A fairly drab vireo of dense, scrubby vegetation, often near water. Two populations: Eastern birds are brighter, with yellow flanks and olive-green back. Note vague spectacled pattern around eye and one bright white wingbar (sometimes with a fainter upper wingbar). Western birds vary from dull olive above to entirely plain gray, usually with one bright wingbar. Look for long tail, often cocked and flipped around. Very active, flitting around nervously in low bushes and thickets. Listen for fast, scratchy song and harsh scold notes. Compare with the brighter and more contrasty White-eyed Vireo, especially in the East, and with the larger and plainer Gray Vireo in the West.