This is an uncommon to rare warbler in Ontario, although apparently much more common in times past.
They breed where Usnea (lichen) drapes the trees, chiefly near the influence of Lake Superior. They winter from Florida and Mexico south to the West Indies and South America.
The fields marks to look for are the “rainbow” on the chest and the vivid green patch on bluish back. The “rainbow” is a blackish arc, fading to red that merges with the yellow breast.
This is one of many warblers with white wing bars and yellow throat and breast. It also has a white eye ring.
The somewhat similar Nashville Warbler lacks the breast band, and wing bars and has completely yellow underparts: the Parula has a white belly and undertail coverts.
The usual song is a buzzy trill, rising in pitch to an emphatic ending, but some have a song resembling the Cerulean Warbler’s.