L 11½-13 cm. Breeds in northernmost forest belt, in Fenno-Scandia usually in pure upland birch forest and often on sloping ground near a brook, farther E also in coniferous forest with plenty of birch and willow. Summer visitor (in Sweden end Jun-Aug), winters in SE Asia (incl. S Thailand, Burma, Indonesia) and thus has an almost record-long migration route. Active, spends much time in tree crowns, but is not really shy. Nest on ground, no feather lining.
IDENTIFICATION: Just larger than Willow Warbler. Most like Greenish Warbler owing to greenish-grey upperparts, off-white underparts, very distinct and long supercilium, long and broad dark eye-stripe and a short, narrow whitish wing-bar, but distinguished by: bigger size; rather plump body but proportionately not so big head; thicker and more wedge-shaped bill (heavy base, pointed tip), with dark tip to lower mandible (lacking on Greenish); tendency towards olive-grey tinge (at times in form of diffuse spotting) on breast and flanks; dark lores extend to bill-base, but pale supercilium ends short of forehead. Primary projection fairly long. Tertials uniformly greyish-green. Primaries often have brownish edges (just as on Radde’s, by the way). Ear-coverts are usually mottled dark. Exceptionally, wing-bar is worn off on one wing or even on both; occasionally shows hint of a second, shorter wing-bar on median coverts. Legs brownish-pink, sometimes darker brown-grey. Often looks ‘snub-nosed’, with flat forehead and slightly peaked hindcrown.
VOICE: Call a short, sharp, scratchy ‘dzri’ (male bit like Dipper, easily penetrates through noise of rushing brook), quite unlike other Phylloscopus species. Song a fast, rather hard whirring trill at low pitch, ‘sresresresresresresresre…’; recalls Cirl Bunting song; now and then pitch drops (‘vowel change’) or tempo changes halfway through song.