What is the definitive field mark for an adult breeding male Mourning Warbler?

Answer

A complete black patch covering the throat and breast

The adult breeding male is characterized by a striking, extensive black area covering both the throat and breast, contrasting with his olive-green back and yellow underparts. This feature is what gives the bird its evocative name.

What is the definitive field mark for an adult breeding male Mourning Warbler?
birdornithologyidentificationwarbler