Blue-necked Tanager is a medium sized member of the speciose genus Tangara. The back and breast are black, with a light blue "hood" that includes the head, nape, and throat. The wing coverts are extensively coppery yellow. The color of the rump varies geographically; it usually is silvery green or straw yellow but is blue in one subspecies. The belly is light blue. Male and female Blue-headed Tanagers are similar in appearance, but female has paler blue head with black scallops reaching the nape (Restall et al. 2007).
Two related species of Tangara have a color pattern that is similar to that of Blue-necked Tanager, Golden-hooded Tanager (Tangara larvata) and Masked Tanager (Tangara nigrocincta). Golden-hooded Tanager, which occurs only west of the Andes, has a sulphur yellow "hood" surrounding a blue face, has blue (not yellow) wing coverts, and a white (not blue) belly. Masked Tanager, which is Amazonian and primarily occurs at lower elevations than Blue-necked Tanager, has a paler blue hood, pale blue (not yellow) wing coverts, and a white (not blue) belly. The male Scarlet-thighed Dacnis (Dacnis venusta) also is superficially similar to Blue-necked Tanager, but the dacnis is smaller with a more slender bill, has black wing coverts and a black face, the underparts are entirely black, and the iris is red; it also has red tibial feathers.
The following description refers to nominate cyanicollis, and is based on Restall et al. (2007) and Hilty (2011); see also Geographic Variation:
Adult male: Plumage is mostly blue and black. Head, nape and throat blue, with black lores and a narrow ring of black surrounding the eye. Back and scapulars black, shading to turquise blue on the lower back. Rump opalescent yellow; uppertail coverts opalescent yellow, tinged with opalescent greenish. Wing coverts opalescent yellow; remiges black, narrowly edged with greenish blue on the primaries, and with broader edgings to the secondaries and bluish green or golden-green edges to the tertials. Rectrices blackish, edged with yellowish green. Breast black. Belly and flanks deep blue, mixed with black. Undertail coverts black with bluish green scaling.
Adult female: Similar to male, but head paler blue and with some black scalloping on the nape (Restall et al. 2007). Note, however, that all species of Tangara are at least moderately sexually dichromatic when ultraviolet reflectance in wavelengths visible to tanagers (but not to humans) is taken into account (Burns and Shultz 2012).
Juvenile: "Dull, undistinguished and almost without markings, largely dull grey to sooty grey above and paler buffy grey below, head usually slightly paler, shoulders and wing-coverts buff, secondaries edged greenish, tail sooty with faint bluish edges" (Hilty 2011).
Subadult: Has developed the yellow wing coverts and black back of the adult; also has some black mottling on the underparts, and some blue on the head (Restall et al. 2007).
In general, most tanagers only molt once a year (Isler and Isler 1987), and this prebasic molt likely occurs after the breeding season (Isler and Isler 1987, Ryder and Wolfe 2009). However, many species have been found to breed in subadult plumage (Isler and Isler 1987). In many species of Tangara, the preformative molt is partial (Ryder and Wolfe 2009). Species in the genus Tangara generally acquire adult plumage after the postjuvenile molt (Skutch 1954: 261). Although a juvenile and a "subadult" plumage are described for Tangara cyanicollis (see Detailed Description), more specific information on molt and its timing is not available for this species.
Iris: dark brown
Tarsus and toes: black, dark slate gray, dark gray, gray
Bare parts color data from specimens in The Field Museum and from Hilty (2011).
Total length: 12 cm (Hilty 2011), 12.7 cm (Hilty 2003), 13 cm (Hilty and Brown 1986, Isler and Isler 1987, Ridgely and Tudor 2009)
wing length, male, melanogaster: range 65-70 mm
wing length (sex?), hannahiae: range 67-69 mm
wing length, female, melanogaster: range 65-68 mm
tail length (sex?), melanogaster: range 44-48 mm
tail length (sex?), hannahiae: range 46-50 mm
Linear measurements from Hellmayr (1936)
Mass, both sexes: mean 17 g (range 14-18.8 g, n = 19; Isler and Isler 1987)