Blyth's Reed Warbler | Acrocephalus dumetorum

Voice

Slow, deliberate and utterly distinctive. The bird sings short motifs — a clear whistle, a nasal tchek-tchek, an imitation of Swallow, Oriole, sparrow, or of a species picked up in the winter quarters on the Indian subcontinent — and repeats each one two to four times before moving on, always with a brief pause between. Unlike in Marsh Warbler, the repetitions of Blyth's are easy to count; that regular, slow rhythm is a feature of the species. It sings mostly at night and at first light, from late May into July, usually half hidden at mid height in a bush. Call: a hard dry tchek and a short rattled tchrrr.

Identification

Cool greyish olive-brown above without any warm tone and without streaking, and with a rump that does not contrast with the mantle: the impression is flat and uniform. The bill is long, fine and pointed, with an orange to pale flesh lower mandible that often has a dark tip; the forehead slopes away flatly, so head and bill together look long and rather pointed. The pale supercilium is clearest between bill and eye and stops just behind the eye; there is a narrow pale eye-ring. Underparts off-white with at most a faint dingy yellow wash on the flanks, far colder than on Marsh Warbler. The wing decides it: the primary projection is short, about half the exposed secondaries, with six tightly bunched primary tips. The legs are dark grey-brown, toes included. At rest the bird looks long and narrow, small-headed, with a long tail held up as it climbs.

Confusion species

Marsh Warbler is what it all turns on — see also the Marsh Warbler species page. Marsh Warbler is warmer and greener with a yellow wash on breast and flanks, has a long primary projection with seven or eight widely spaced tips, pale flesh legs, a steep forehead and a shorter, broad-based bill. Blyth's Reed Warbler is colder and greyer, shorter-winged, longer and finer in the bill, darker-legged, and shows a more obvious supercilium in front of the eye. Song separates them without fail as well: Marsh Warbler pours its imitations out in one headlong accelerating stream, Blyth's takes its time and repeats every motif two to four times with a short pause between. Reed Warbler has a warm rusty rump contrasting with the mantle and a short faint supercilium, and sits in reed standing in water. Paddyfield Warbler is smaller and warmer, with a short bill, a long supercilium dark-edged above, and pale legs.

Habitat

Damp scrub and tall herbage on dry ground, never reed standing in water: willow and alder thickets along streams and lake shores, woodland edges and clearings with nettle, meadowsweet and cow parsley, rank hedge banks, young birch regrowth, and in eastern Fennoscandia and the Baltic region strikingly often overgrown village gardens, park edges and the lilac and mock-orange bushes beside houses. What it needs is a dense herb layer with scattered bushes and saplings above it as song posts. The nest is slung low in the herbage or a bush, usually below a metre.

Range and movements

From eastern Fennoscandia and the Baltic region east through eastern Europe into central Siberia, with outposts in the mountains of Central Asia. Eastern Fennoscandia and the Baltic region have gone from almost empty to tens of thousands of singing males within a few decades, and eastern Scandinavia and the north of central Europe are being taken up in turn. All birds migrate south-east and winter on the Indian subcontinent, which is why they arrive only in late May and are gone again in August. Along the southern North Sea coast it is a rare but annual visitor: singing males in June on the Wadden islands and inland, and autumn birds at the coastal ringing sites.

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

How and when to look

The first half of June, between eleven at night and sunrise, on either side of the Gulf of Finland. Walk a village edge or a rank woodland margin and listen for a singer that repeats each little phrase neatly: that is the bird, and the song is more reliable than the view. If you do see it, go straight to wing and legs: short primary projection with six bunched tips, and dark legs. Anyone who hears a candidate outside the breeding range should record the sound before reaching for the binoculars — with this species that is the piece of evidence that counts.

Conservation status

Not threatened (LC) and one of the few warblers doing better across the board: the range has been shifting west and north for decades, and in eastern Fennoscandia and the Baltic region it has gone from a rarity to a common breeding bird. Neglect works in its favour — abandoned farmsteads, gardens left to run wild, rank stream valleys and young regrowth on clear-fells all deliver exactly the cover it wants. The pressures are correspondingly small and local: the clearing of scrub and rank vegetation, flail-cutting of ditch banks in June while the nests are still slung in the stems, and the loss of scrub in the South Asian winter quarters.

Scientific name

Acrocephalus dumetorum | Blyth, 1849

Blyth described the species in 1849 and placed it straight away in the genus where it still stands. The genus Acrocephalus was introduced in 1811 by Naumann & Naumann. Acrocephalus is Greek, from akros 'topmost, pointed' and kephalē 'head'; the Naumanns, who introduced the genus, called these birds Spitzkopf 'pointed head', so they read akros as 'pointed'. dumetorum is Latin for 'of the thickets', the genitive plural of dumetum, 'thicket'. The specimen the first description was based on came from India.