A larger warbler that pumps its tail up and down almost constantly. Alternate Adults olive-brown above with a rusty-chestnut cap, yellow supercilium, submoustachial stripe, and throat. Two subspecies: western birds are browner above, have yellow throat, mostly whitish underparts with crisp brownish streaking and bright yellow undertail coverts. Eastern is slightly larger than western, entirely yellow from the throat to undertail coverts, and heavier rufous streaking. All ages of both subspecies show a dark line through the eye and an obvious supercilium, which may be either yellowish (eastern) or whitish (western). Basic Adults and hatch-year birds are very similar. Western birds are dingy olive-brown above, pale gray to grayish-brown below, with very weak streaking along the flanks, and conspicuous yellow undertail coverts. Eastern birds are warmer brown above, dingy white on the throat, and mostly dull yellow on the breast and belly with barely noticeable streaking. Undertail coverts are brighter yellow than the rest of the underparts.

Length: 14 (cm) Wingspan: 21 (cm)

Voice:

Call a sharp tick. Song a slightly buzzy, uneven trill, zew-zew-zew... strongest in the middle.

Habitat:

Breeds in boreal forests near bogs, weedy fields, or open forest edges. Winters and migrates through brushy, marshy areas.

Behavior:

Outside of breeding range found in mixed flocks, frequently foraging on the ground. Often detected by distinctive, constant tail bobbing.

Feeding:

Mostly feeds on insects, but will also eat nectar.