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Number of species: 71

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Philadelphia Vireo - Vireo philadelphicus

Philadelphia Vireo has a partial preformative molt, but is believed to have no prealternate molts. Age can generally be determined by plumage, although by spring some individuals may appear 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.

Philadelphia and Warbling Vireos can be very similar in appearance; Philadelphia Vireo can generally be distinguished by having contrastingly dark gray lores, and with yellow across the underparts, brightest on the centre of the breast.

Quick tips

  • Look at the outer rectrices - on FCF (HY/SY) birds they are narrow and pointed, while on DCB (AHY/ASY) birds they are more broad and rounded.
  • From summer through early winter, check the upper mandible lining - on FCF (HY/SY) birds it is pinkish to whitish, while on DCB (AHY/ASY) birds it is usually gray.
  • Examine the primary coverts, which on FCF (HY/SY) birds are somewhat paler than the greater coverts, while on DCB (AHY/ASY) both feather tracts are similarly greenish-gray in appearance.
  • Check for p10, which is 2-5 mm shorter than the primary coverts on FCF (HY/SY) birds, and even shorter or entirely absent on DCB (AHY/ASY) birds.

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: June - August)
Brownish upperparts and faint wing bars, absent in older classes
No images available yet
FCF - (HY/SY: July - following August)
Rectrices relatively narrow and pointed; primary coverts contrastingly paler than the greater coverts; p10 slightly up to 5 mm shorter than adjacent primary coverts; upper mandible lining pinkish to whitish
U
Thumbnail - MG2-2500-65707-Vireo_philadelphicus_AOU_7_52-3633.jpg Thumbnail - MG2-2500-65707-Vireo_philadelphicus_AOU_7_52-3631.jpg Thumbnail - MG2-2500-65707-Vireo_philadelphicus_AOU_7_52-3632.jpg
DCB - (AHY/ASY: July - following August)
Rectrices relatively broad and rounded; primary coverts similar to greater coverts in colour and condition; p10 absent or >5 mm shorter than adjacent primary coverts; upper mandible lining gray
U
Thumbnail - MG2-2500-65821-Vireo_philadelphicus_AOU_7_52-3636.jpg Thumbnail - MG2-2500-65821-Vireo_philadelphicus_AOU_7_52-3634.jpg Thumbnail - MG2-2500-65821-Vireo_philadelphicus_AOU_7_52-3635.jpg

Thumbnail - MG2-2500-65310-Vireo_philadelphicus_AOU_7_52-3642.jpg Thumbnail - MG2-2500-65310-Vireo_philadelphicus_AOU_7_52-3640.jpg Thumbnail - MG2-2500-65310-Vireo_philadelphicus_AOU_7_52-3641.jpg

Individuals in active molt

FPJ - (HY: June - August)
Brownish upperparts and faint wing bars; some natal down remaining and/or juvenile flight feathers still growing in
No images available yet
FPF - (HY: July - September)
Similar to FCF, with most to all greater coverts being replaced
No images available yet
SPB - (SY: July - September)
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 - September)
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

Applicable unknown plumage/age classes

Molt classes Age Months Key traits
M-FPF / UPU (FPF, SPB, DPB) U July - September Undergoing preformative or prebasic molt, but cycle is not reliably distinguishable
M-FCF / UCU (FCF, SCB, DCB) U/AHY January - December In formative or basic plumage (molt completed), but cycle is not reliably distinguishable