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Number of species: 79

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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)

The molt categories displayed below may be filtered by month.

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Click on any image below to bring up the side-by-side comparison tool.

Individuals not in molt

FCJ - (HY: May - August)
Head and back mostly grayish brown
No images available yet
FCF - (HY: July - December; SY January - March)
Rectrices relatively narrow and pointed; primary coverts contrastingly paler than the greater coverts; p10 rounded and longer than adjacent primary coverts; upper mandible lining whitish to pale gray
U
Thumbnail - MG2-2321-00489-Vireo_solitarius_AOU_7_52-3618.jpg Thumbnail - MG2-2321-00489-Vireo_solitarius_AOU_7_52-3616.jpg Thumbnail - MG2-2321-00489-Vireo_solitarius_AOU_7_52-3617.jpg
FCU - (SY: March - August)
Rectrices relatively narrow and pointed; primary coverts contrastingly paler than the greater coverts; p10 rounded and longer than adjacent primary coverts
U
Thumbnail - MG2-2030-67550-Vireo_solitarius_AOU_7_52-3609.jpg Thumbnail - MG2-2030-67550-Vireo_solitarius_AOU_7_52-3607.jpg Thumbnail - MG2-2030-67550-Vireo_solitarius_AOU_7_52-3608.jpg
DCB - (AHY: July - December; ASY January - March)
Rectrices relatively broad and rounded; primary coverts similar to greater coverts in colour and condition; p10 pointed and shorter than adjacent primary coverts; upper mandible lining dark gray to black
No images available yet
DCU - (ASY: March - August)
Rectrices relatively broad and rounded; primary coverts similar to greater coverts in colour and condition; p10 pointed and shorter than adjacent primary coverts
U
Thumbnail - MG2-2401-97296-Vireo_solitarius_AOU_7_52-3615.jpg Thumbnail - MG2-2401-97296-Vireo_solitarius_AOU_7_52-3613.jpg Thumbnail - MG2-2401-97296-Vireo_solitarius_AOU_7_52-3614.jpg

Individuals in active molt

FPJ - (HY: May - July)
Head and back mostly grayish brown; some natal down remaining and/or juvenile flight feathers still growing in
U
Thumbnail - MG2-1661-08099-Vireo_solitarius_AOU_7_52-3630.jpg Thumbnail - MG2-1661-08099-Vireo_solitarius_AOU_7_52-3628.jpg Thumbnail - MG2-1661-08099-Vireo_solitarius_AOU_7_52-3629.jpg
FPF - (HY: July - September)
Similar to FCF, with most to all greater coverts being replaced
No images available yet
FPA - (SY: March - April)
Similar to FCF, with some body feathers and occasionally outer greater coverts and tertials being replaced
No images available yet
SPB - (SY: July - August)
Flight feathers being replaced, with retained juvenile primaries, secondaries, and/or primary coverts distinctly brownish and very worn
No images available yet
DPB - (AHY: July - August)
Flight feathers being replaced, with retained primaries, secondaries, and/or primary coverts either distinctly adult (dark gray, with moderate wear) or intermediate
U
Thumbnail - MG2-2401-74377-Vireo_solitarius_AOU_7_52-3624.jpg Thumbnail - MG2-2401-74377-Vireo_solitarius_AOU_7_52-3622.jpg Thumbnail - MG2-2401-74377-Vireo_solitarius_AOU_7_52-3623.jpg
DPA - (ASY: March - April)
Similar to DCB, with some body feathers and occasionally outer greater coverts and tertials being replaced
No images available yet

Applicable unknown plumage/age classes

Molt classes Age Months Key traits
M-FPF / UPU (FPF, SPB, DPB) U July - August Undergoing preformative or prebasic molt, but cycle is not reliably distinguishable
M-FCF / UCU (FCF, SCB, DCB) U/AHY July - March In formative or basic plumage (molt completed), but cycle is not reliably distinguishable
M-FPA / UPA (FPA, DPA) AHY March - April Undergoing prealternate molt, but cycle is not reliably distinguishable
M-FCU / UCU (FCU, DCU) AHY March - August In formative, basic, or alternate plumage (molt completed), but cycle and plumage are not reliably distinguishable

Number of species: 79

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