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Number of species: 79

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Fox Sparrow - Passerella iliaca

Fox Sparrow has a partial preformative molt and absent to limited prealternate molts. Age-related differences in wing and tail patterns are often subtle; especially by spring, a fair number of intermediates cannot be reliably aged and should be considered M-FCU (AHY). Sex can generally be determined only by brood patch / cloacal protuberance during the breeding season, or by particularly short or long wing chords (e.g., for the eastern race <83 mm = female, >89 mm = male).

The four recognized subspecies differ somewhat in appearance and extent of molt, but the overall patterns are sufficiently consistent for ageing/sexing guidelines to apply to all of them.

Quick tips

  • Look at the tail - outer rectrices are typically narrow and pointed on FCF/FCU (HY/SY) individuals, while broad and more rounded outer rectrices are typical of DCB/DCU (AHY/ASY).
  • Check the outer primary coverts - they are relatively narrow and pointed with minimal pale brown edging on FCF/FCU (HY/SY) birds, compared to relatively broad and rounded with distinct rufous edging on DCB/DCU (AHY/ASY) birds.

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 - September)
Similar to FCF but on average somewhat duller and underparts tending to be more buffy
No images available yet
FCF - (HY: July - December; SY January - April)
Rectrices relatively narrow and pointed; outer primary coverts fairly narrow and pointed, with little or no pale edging
No images available yet
FCU - (SY: March - September)
Rectrices relatively narrow and pointed; outer primary coverts fairly narrow and pointed, with little or no pale edging
U
Thumbnail - MG2-1951-51376-Passerella_iliaca_AOU_7_52-1856.jpg Thumbnail - MG2-1951-51376-Passerella_iliaca_AOU_7_52-1858.jpg Thumbnail - MG2-1951-51376-Passerella_iliaca_AOU_7_52-1857.jpg
DCB - (AHY: July - December; ASY January - April)
Rectrices relatively broad and rounded; outer primary coverts fairly broad and rounded, with distinct rufous edging
U
Thumbnail - MG2-1891-91070-Passerella_iliaca_AOU_7_52-1850.jpg Thumbnail - MG2-1891-91070-Passerella_iliaca_AOU_7_52-1852.jpg Thumbnail - MG2-1891-91070-Passerella_iliaca_AOU_7_52-1851.jpg
DCU - (ASY: March - September)
Rectrices relatively broad and rounded; outer primary coverts fairly broad and rounded, with distinct rufous edging
U
Thumbnail - MG2-2231-00898-Passerella_iliaca_AOU_7_52-1853.jpg Thumbnail - MG2-2231-00898-Passerella_iliaca_AOU_7_52-1855.jpg Thumbnail - MG2-2231-00898-Passerella_iliaca_AOU_7_52-1854.jpg

Individuals in active molt

FPJ - (HY: June - September)
Similar to FCF but on average somewhat duller and underparts tending to be more buffy; some natal down remaining
No images available yet
FPF - (HY: July - September)
Similar to FCF; median and greater coverts and often also tertials and central rectrices being replaced
No images available yet
FPA - (SY: March - April)
Similar to FCF; some head feathers being replaced
No images available yet
SPB - (SY: July - September)
Flight feathers being replaced, with retained juvenile flight feathers distinctly pale brown and very worn
No images available yet
DPB - (AHY: July - September)
Flight feathers being replaced, with retained feathers either distinctly adult (relatively dark, less worn, somewhat broad and rounded) or intermediate
No images available yet
DPA - (ASY: March - April)
Similar to DCB; some head 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 July - September Undergoing preformative or prebasic molt, but cycle is not reliably distinguishable
M-FCF / UCU (FCF, SCB, DCB) U/AHY July - April 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-FCA / UCA (FCA, DCA) AHY March - September In alternate plumage (molt completed), but cycle is not reliably distinguishable

Number of species: 79

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