L 10½-12 cm. Breeds in various types of woodland and at various altitudes, in N usually at lower levels in more open forest with some understorey, in S more often on mountain slopes in pine or oak forest. Summer visitor (mostly end Apr-Aug), winters in tropical Africa.
IDENTIFICATION: Not quite size of Willow Warbler. Typical plumage features: yellowish rump which contrasts with duller back; whitish underparts, without obvious yellow or buff on throat, breast or belly; primaries and tail-feathers edged light yellowish-green; tertials dark with contrasting whitish edges; pale-edged secondaries produce pale panel on folded wing; unbroken pale eye-ring; pale lores and light grey ear-coverts, giving pale ‘face’ (but note that in field some show rather dark lores and distinct supercilium); darkish, brown-grey legs. - Variation: Birds from C Europe westward (ssp. bonelli have slight brown cast to the green on crown and mantle/back. In E (orientalis), upperparts slightly more (greenish-)grey, and pale unmoulted greater coverts often form pale wing-bar. See also voice.
VOICE: Usual call a distinctly disyllabic, whistled ‘hü-if’ (bonelli); or a monosyllabic, flat ‘chipp’ (orientalis), almost like House Sparrow fledgling (more muffled on passage, ‘iss[t]’). Both races seem to use the disyllabic ‘hüif’ in agitation. Song a simple repetition of one high note, e.g. ‘svi-svi-svisvi- svi-svi-svi-svi’; voice ‘silvery’ and laughing, a bit like Wood Warbler’s. Some verses run in higher gear, almost like a trill from Blue Tit song, ‘vivivivivivivivi’, commoner in E Europe (orientalis).