This rather yellowish green warbler, named for its least conspicuous character, forages lower than many species. It lays 4 to 5 eggs (March–May in west, June in east) in its nest on or near the ground. Polytypic. Length 5".
Adult male: dusky olive green upperparts, grayer on crown and nape. Whitish or yellowish narrow broken eye ring, indistinct dusky eye line. Greenish yellow underparts with indistinct blurry streaks. Undertail coverts always brighter yellow than belly. Adult female: duller and grayer than male. Immature: duller, similar to adult female.
Northern nominate is the dullest, West Coast lutescens is brightest yellow, Rocky Mountains and Great Basin orestera is intermediate, and coastal California sordida (mainly Channel Islands) is darkest green.
Compare with Tennessee warbler. In West, the yellow and Wilson’s warblers are similar to lutescens, but both show plain faces with prominent dark eyes.
Call note: most frequent call a very distinctive, hard stick or tik. Flight call: a high, thin seet. Song: a high-pitched loose trill becoming louder and faster in the middle, weaker and slower at the end; faster in lutescens.
Status and Distribution
Common in West, uncommon in East. Breeding: brushy deciduous thickets and second growth, from boreal forest in East to a great variety of habitats in West. In spring, northern subspecies takes a more westerly route up the Mississippi River Valley, mid-April–late May. Western lutescens moves shorter distances, earlier peaking in late March–early April. In fall, northern subspecies move later than other warblers, peaking in October in much of northern United States. Western subspecies moves earlier, mid-August–early October in Arizona and California. Winter: generally in thickets and shrubby areas from southeast United States and California, through Mexico to Guatemala. Rarely lingers in northern United States. Vagrant: Bahamas (rare), Cuba, Jamaica, Cayman Islands.
Reasonably stable, especially in West, with no significant threats identified.
—From the National Geographic book Complete Birds of North America, 2006