Pallas's Leaf Warbler

Pallas's Leaf Warbler (Phylloscopus proregulus) is a minute green leaf warbler with a yellow rump, bold pale eyebrow, central crown stripe and two bright wing bars. 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 mountain forests from southern Siberia to north-eastern China, actively gleans insects from foliage and migrates mainly to southern China and adjacent Southeast Asia. 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).