[order] Passeriformes | [family] Sylviidae | [latin] Acrocephalus palustris | [UK] Marsh Warbler | [FR] Rousserolle verderolle | [DE] Sumpfrohrsänger | [ES] Carricero Políglota | [IT] Cannaiola verdognola | [NL] Bosrietzanger

Bosrietzanger determination

copyright: M. Mark Swan

Medium-sized, quite heavy, rather pear-shaped warbler, with relatively long wings. Plumage varies with wear from bright olive-green to dull grey-brown, upperparts little marked except by fairly distinct pale fore-supercilium and eye-ring and bright fringes to tertials and primary-tips. Underparts yellowish or cream, with pale fore-face and wide bright pale throat often contrasting with olive suffusion on side of breast and flank. Legs pale and bright. Sexes similar, some seasonal variation.

Breeds in west Palearctic mainly in cool temperate middle latitudes, continental except in Englandand northern France, and largely lowland, although breeding in Switzerland up to 1500 m. Prefers damper and ranker sites, tufty, and fairly tall herbage, especially nettles, meadowsweet, willowherb, loose strife, wild rose and other woody or even be overshadowed by taller trees or bushes.

Acrocephalus palustris is a widespread summer visitor to central and eastern Europe, which constitutes >75% of its global breeding range. Its European breeding population is very large (>3,200,000 pairs), and was stable between 1970-1990. Although there were declines in Germany during 1990-2000, other populations increased or remained stable—including the key populations in Poland, Romania and Russia—and the species probably remained stable overall.

Chiefly insects and arachnids, with some snails and rarely berries in late summer and autumn. Feeds by gleaning from vegetation in grass and shrub layer, also sometimes from lower branches of trees. In herbaceous vegetation often perches on dead stems, rarely hovers to pick off items, and occasionally flies up vertically to take insect

This species has a large range, with an estimated global extent of occurrence of 1,000,000-10,000,000 km2. It has a large global population, including an estimated 6,400,000-14,000,000 individuals in Europe (BirdLife International in prep.). Global population trends have not been quantified, but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e., declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as Least Concern. [conservation status from birdlife.org]

Breeds May-July in West and Central Europe. Nest site is built in tall, often dense vegetation, aslo low to medium scrub. Nest, cylindrical, sometimes tapering, cup of leaves and stems of dry grass and other plants, with more compact lining of finer material, plus hair and some plant down. 3-5 eggs are laid, incubation 12-14 days, by both sexes.

Locally common summer migrant of western Eurasia, from southern England, southern Sweden and southern Finland east to central and southern Russia, and south to the Alps, Italy, Greece, Black Sea, eastern Turkey and Iran. Winters in subtropical to tropical eastern and Southeast Africa. (Baker K 1997) Summer visitor central, east and south-east Europe including isolated localities in south UK, south Scandinavia, European USSR, Transcaucasus, east Turkey; winters east and south tropical Africa. Migrant Cyprus, Near East, Egypt. Scarce migrant/vagrant UK (outside breeding areas), Eire, Iberia. Vagrant Iceland, Faroe Is., Balearic Is., Norway (outside breeding areas), Sardinia, Malta, Kuwait, north-west Africa, Madeira. (Parmenter T Byers C 1991)