Chunky, skulking warbler that favors dense undergrowth. Yellow below and olive above with blue-gray head and chest. Blacker lores set off distinctive white arcs above and below eye. Adult males show darkest head; females and immatures have paler gray head and whitish throat. Found in thickets, clearcuts, open mixed forests, and riparian zones. Breeds primarily in mountainous regions of western North America; winters from Mexico to Costa Rica. Compare with Mourning Warbler, but little range overlap, and note longer tail and white eye-arcs on MacGillivray’s.