L 13½-15 cm. Breeds in extensive, tall reedbeds, less often in bulrushes or rushes or other dense waterside vegetation. Summer visitor (mid Apr-Aug/Sep), winters S of Sahara; very rare breeder in Britain & Ireland, only handful of localities. Moves about discreetly in cover, but not really shy. Nests low down in dense vegetation.
IDENTIFICATION: Bearing in mind habitat (dense, tall reeds) and its uniform brown and off-white plumage, can be confused with Reed Warbler; like that species, it is red-brown above and has short, indistinct, pale supercilium. Differs in: long pale reddish-brown undertail-coverts with diffusely paler tips (usually look almost uniformly coloured in field, but some have pale tips distinct enough to create similarity to River Warbler; cf. latter); curved wing-edge (wing straighter on Acrocephalus); with whitish outer web to outermost long primary; more uniform and slightly darker reddish-brown upperparts (lacks Reed’s usually contrasting warmer red-brown rump); brown-grey wash on breast and tinge of reddish brown-grey on flanks (lacks Reed’s buffy-yellow tones); broader tail with fine dark bars on upperside (requires good light and close view). Legs brownish grey-pink. - Variation: E populations (especially from Caspian Sea eastwards, ssp. fusca) have olive-grey cast above and are generally less red-brown, often have slightly stronger greyish tinge to breast and usually have more distinct pale tips to undertail-coverts, thus in several respects are closer to River Warbler.
VOICE: Call a sharp, metallic ‘pvitt!’. Song most like Grasshopper Warbler’s, i.e. consists of an endless reeling, insect-like sound, given mainly at night. Differs, however (apart from fact that singer perches out in tall, dense reeds!), in higher frequency, lower pitch and in the noise, ‘surrrrrrrrrr…’, sounding more of a hard and noteless buzzing than a high whirr. A possible confusion risk at distance and at night in S and C Europe is the mole-cricket. Song verses begin with an accelerating series of clicks which turn into the reel, ‘pt… pt pt-ptptptsurrrrrrr…’.