Birds in Bulgaria

L 14½-16 cm. Breeds in soggy young deciduous growth along rivers and at swamp edges; can thrive in small stands of dense and shady swamp forest (birch, willow, alder), but not in low shrubland. Summer visitor (mostly mid May-Aug), winters in E Africa. Shy and elusive (except when singing). Nests near ground in dense vegetation.
IDENTIFICATION: A rather large, dark, elongate warbler with broad, rounded tail. Upperparts are uniform dark grey-brown, sometimes with slight olive-green tone. Underparts dirty white with olive-tinged brown-grey flanks. The only salient features are a short and indistinct, off-white supercilium and a contiguous pale eye-ring, diffuse grey mottling (of varying strength; some are poorly marked) on upper breast (sometimes lower throat, too), and olivebrown undertail-coverts with broad whitish tips (produce spotted impression). At close range, outer web of outermost long primary off-white, edge of wing curved, and undertail-coverts cover almost entire length of tail (features common to all Locustella species). Bill rather dark, legs pink. Sexes and ages usually inseparable in the field.
VOICE: Calls not very distinctive, a ‘zrr’ and a throaty ‘tschick’. Song, fortunately, much more characteristic, a remarkable machine-like shuttling which carries on with only short breaks from dusk to morning hours, ‘zre-zrezre- zre-zre-…’ or ‘dze-dze-dze-dze-dze-…’; some variation in tempo (usually rather sluggish) and pitch. The sound can be likened to that of a ‘giant wartbiter’ (i.e. a bush cricket) or a powerful sewing-machine; at close range, a metallic overtone is audible.