For this bird, the lateral crown stripe and eyestripe is olive-green. It suggests that it is a Goodsons Leaf Warbler rather than Sulphur-breasted Warbler.
Another feature for Goodson's LW is the two distinct wing-bars. For Sulphur-breasted Warbler, the wing-bar is indistinct and you almost see only one thin wing-bar.
The colour of the underpart is variable between Goodson's LW and Sulphur-breasted W. For the identification of both species, head pattern is important for their ID.
Here is the Sulphur-breasted Warbler taken today at Tai Po Kau.
black lateral crown stripe
indistinct wing-bar
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