Willow Warbler

Willow Warbler (Phylloscopus trochilus) is a small green-brown leaf warbler with pale underparts, a long eyebrow and generally pale legs. 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 through open birch, alder and willow woodland across northern Eurasia, catches insects among foliage, nests close to the ground and makes a long migration to sub-Saharan Africa. 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).