Yellow Rumped Plumage Change

Today at the bird feeder I am noticing Yellow-Rumped Warblers beginning to get plumage more resembling breeding pattern.  There are more patches of black along the outer breast, the auriculars are darkening, a yellow crown is present, and overall less of the mousy brown color as black feathers are replacing the brown feathers on the head and back. These are both of the Myrtle sub-species.

Canon EF 100-400mm f/4.5-5.6L IS, ISO-800, 400mm, f/8, 1/500 sec, Flash

Canon EF 100-400mm f/4.5-5.6L IS, ISO-800, 400mm, f/6.3, 1/500 sec, Flash