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Number of species: 79

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Bay-breasted Warbler - Setophaga castanea

Bay-breasted Warbler has a partial preformative molt and partial prealternate molts that include some to all greater coverts. The age and sex of many individuals can be determined by plumage, but some are sufficiently intermediate in appearance that age in fall can be reliably confirmed only through skull ossification.

Quick tips

  • Check the primary coverts, which on FCF/FCA (HY/SY) individuals tend to be dull brown, contrasting with darker fresher greater coverts; DCB/DCA (AHY/ASY) birds have a more uniformly dark wing.
  • Consider the tail - on FCF/FCA (HY/SY) birds the rectrices are typically relatively narrow and pointed, while on DCB/DCA (AHY/ASY) birds they tend to be broader and more rounded; note that unlike in some other warblers, the amount of white on outer tail feathers varies little by age or sex.
  • In alternate plumage (spring/summer), examine the forehead and crown - DCA (ASY) males have a dark chestnut crown and black forehead, FCA (SY) males also have a chestnut crown but with a mottled black forehead, DCA (ASY) females have an olive crown with traces of chestnut, and FCA (SY) females have an olive crown lacking chestnut.
  • In formative/basic plumage (fall/winter), focus on the flanks - DCB (AHY) males have moderate to large chestnut patches, FCF (HY) males and DCB (AHY) females usually show a hint of chestnut, and FCF (HY) females lack any chestnut.

Species account prepared by McGill Bird Observatory (2016). 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)
Olive-gray above; paler below with some spotting; buffy wing bars
No images available yet
FCF - (HY: June - December; SY January - April)
Primary coverts brownish, contrasting with dark gray (F) to blackish (M) greater coverts; rectrices sometimes narrow and somewhat pointed; flanks with (M) or without (F) a hint of chestnut streaking
M
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FCA - (SY: February - August)
Primary coverts generally brown, contrasting markedly with dark gray (F) or blackish (M) greater coverts; rectrices sometimes narrow and somewhat pointed; face grayish (F) or blackish (M)
M
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DCB - (AHY: June - December; ASY January - April)
Primary coverts gray, only slightly lighter than the blackish greater coverts; rectrices generally broad and rounded; flanks with a hint of (F) or distinct (M) chestnut patches
F
Thumbnail - MG2-2440-72099-Setophaga_castanea_AOU_7_52-2188.jpg Thumbnail - MG2-2440-72099-Setophaga_castanea_AOU_7_52-2186.jpg Thumbnail - MG2-2440-72099-Setophaga_castanea_AOU_7_52-2187.jpg
DCA - (ASY: February - August)
Primary coverts grayish, somewhat lighter than the blackish (F) to black (M) greater coverts; rectrices generally broad and rounded; face dark gray (F) or black (M)
No images available yet

Individuals in active molt

FPJ - (HY: June - August)
Similar to FCJ; some natal down remaining and/or juvenile flight feathers still growing in
No images available yet
FPF - (HY: June - August)
Similar to FCF; median and greater coverts and sometimes the greater alula being replaced
No images available yet
FPA - (SY: January - May)
Similar to FCA; head and body feathers, lesser and median coverts, and some to all greater coverts being replaced
No images available yet
SPB - (SY: June - August)
Flight feathers being replaced, with retained juvenile primaries, secondaries, and/or primary coverts distinctly pale brownish and very worn
No images available yet
DPB - (AHY: June - August)
Flight feathers being replaced, with retained primaries, secondaries, and/or primary coverts either distinctly adult (generally grayish, less worn) or intermediate
No images available yet
DPA - (ASY: January - May)
Similar to DCA; head and body feathers, lesser and median coverts, and most to all greater coverts 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 - August Undergoing preformative or prebasic molt, but cycle is not reliably distinguishable
M-FCF / UCU (FCF, SCB, DCB) U/AHY June - April In formative or basic plumage (molt completed), but cycle is not reliably distinguishable
M-FPA / UPA (FPA, DPA) AHY January - May Undergoing prealternate molt, but cycle is not reliably distinguishable
M-FCA / UCA (FCA, DCA) AHY February - August In alternate plumage (molt completed), but cycle is not reliably distinguishable

Number of species: 79

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