Sakhalin Grasshopper Warbler

Sakhalin Grasshopper Warbler (Helopsaltes amnicola) is a large plain brown grasshopper warbler with a long graduated tail, pale eyebrow and subtly streaked upperparts. 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 dense grass and scrub in north-eastern Asia and migrates south, usually staying concealed near the ground while feeding on insects and giving a distinctive repetitive song. 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).