Myiothlypis (and the similar Basileuterus) are large, heavy bodied wood warblers with a long, slightly rounded tail and a relatively heavy bill. These species usually have dull plumage, dominated by yellows and greens, and most species have striped crowns or a conspicucuous supercilium. Gray-and-gold Warbler, a species of Myiothlypis, basically is two toned. The upperparts are dark gray, with an olive back and a broad black stripe down each side of the crown; the semiconcealed center of the crown is yellow orange, and there also is a short, whitish supraloral streak. The underparts of Gray-and-gold Warbler are bright yellow. Sexes are similar in this species.
Gray-and-gold Warbler is distinctive within its geographic range, and is unlikely to be confused with any other species. Other species of South American Myiothlypis and Basileuterus are more or less olive above, not slate gray. Gray-and-gold Warbler is superficially similar to Fan-tailed Warbler (Basileuterus lachrymosus) of Central America, but these two species are highly allopatric. Fan-tailed Warbler also is larger, with a longer, more strongly graduated tail that is tipped with white, and has an ochraceous wash on the breast. Canada Warbler (Cardellina canadensis) is smaller, with a shorter tail, yellow "spectacles", black or dusky breast streaking, and white undertail coverts.
The following description is based on Curson et al. (1994), and refers to nominate fraseri; see also Geographic Variation:
Adult: Sexes similar. Sides of crown black, with a central, semiconcealed yellow crown stripe. Lores blackish. Supraloral streak white. Rest of upperparts blue gray, except for the center of the back, which is dull olive. Wings and tail blackish gray, feathers edged with blue gray, these edgings broadest on the greater coverts and tertials. Chin white; remaining underparts yellow, becoming slightly paler on the undertail coverts.
Juvenile: This description is based on a single specimen (of subspecies ochraceicrista), which may have begun a preformative molt). Head gray brown; many crown feathers black tipped, and some central crown feathers orange with olive tips. Upperparts gray brown, with a very obscure olive mantle. Yellow of underparts paler than in the adult, and washed with olive.
Little information. There is a complete prebasic molt, following breeding (Curson et al. 1994); there is no information on the extent of the preformative molt (Curson et al. 1994).
Tarsi and toes: yellow brown
Total length: 14 cm (Ridgely and Greenfield 2001b)
Linear measurements (from Curson et al. 1994):
male (n = 1)
wing length: 66 mm
tail length: 57 mm
bill length (exposed culmen): 12 mm
tarsus length: 21 mm
female (n = 3)
wing length: range 62-65 mm
tail length: range 50-54 mm
bill length (exposed culmen): 11 mm
tarsus length: range 21-22 mm
Mass: male, mean 12 g (n = 12; Wiedenfeld et al. 1985); female, mean 11 g (n = 6; Wiedenfeld et al. 1985)