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Number of species: 79

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Warbling Vireo - Vireo gilvus

Warbling Vireo has a partial preformative molt and limited prealternate molts that are generally limited to body feathers and difficult to detect. Differences in colour and wear of feathers by age can be subtle, and especially by late spring and summer, many intermediates should be considered M-FCF (AHY) unless evidence for a specific age is particularly distinct. Sex can generally be determined only by brood patch / cloacal protuberance during the breeding season.

Warbling and Philadelphia Vireos can be very similar in appearance; Warbling Vireo can generally be distinguished by having pale gray lores, and with any yellow on the underparts being brightest on the sides and flanks.

Quick tips

  • 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.
  • From summer through early winter, check the upper mandible lining - on FCF/FCU (HY/SY) birds it is pinkish to whitish, while on DCB/DCU (AHY/ASY) birds it is usually gray.
  • Examine the primary coverts, which on FCF/FCU (HY/SY) birds are somewhat paler than the greater coverts, while on DCB/DCU (AHY/ASY) both feather tracts are similarly greenish-gray in appearance.

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 - July)
Brownish-gray upperparts
U
Thumbnail - MH3-2500-65516-Vireo_gilvus_AOU_7_52-3663.jpg Thumbnail - MH3-2500-65516-Vireo_gilvus_AOU_7_52-3661.jpg Thumbnail - MH3-2500-65516-Vireo_gilvus_AOU_7_52-3662.jpg
FCF - (HY: June - 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 pinkish to whitish
U
Thumbnail - MG2-2640-18636-Vireo_gilvus_AOU_7_52-3645.jpg Thumbnail - MG2-2640-18636-Vireo_gilvus_AOU_7_52-3643.jpg Thumbnail - MG2-2640-18636-Vireo_gilvus_AOU_7_52-3644.jpg
FCU - (SY: February - October)
Rectrices relatively narrow and pointed; primary coverts contrastingly paler than the greater coverts; p10 rounded and longer than adjacent primary coverts
U
Thumbnail - MG2-2650-41394-Vireo_gilvus_AOU_7_52-3657.jpg Thumbnail - MG2-2650-41394-Vireo_gilvus_AOU_7_52-3655.jpg Thumbnail - MG2-2650-41394-Vireo_gilvus_AOU_7_52-3656.jpg
DCB - (AHY: June - 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 gray
U
Thumbnail - MG2-2510-81327-Vireo_gilvus_AOU_7_52-3651.jpg Thumbnail - MG2-2510-81327-Vireo_gilvus_AOU_7_52-3649.jpg Thumbnail - MG2-2510-81327-Vireo_gilvus_AOU_7_52-3650.jpg
DCU - (ASY: February - October)
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 - MG2-2600-16020-Vireo_gilvus_AOU_7_52-3660.jpg Thumbnail - MG2-2600-16020-Vireo_gilvus_AOU_7_52-3658.jpg Thumbnail - MG2-2600-16020-Vireo_gilvus_AOU_7_52-3659.jpg

Individuals in active molt

FPJ - (HY: May - July)
Brownish-gray upperparts; some natal down remaining and/or juvenile flight feathers still growing in
No images available yet
FPF - (HY: June - September)
Similar to FCF, with most to all greater coverts being replaced
No images available yet
FPA - (SY: February - April)
Similar to FCF, with some body feathers being replaced
No images available yet
SPB - (SY: June - November)
Flight feathers being replaced, with retained juvenile primaries, secondaries, and/or primary coverts distinctly brownish and very worn
No images available yet
DPB - (AHY: June - November)
Flight feathers being replaced, with retained primaries, secondaries, and/or primary coverts either distinctly adult (grayish, with moderate wear) or intermediate
No images available yet
DPA - (ASY: February - April)
Similar to DCB, with some body feathers being replaced
No images available yet

Applicable unknown plumage/age classes

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

Number of species: 79

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