Sedge warbler

The sedge warbler (Acrocephalus schoenobaenus) is an Old World warbler in the genus Acrocephalus. It is a medium-sized warbler with a brown, streaked back and wings and a distinct pale supercilium. Sedge warblers are migratory, crossing the Sahara to get from their European and Asian breeding grounds to spend winter in Africa. The male's song is composed of random chattering phrases and can include mimicry of other species. The sedge warbler is mostly insectivorous. This is a medium-sized warbler, 11.5-13 cm long and weighing around 12 g. It has a streaked brown back and wings, and pale underparts. The rump is warm brown and unstreaked, contrasting with the duller wings. The forehead is flattened, there is a prominent whitish supercilium, the crown is streaked with black, and the bill is strong and pointed. The legs are greyish. The plumage of the sexes is identical, although they can be told apart when caught for ringing by the presence of a brood patch or cloacal protuberance. Juvenile birds have dark spots on the breast. They can be easier to confuse with aquatic warblers due to an apparent pale central crown stripe contrasting with the darker edges. Other similar species include moustached warblers and Pallas's grasshopper warblers. The oldest recorded sedge warbler was a bird ringed in Finland which reached the age of 10 years, 1 month. The typical lifespan is 2 years. The sedge warbler was first described by Carl Linnaeus in his Systema naturae in 1758 (British ornithologists did not distinguish the species from the Eurasian reed warbler until the 18th century). The genus name Acrocephalus is from Ancient Greek akros, 'highest', and kephale, 'head'. It is possible that Naumann and Naumann thought akros meant 'sharp-pointed'. The specific schoenobaenus is from Ancient Greek skhoinos, 'reed', and baino, 'to tread'. It is a translation of the old Swedish name for the bird, Sävstigare. It is monotypic. The sedge warbler has a large range and an estimated Global Extent of Occurrence of 10 million square kilometres, with a large global population including between 8.8 million and 15 million birds in Europe. Data analysis by the British Trust for Ornithology has shown that fluctuations in the sedge warbler population stem from the adult survival rate, due to changes in rainfall on the birds' wintering grounds. Global changes in population have not been measured, but the sedge warbler's status is designated 'of least concern' by BirdLife International. It breeds across Europe and western and central Asia and is migratory. After feeding up post-breeding, they migrate quickly across southern Europe and the Sahara from August to September. Studies in Nigeria and Uganda suggest that sedge warblers return to spend winter at the same sites, year after year. All sedge warblers spend winter in sub-Saharan Africa, from Senegal in the west to Ethiopia in the east, and as far south as the eastern Cape Province of South Africa and northern Namibia. The route taken on the southward migration, and eventual wintering grounds, correspond to the birds' breeding grounds. Birds ringed in the United Kingdom and Netherlands are later found from south-west Iberia to Italy; birds from Sweden are recovered in central Europe and Italy; while Finnish birds are found in north-east Italy and Malta east to the Aegean region. Sedge warblers from the former Soviet Union take routes via the eastern Mediterranean Sea and Middle East. Loss of wetland areas for feeding on migration, and the expansion of the Sahara desert, pose threats to the sedge warbler's breeding population. Birds begin leaving Africa in late February, fatten up at wetlands before and probably after crossing the Sahara, and arrive in Europe from March onwards.