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)