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Number of species: 74

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Eastern Bluebird - Sialia sialis

Eastern Bluebird has a partial to incomplete preformative molt but no prealternate molt. Sex can be easily determined by plumage, with males always showing more blue than females of the same age class. Age is also often readily apparent from overall appearance, but in case of doubt, closer examination of the wing and/or tail generally allows for quick confirmation.

Quick tips

  • Look at the greater coverts - the presence of a molt limit between fresh blue inner and older brownish outer feathers or between uniformly fresh greater coverts and contrastingly older and browner primary coverts indicates a FCF (HY/SY) bird, whereas DCB (AHY/ASY) individuals have more uniformly fresh greater and primary coverts.
  • Examine the rectrices - if all are relatively narrow or there is a mix of narrow and fresher, broader rectrices this indicates an FCF (HY/SY) individual, but note that uniformly fresh and broad rectrices can occur on both DCB (AHY/ASY) individuals and FCF (HY/SY) birds with a particularly extensive preformative molt.
  • Consider the upperparts - only DCB (AHY/ASY) males are solid bright blue above; FCF (HY/SY) males are mostly blue with a grayish tinge, DCB (AHY/ASY) females are mostly grayish with a bluish tinge, and FCF (HY/SY) females are largely grayish with limited blue.
  • Consider the underparts - FCJ (juvenile) birds are heavily spotted, similar to other thrushes.

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.


Click on any image below to bring up the side-by-side comparison tool.

Individuals not in molt

FCJ - (HY: May - August)
Upperparts brownish-gray, spotted white; underparts pale with dark spotting; primaries, secondaries, and rectrices largely brownish (F) or distinctly bluish (M)
No images available yet
FCF - (HY/SY: July - following October)
Some to all inner greater coverts longer, darker, and bluer than primary coverts and remaining juvenile outer greater coverts (if any) that often have pale tips; rectrices somewhat narrow, mixed with broader feathers, or sometimes all broad
Thumbnail - MG2-2251-52753-Sialia_sialis_AOU_7_52-2940.jpg Thumbnail - MG2-2251-52753-Sialia_sialis_AOU_7_52-2942.jpg Thumbnail - MG2-2251-52753-Sialia_sialis_AOU_7_52-2941.jpg
Thumbnail - MG2-2251-52752-Sialia_sialis_AOU_7_52-2937.jpg Thumbnail - MG2-2251-52752-Sialia_sialis_AOU_7_52-2939.jpg Thumbnail - MG2-2251-52752-Sialia_sialis_AOU_7_52-2938.jpg
DCB - (AHY/ASY: July - following October)
Wing and back uniformly bluish (F) to blue (M); rectrices uniformly broad
Thumbnail - MH3-2261-90727-Sialia_sialis_AOU_7_52-3139.jpg Thumbnail - MH3-2261-90727-Sialia_sialis_AOU_7_52-354.jpg Thumbnail - MH3-2261-90727-Sialia_sialis_AOU_7_52-3140.jpg

Individuals in active molt

FPJ - (HY: May - August)
Similar to FCJ; some natal down remaining and/or juvenile flight feathers still growing in
Thumbnail - MG2-2341-58819-Sialia_sialis_AOU_7_52-2943.jpg Thumbnail - MG2-2341-58819-Sialia_sialis_AOU_7_52-2945.jpg Thumbnail - MG2-2341-58819-Sialia_sialis_AOU_7_52-2944.jpg
FPF - (HY: July - October)
Blue head and back feathers growing in; some to all greater coverts and tertials being replaced, and often some to all rectrices
No images available yet
SPB - (SY: July - October)
Flight feathers being replaced, with retained juvenile primaries, secondaries, and/or primary coverts distinctly pale grayish (F) or bluish (M) and worn
No images available yet
DPB - (AHY: July - October)
Flight feathers being replaced, with retained primaries, secondaries, and/or primary coverts either distinctly adult (relatively dark blue and not overly worn) 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 - 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

Number of species: 74

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