The Bay-headed Tanager is a medium-sized tanager in the genus Tangara. It is one of the most variable of all tanagers. Generally the upperparts are green and the underparts are blue; the chestnut-red head is separated from the green back by a yellow to golden nuchal band. The intensity of color on the nuchal band and the color of the upper and underparts of the body vary among subspecies. Males and females are similar, but females are duller in color.
The Bay-headed Tanager may be confused with the Rufous-winged Tanager (Tangara lavinia) where their ranges overlap in Central America, Colombia, and northwestern Ecuador. However, the head of the Rufous-winged Tanager is not as strikingly red as in the Bay-headed Tanager, and the Rufous-winged has less extensive blue underparts than most subspecies of gyrola. Furthermore, the Rufous-winged Tanager has extensive yellow on the upperparts, and has cinnamon-rufous wings (Isler and Isler 1999). Immature Bay-headed Tanagers can be mistaken for the female Green Honeycreeper (Chlorophanes spiza), but the Bay-headed’s distinctive thick, blunt bill separates it from the honeycreeper (Hilty 2003).
Most of the upperparts of Bay-headed Tanagers are green, with a chestnut red or brick red head. The colors of the rump, underparts and wing coverts are geographically variable (see Geographic Variation). The following description of the male refers to nominate gyrola of the northeastern South America; characters of other subspecies are outlined in Geographic Variation.
Adult male: Head brick red, with a narrow golden nuchal collar. Back and rump grass green. Inner wing coverts golden; outer wing coverts grass green, remiges dusky edged with grass green. Underparts green, center of throat throat and of breast and belly light blue. Tibiotarsal feathers rufous.
Adult female: The adult female Bay-headed Tanager is very similar to the male, but tends to be duller in color. The female of bangsi (Costa Rica and western Panama) differs from the male head having a paler chestnut color on the head, mixed with dusky on the crown; the back is duller green; there is less blue on the rump; the underparts are paler; and there the yellow is less extensive on the nuchal band and the wing coverts (Stiles and Skutch 1989).
Juveniles: Immature Bay-headed Tanagers usually are uniformly green, sometimes showing small amounts of red on their heads making them appear indistinct (ffrench 1991, Isler and Isler 1999, Ridgely and Greenfield 2001). In Costa Rica (bangsi), the juvenile can appear mottled or smudgy, as the body plumage is dusky with green or blue tips (Stiles and Skutch 1989).
Little information. In Trinidad, molt is observed throughout the year, leading to speculation that molt and breeding may overlap (ffrench 1991). Furthermore, molt proceeds slowly, with only a single remige replaced at a time (rather than molting two or three adjacent feathers simultaneously); there also may be an arrested molt (ffrench 1991).
Iris: dark brown (Wetmore et al. 1984).
Bill: Blackish, grayish-horn horn at base of lower mandible (Stiles and Skutch 1989).
Tarsi and toes: grayish-flesh or gray to horn colored (Stiles and Skutch 1989, Restall et al. 2007).
Total length: 13.5 cm (Ridgely and Tudor 2009).
Measurements in Trinidad (Snow and Snow 1971), sample size not given: mass: 20.7 g; wing: 73.0 mm; tail: 47 mm; tarsus: 17 mm; culmen length from anterior end of the nares: 8.0 mm; bill depth at level of the anterior end of the nares: 5.2 mm.
Measurements for male and female Bay-headed Tanagers from Wetmore et al. (1984), presented as range (mean). All measurements are in millimeters. Table includes samples from western Panama and Costa Rica of Tangara gyrola bangsi and Tangara gyrola delecticia.
| ||Wing Length||Tail Length||Tarsus Length||Culmen||Sample (n)|
Mass, both sexes: mean 21 g (range 17.5–26.5 g; n = 168; Isler and Isler 1999).
Mass, Costa Rica (bangsi): mean 25.0 g ± 3.0; n = 10 (Naoki 2003).
Mass, Bolivia (catharinae): mean 20.6 g ± 1.6; n = 21 (Naoki 2003).