Sedge warbler

Voice

A hurried, continuously rattling phrase, much rougher than a Reed Warbler's: dry scratches and grating notes alternate abruptly with clear whistles and buzzing trills, without a settled rhythm and without the Reed Warbler's endless repetition — something like cherk-cherk-cherk-trrrrr-tsee-tsee-weedweedweed-krrrr, growing faster and louder until it stops dead. It sings shamelessly in the open from a reed stem or bush top and regularly rises in a short slanting song flight, parachuting back with the tail spread while still singing. Heard from late April to early July, peaking in May, with much night song. Call: a hard tchek and, in alarm, a clattering rattled tcherrr.

Identification

Upperparts warm olive-brown with clear dark streaks on the mantle; the crown is dark and streaked, with no pale central stripe. The most striking feature is the broad, creamy to off-white supercilium, which runs well behind the eye and is bordered above by a dark line. The rump is unstreaked and warm rusty brown and lights up as the bird dives back into cover. Underparts off-white with buff flanks, unstreaked in adults; autumn juveniles are yellower and often show a fine gorget of streaks across the breast. Legs grey-brown, primary projection short, tail rounded.

Confusion species

Aquatic Warbler is the key one and the hard one: it has a broad pale crown stripe between two crisp black bands, a finely streaked rump and two pale braces down the back. Sedge Warbler has streaks only on the mantle, a uniformly dark crown and a plain rusty rump. Savi's Warbler resembles an unstreaked Sedge Warbler in shape, with a plain brown crown, a vague supercilium and a strongly graduated tail with long undertail coverts, and reels rather than scratches. Reed and Marsh Warblers are wholly unstreaked above and have a short, faint supercilium. A juvenile Sedge Warbler on a saltmarsh is occasionally called a Zitting Cisticola; the cisticola is far smaller with a short white-tipped tail.

Habitat

Low, varied, wet vegetation with some upright structure: reed fringes along ditches and canals, damp rank herbage with willow scrub, marshy shores, sedge beds, peat pools, polder reed and wet dune slacks. Unlike Reed Warbler it is not tied to reed standing in water, but it does need an untidy mixture of reed, herbage and low bushes with song posts sticking up above the rest.

Range and movements

Breeds across almost all of Europe east into western Siberia. In the Netherlands it is common in peat marsh, polder land, the Delta and the Wadden area, with tens of thousands of pairs, present from late April to September. Every bird crosses the Sahara to the West African Sahel, where survival depends directly on rainfall. In Spain it breeds sparsely in the north, but in August and September the coastal marshes, rice fields and riverine reedbeds fill with migrants gorging on reed aphids to cross the desert in a single hop.

• Breeding (summer)
• Passage
• Migration direction
• dark = core range, pale = thinly spread

Where and when to look

Mid May, shortly after sunrise, along a reed-fringed ditch in peat marsh or polder: this is when it sings in the open and performs the song flight. Walk slowly and check every bird for the broad pale supercilium and for the warm, plain rump as it drops into cover. If you want Aquatic Warblers, work through every Sedge Warbler in August with the crown and the rump in mind; that discipline is exactly what turns up the rarity.

Conservation status

Not threatened (LC) and broadly stable in Europe, but numbers swing with Sahel rainfall: after dry years the population collapses, after wet ones it recovers within two or three seasons. In the Netherlands it has benefited from wetland creation and unmown banks, following a deep trough in the 1970s and 1980s. Closer to home, drying out, annual mowing of ditch banks and the loss of small reed fringes in farmland are the main pressures.