Great Reed Warbler

Great Reed Warbler (Acrocephalus arundinaceus) is a very large, heavy-billed reed warbler with plain warm-brown upperparts, a pale eyebrow and buff-white underparts. Body shape, bill structure, plumage pattern and voice provide the strongest field characters. Age, sex and season may alter its appearance, so identification should combine several features and careful direct field comparisons with similar species in the same habitat (Wikipedia, general species account).

It breeds in western Palearctic reedbeds, clambers on strong stems while hunting insects and giving a loud rasping song, then migrates to sub-Saharan Africa for winter. Its movements and social behaviour vary through the year, with breeding birds generally more dispersed and non-breeding birds gathering where food is concentrated. Japanese records place it within the country's documented avifauna as a resident, migrant or visitor (Wikipedia, general species account; Wildlife of Japan occurrence records).