Wilson's Warbler - Cardellina pusilla

Wilson's Warbler has a partial preformative molt, and absent to limited prealternate molts that are restricted to head feathers. Sex can generally be determined by plumage, but age can be somewhat trickier, and especially by spring there may be some intermediates that are best considered as M-FCU (AHY).

Quick tips

• Examine the crown - DCB/DCU (AHY/ASY) males have an extensive solid black cap, FCF/FCU (HY/SY) males and DCB/DCU (AHY/ASY) females have a somewhat smaller black cap with greenish flecks (usually glossier on males), and FCF/FCU (HY/SY) females have a mottled yellow/green crown with flecks of black.
• Look at the rectrices - on FCF/FCU (HY/SY) birds they are relatively narrow and pointed, and on DCB/DCU (AHY/ASY) birds they are relatively broad and rounded, though the contrast is not as great as on some other warblers.
• Check for molt limits on the wing, although they can be subtle in this species - on FCF/FCU (HY/SY) birds there tends to be somewhat of a greater contrast between dull/paler primary coverts and the slightly darker and fresher greater coverts; in DCB/DCU (AHY/ASY) birds the wing is more uniform in appearance.

Species account prepared by McGill Bird Observatory (2016). Last updated by Marcel Gahbauer (Mar 2022)