos Is.) and D. p. peruviana (of Peru) have appearance of Golden Warbler (see Systematics: geographic varition, above).

Bill And Gape

Bill of Definitive Alternate male black, tinged grayish along tomium and lower mandible; Definitive Alternate females and birds in Definitive Basic plumages have duller bill with some yellowish on mandible; bill more extensively pale, especially at base, in Basic I birds of both sexes; juveniles have pinkish-buff bill.

Iris

Dark brown in adults and birds in Basic I plumage; no information on juveniles.

Legs And Feet

Pinkish yellow to grayish flesh in adults, soles of feet yellow. Legs and feet pinkish buff in juveniles.