In Ontario this is usually a rare warbler, breeding only in the far north.
It tends to be a rather late fall migrant, after most other warblers have gone.
It winters from Central America north to southern United States.
This is “the warbler with no field marks”: no bright colours, no wingbars, no eye ring; only a very indistinct line over the eye, faint greenish stripes on the yellowish breast and yellow undertail coverts.
The orange crown is seldom visible.
The fall immature Blackpoll Warbler is somewhat similar but does have wing bars and white, not yellow, undertail coverts.
This is a common songster on Vancouver Island, where I learned to recognize its trill, something like a Chipping Sparrow’s trill, but descending in pitch and fading out at the end.