Blue-headed Vireo - Vireo solitarius

Blue-headed Vireo has a partial preformative molt and absent to partial prealternate molts that may include up to three (first cycle) or two (definitive cycle) tertials, and rarely also one or two greater coverts. By spring, plumage characteristics of some individuals may be sufficiently intermediate that they should be considered M-FCF (AHY) unless multiple characteristics indicate a particular age. Determination of sex is limited to brood patch / cloacal protuberance during the breeding season.

Although this account focuses on Blue-headed Vireo, it is believed to also apply to the closely related Cassin's and Plumbeous Vireos. In areas of overlap or where all species are rare, exercise caution with species identification.

Quick tips

• Examine the primary coverts, which on FCF/FCU (HY/SY) birds tend to be paler and duller than the greater coverts, whereas on DCB/DCU (AHY/ASY) individuals those feather tracts are similarly dark.
• Look at the outer rectrices - on FCF/FCU (HY/SY) birds they are narrow and pointed, while on DCB/DCU (AHY/ASY) birds they are more broad and rounded.
• In fall, check the upper mandible lining - on FCF (HY) birds it is whitish to pale gray, while on DCB (AHY) birds it is dark gray to black.
• Consider the shape and length of p10 relative to the primary coverts - on FCF/FCU (HY/SY) birds it is rounded and somewhat longer than the primary coverts, while on DCB/DCU (AHY/ASY) birds it is more pointed and shorter than them.

Species account prepared by McGill Bird Observatory (2018). Last updated by Marcel Gahbauer (Mar 2022)