This small vireo is often heard singing from deep within heavy brush. A short primary projection makes this bird appear long-tailed compared to other vireos. Western populations have slightly longer tails than eastern. The face shows indistinct spectacles, with a broken eye ring. There are two pale wing bars, but the upper one is very faint. Western birds have gray upperparts. Underparts are white with a faint yellowish wash on the sides and flanks. The California population (Least Bell's Vireo) has very little or no yellow. Eastern birds are olive-gray above, grayer on the head. The underparts are white with a strong yellow wash on the sides and flanks.

Length: 12 (cm) Wingspan: 18 (cm)

Voice:

Song consists of paired phrases, the first ending on a higher pitch, the second ending on a lower pitch: tweedle tweedle tweedle dee? tweedle tweedle tweedle dum. Call is a soft nasal chee.

Habitat:

Brushy fields, riparian corridors, chaparral, mesquite, early successional forest with dense understory.

Behavior:

Eastern birds bob their tails. Western birds flick tails upwards and to the side and the tail is usually held angled upward in a wren-like fashion.

Feeding:

Gleans insects and spiders from foliage, usually close to the ground.