River Warbler
Locustella fluviatilis
This is a largish warbler. The adult has an unstreaked grey-brown back, whitish grey underparts, and a darker undertail, which has white feather tips giving a contrasting pattern. The sexes are identical, as with most warblers, but young birds are yellower below. Some birds can show reduced dark markings on the undertail coverts (caused by more extensive than usual white tips) and thus are closer in appearance to Savi's warbler than typical river warblers. However, they typically still have a streaked breast and more olive colouration on the upperparts.
ID text from Wikipedia, CC BY-SA 4.0

Taiwan Bush Warbler
Locustella alishanensis
The Taiwan bush warbler is about 14 cm (5.5 in) long and weighs about 10 g (0.35 oz). The male and female are alike. The head is dull rufous-brown, the crown having narrow dark tips. The indistinct supercilium and eye-ring are pale buff. The upperparts, from the mantle to the wings and tail, are dull russet-brown. The chin and throat are white, the lower throat usually having spots. The upper breast is greyish brown, and the lower breast and belly are white. The undertail coverts are dark rufous-brown with warm-coloured tips.
ID text from Wikipedia, CC BY-SA 4.0
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Play today's Daily BirdPhotos and recordings are credited to their authors under the licence shown. Full profiles: River Warbler and Taiwan Bush Warbler.