Red-eyed Vireo has a partial preformative molt, but no prealternate molts. The prebasic molts are unusual in that usually only some coverts, tertials, and rectrices are replaced prior to migration, with the remainder of flight feathers replaced during winter. 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 either FCF (SY) or DCB (ASY) is particularly distinct. Conversely, because of the suspended prebasic molt, some FCF (SY) and DCB (ASY) individuals can be distinguished as late as during fall migration. Sex can generally be determined only by brood patch / cloacal protuberance during the breeding season.
Species account prepared by McGill Bird Observatory (2018). Last updated by Marcel Gahbauer (Mar 2022)
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FCJ - (HY: May - August) | ||||||||||
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Brownish upperparts and faint wing bars, absent in older classes | ||||||||||
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FCF - (HY/SY: August - August) | ||||||||||
Iris grayish brown until mid-winter, then becoming more reddish; rectrices and primary coverts relatively narrow and pointed; upper mandible lining pinkish-gray to white until mid-winter, then becoming darker; tertials and secondaries appear uniform | ||||||||||
F |
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U |
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DCB - (ASY: February - August) | ||||||||||
Iris reddish; rectrices and primary coverts relatively narrow and pointed; upper mandible lining gray; tertials sometimes contrastingly pale and worn compared to adjacent secondaries | ||||||||||
F |
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U |
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FPJ - (HY: May - July) | |
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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 - October) | |
Similar to FCF, with greater coverts and greater alula being replaced | |
No images available yet | |
SPB - (SY: July - December; TY January - April) | |
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 - December; ASY January - April) | |
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 |
Molt classes | Age | Months | Key traits |
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M-FPF / UPU (FPF, SPB, DPB) | U | July - October | 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 |