The Marsh Warbler (Acrocephalus palustris) is a plain, olive-brown bird that is virtually impossible to separate from the Reed Warbler by looks alone. It measures 13–15 cm, weighs roughly 10–16 grams, and shows uniformly olive-brown upperparts without distinct markings, creamy-white underparts with a yellowish tinge on the flanks, pale pinkish-brown legs and a rounded forehead. What sets this unassuming songbird apart is not its appearance but its extraordinary voice — one of the most captivating in the bird world.
A singing male delivers a long, energetic, flowing stream of whistles, trills and mimicry, weaving in the calls of dozens of other species — both the European birds it meets on its breeding grounds and the African species it has picked up in its winter quarters. The song is often heard late in the evening and through the night around midsummer, and together with its choice of habitat is the only reliable way to distinguish it from the near-identical Reed Warbler, which favours reedbeds and sings a flatter, more repetitive song. The Marsh Warbler breeds in southern and central Sweden, a range that has expanded northward in recent decades, with a population estimated at 50,000–100,000 pairs and increasing; it is absent from the mountains and the far north. It builds its nest low in dense stands of nettles, meadowsweet or other tall herbs, attaching it around several upright stems, and the female lays 4–5 eggs, incubated for about 12–14 days. As a long-distance migrant that arrives late and breeds late in the season, it usually raises only a single brood before departing for sub-Saharan Africa in late summer, feeding meanwhile on insects and spiders gleaned from leaves and stems, with a few berries added late in the season.
Read about this species in Swedish →