Appearance

Adelaide’s Warblers are relatively small warblers (12.5 cm), with yellow underparts and chin, gray upperparts, two white wingbars, a yellow eyebrow stripe, and a gray cheek patch. Their undertail coverts are white, they have a small white or yellow crescent under the dark eye, and they may show a black stripe on the edge of the crown (above the yellow eyebrow).

Although Adelaide’s Warblers are quite distinct, Puerto Rican Vireos (Vireo latimeri) and Bananaquits (Coereba flaveola) sometimes can be confused with Adelaide’s Warblers when viewed through dense vegetation. The Puerto Rican Vireo also has a yellow belly, but it is duller than Adelaide’s Warbler. The vireo also has a brownish-olive back, gray throat, a red or brown iris, and a much stouter bill. Bananaquits also have a yellow belly, but have a dark gray throat, blackish upperparts, yellow rumps, white eyebrow stripes and small, square white patches on the wing. Adelaide’s Warblers also flit through the vegetation more rapidly than these species when foraging. Some of the North American migrant species of warbler, such as Prairie Warbler (Dendroica discolor) and Northern Parula (Parula americana), also could also be confused, as they too have yellow underparts. However, Prairie Warblers have streaked underparts, olive upperparts, yellow wingbars, and more white on the underside of the tail; Northern Parulas may have some reddish or steel blue banding across the breast (depending on the time of year), have more white on the belly, lack eyebrow stripes, and have some greenish-yellow on the nape and back. The Adelaide’s Warbler should be easily identified with a decent view.

Adelaide’s Warblers are very similar in appearance to two other species in the Caribbean, the Saint Lucia Warbler (Dendroica delicata) and the Barbuda Warbler (D. subita). However, these species have disjunct ranges, making identification easy.

Adult male (from Ridgway 1902)

"Above plain slate-gray, the forehead and crown narrowly streaked with black and margined along each side by a narrow black stripe; wings and tail dull black or dusky with slate-gray edgings (paler on remiges, where nearly white terminally); middle and greater wing-coverts broadly tipped with white, forming two distinct bands, of which the posterior one is narrower, the white confined to outer webs, and not extending to the innermost coverts; inner webs of three outermost rectrices extensively white terminally, the white occupying about the terminal half on lateral rectrix; a broad superciliary stripe of yellow, scarcely extending beyond eye, the posterior extremity narrow and whitish; a yellow suborbital spot, separated from the yellow supraloral stripe by a loral streak of black or dusky gray; auricular region and sides of neck plain gray; a spot of black on sides of neck (between gray of sides of neck and yellow of lower throat), with an indistinct whitish space immediately in front of it; malar region, chin, throat, chest and breast lemon-yellow, passing into paler yellow on abdomen and this into white on under tail-coverts, the sides and flanks tinged with olive, but not streaked; under wing-coverts white." The outer three rectrices have the distal third to half of the inner webs white, and the third rectrix (fourth from outside) has a small patch of white at the tip (Curson et al. 1984).

Adult female (from Curson et al. 1984)

Similar to the adult male, but duller and with a narrower black stripe along edge of crown. The outermost rectrix has the distal third to half of the inner web white, the second outermost (the fifth rectrix) has the distal quarter to third white, and the fourth rectrix has no more than the distal quarter white.

First-year male (Curson et al. 1984)

"Very similar to adult female, but edges of remiges, alula, primary coverts and rectrices more brownish- or olive-grey; these retained juvenile feathers also tend to be more worn than the adult’s by spring."  Staicer (1991) reports that bill color differs from adults, but did not describe the difference.

First-year female

Similar to first-year male, but lacking black on head and upperparts often washed olive. The pattern of white in the rectrices is similar to that of an adult female, but the amount of white in the rectrices is slightly less, particularly in the fourth rectrix (Curson et al. 1984).  Staicer (1991) reports that bill color differs from adults, but did not describe the difference.

Juveniles

"Above plain brownish gray, strongly washed with brown on back; no black on forehead or crown; a narrow superciliary streak (scarcely passing beyond eye), suborbital spot, chin, throat, and chest pale primrose yellow or yellowish white, the remaining under parts yellowish white; chest and sides of breast spotted with grayish dusky; wings and tail as in adult, but edgings more brownish or olive-gray and wing-bands narrower and less purely white" (Ridgway 1902).

At six days, chicks were beginning to develop pin feathers for their first-basic plumage; they had black pin feathers, tipped with white, on their spine and head, and a row of yellow pin feathers on the side of their breast, under their wings (Spaulding 1937). However, their wings were bare.  Another observation (A. Wiewel, pers. comm.) found that chicks were completely feathered at eight days.

In the Guánica Dry Forest, southwestern Puerto Rico, Adelaide’s Warblers molt flight feathers in the late summer, starting in July or later, and ending in September. Body feathers are molted at a similar time, from June through October (J. Toms, unpub. data). Wetmore (1916a) mentions them “molting badly” in August, and Staicer (1991) found they initiated molt in July, so this pattern may hold across the island. The timing may vary among individuals, as Wetmore (1916b) found some individuals in worn breeding plumage, while others had feathers in better condition, even though all were breeding in late March (on Vieques). On the other hand, the differences Wetmore noted could merely reflect age differences (i.e. second-year versus after-second-year individuals); the remiges, alula, primary coverts and rectrices are retained in the first pre-basic molt (Curson et al. 1984).

Iris dark brown. Bill blackish, with paler edges (Ridgway 1902). Legs and feet variously described as dark grayish-flesh (Curson et al. 1984), light grayish-brown (in dried skins; Ridgway 1902) or pale yellowish (dried skin; Baird 1872). Bills of six day old chicks were dark gray edged with white, and their legs and feet were gray (Spaulding 1937).

Oniki (1975) measured cloacal temperature in 3 individuals: average temperature was 41.3°C, with a range of 40.9 to 42.0°C.

Length of 3 skins averaged 98.3 mm, with a range of 97-100 mm (Ridgway 1902).