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Number of species: 79

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Yellow-bellied Flycatcher - Empidonax flaviventris

Yellow-bellied Flycatcher undergoes a partial preformative molt, mostly prior to fall migration; partial to incomplete prealternate molts and incomplete to complete prebasic molts occur on the wintering grounds. This sequence of molts results in distinct molt limits among the median or greater coverts (fall-winter) or among the primaries and secondaries (spring-summer), and allows for FCF (HY), FCA (SY), and DCA (ASY) birds to be distinguished through fall migration. Sexes are identical in plumage; breeding females have a brood patch, but males have a poorly developed cloacal protuberance and may be difficult to identify with confidence.

Yellow-bellied Flycatcher is similar in appearance to several other Empidonax flycatchers, most notably Acadian, Cordilleran, and Pacific-slope. Note the yellowish and rounded eye-ring and combination of uniform and distinctly green upperparts and yellowish throughout the underparts.

Quick tips

  • Examine the primaries and secondaries for evidence of an eccentric molt, which is absent in FCF (HY) birds, but typically present to some degree in all older age classes.
  • Check the shape and condition of the rectrices. They are narrow and pointed on FCF (HY) birds, vs. broad and rounded for all older age classes, but they appear fresher on FCA (SY) individuals than on DCA (ASY) individuals.
  • Look for a distinct molt limit among the greater coverts in FCF (HY) and DCA (ASY) birds, or between the greater and primary coverts in FCA (SY) birds; DCB (AHY) individuals generally lack such a molt limit, but note that this plumage is generally only seen on the wintering grounds.

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; buffy wing bars
U
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FCF - (HY: July - December; SY January - April)
Primary coverts, primaries, and secondaries relatively uniform in appearance; rectrices fairly narrow and pointed; buff-tipped outer greater coverts contrasting with whitish-tipped inner greater coverts
No images available yet
FCA - (SY: March - October)
Primary coverts and often central block of primaries and secondaries contrastingly pale relative to rest of wing; rectrices fairly broad and rounded and fresh
U
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DCB - (AHY: August - December; ASY January - April)
Primary coverts, primaries, and secondaries relatively uniform in appearance or with some innermost secondaries and outermost primaries contrastingly paler and more worn; rectrices fairly broad and rounded; greater coverts uniform with whitish tips
No images available yet
DCA - (ASY: March - October)
Primary coverts and primaries either uniformly dark with greenish edging, or inner primaries slightly paler and more worn; inner greater coverts contrastingly fresh and dark; rectrices fairly broad and rounded but somewhat worn
U
Thumbnail - MG2-9900-16001-Empidonax_flaviventris_AOU_7_52-3526.jpg Thumbnail - MG2-9900-16001-Empidonax_flaviventris_AOU_7_52-3524.jpg Thumbnail - MG2-9900-16001-Empidonax_flaviventris_AOU_7_52-3525.jpg

Individuals in active molt

FPJ - (HY: June - July)
Similar to FCJ; 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 median coverts, some inner greater coverts, and often some to all tertials being replaced
No images available yet
FPA - (SY: March - May)
Similar to FCA, with rectrices, some to all outer primaries, and some to all inner secondaries being replaced
No images available yet
SPB - (SY: August - October)
Flight feathers being replaced, with retained juvenile primaries, secondaries, and/or primary coverts distinctly brownish and very worn
No images available yet
DPB - (AHY: August - October)
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: March - April)
Similar to DCA, with body feathers, inner greater coverts, and some to all tertials being replaced
No images available yet

Applicable unknown plumage/age classes

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

Number of species: 79

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