Small. Length 10 to 12cm, mass 5.4 to 10.5 g. Adult male in breeding plumage has upperparts uniformly yellowish olive green; forehead supercilium, lores and entire underparts lemon yellow, and crown glossy black forming a prominent cap on top of head. Black eye stands out on yellow face. Breeding adult female is similar but duller overall with a crown that is hightly variable - may be entirely olive, black with olive mottling, black with olive tips or uniformly black (Ammon and Gilbert 1999).
For a comprehensive review of the conservation status, habitat use, and ecology of this and other Montana bird species, please see Marks et al. 2016, Birds of Montana.
Western Hemisphere Range
Bozeman area normal migration periods: May 20 to June 5 and August 10 to September 20.
Breeding territories are usually located in riparian habitat or wet meadows with extensive deciduous shrub thickets. Likes edges of beaver ponds, lakes, bogs and overgrown clear-cuts of montane and boreal zones (Ammon and Gilbert 1999).
Bees, flies, mayflies, spiders, beetles and caterpillars. Occasionally eats berries (Ammon and Gilbert 1999).
One brood per season is normal for high-elevation Rocky Mountains. Course nest reflects available vegetation. Clutch size is 2 to 7 eggs with 4 eggs being most common (Ammon and Gilbert 1999). Nest with eggs on June 6. Egg records are probably similar to those in Colorado which is June 1 to July 3.