The Yellow-browed Warbler or Inornate Warbler, (Phylloscopus inornatus) is a leaf warbler which breeds in Asia east from the Urals to China. This warbler is strongly migratory and winters in southeast Asia.
This is an abundant bird of lowland and mountain woodlands. The nest is built in a tree. Like most Old World warblers, this small passerine is insectivorous.
There were formerly considered to be three subspecies, but humei and mandellii are now split as a separate species, the Hume's Leaf Warbler (Sangster et al., 2002) based on differences in morphology (Shirihai & Madge, 1993), bioacoustics (Alström & Olsson, 1988; Irwin et al., 2001), and molecular characters (Irwin et al., 2001). The Western Hume's Leaf Warbler's range overlaps with that of the Yellow-browed Warbler in the western Sayan Mountains (Ernst, 1996), but the species apparently do not hybridize (Irwin et al., 2001); the two species diverged roughly 2,5 mya ago (Irwin et al., 2001).
This tiny warbler is prone to vagrancy as far as western Europe in late September and October, despite a 3000 km distance from its breeding grounds. For example, this species occurs in late autumn in Great Britain regularly enough that it is not classified as rare there.
This is one of the smallest warblers, 9.5-10 cm long, and shares greenish upperparts and off-white underparts with typical leaf warblers. However, it has prominent double wing bars and long supercilia. The only real possibility of confusion is with Hume's Leaf Warbler, which has duller colours, a faint second wing bar and dark legs and lower mandible, in the limited area of overlap; their vocalizations are clearly distinct.
This bird is not shy, but its arboreal life style makes it difficult to observe. It is constantly in motion. Its song is weak and high pitched; the call is faintly disyllabic.