A photo taken in Nanning for your reference.
http://www.hkbws.org.hk/phpBB2/viewtopic.php?t=2170
In HK, as I heard, this species give a "chack-chack" call. Sound similar to Dusky Warbler, but harder and not difficult to detect the difference.
Looking at this photo, color tune at the cap and the mantle are no different, not like Japanese Bush Warbler which give a cap effect for its darker brownish head. I always think the population of Brown Bush Warbler are underestimated in Hong Kong, due to its secretive behavoir. It's not surprising to find Brown Bush Warbler, if it is, in Pokfulam.
Gary
