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- Latin synonym: Abrornis proregulus
- Name also: Pallas’s Leaf Warbler, Lemon-rumped Warpler
- Family: Leaf warblers – Phylloscopidae
- Appearance: A small leaf-warbler, about the size of a Goldcrest. Distinctive markings include two pale wing stripes, bright yellow rump, orange-yellow eye-stripe and pale yellowish stripe on cap.
- Size: Length 9–9.5 cm, weight 4.5–7.5 g.
- Nest: In a tree, usually high up. Ball-shaped, made of dry twigs, plant fibres, moss and lichen, lined with grass, birch bark fragments, hair and feathers.
- Breeding: 4–6 eggs laid in June, incubated by female for 12–13 days. Fledglings remain in nest for 12–14 days.
- Distribution: Breeds in the coniferous forests of Southern Siberia. Nearest breeding areas to Finland are around the Altai Mountains. Seen in Finland in small numbers fairly regularly during autumn migration.
- Migration: May be seen in Finland between September and November, most often in October.
- Diet: Invertebrates.
- Calls: A cheerful “tsui”.
Pallas’s Warbler is as small as a Goldcrest, and looks like a small plump leaf-warbler. They have olive green backs with distinctive bright yellow rumps. Their dark green heads are clearly marked with a yellowish cap stripe and a brighter yellow eye-stripe. Their primary wing feathers are brown with pale edges. Their inner secondaries and tertials (large feathers at the base of their wings) have yellowish edges and two pale stripes run across their wings. Their underparts are pale yellowish. They have dark greenish brown legs, dark brown beaks with a yellowish base, and dark brown irises.
Pallas’s Warblers can best be distinguished from the similar Yellow-browed Warbler (P. inornatus) by the stripe on their cap and their bright yellow rump.