What consistent structural feature is absent in the Mourning Warbler across all plumages?

Answer

Wingbars

A consistent field mark important across all plumages of the Mourning Warbler is the absence of wingbars. This feature helps distinguish it structurally from several other warbler species.

What consistent structural feature is absent in the Mourning Warbler across all plumages?
birdornithologyidentificationwarbler