Agree it's an Asian Brown Flycatcher - a 1st-Winter bird with retained juvenile feathers on the head and scapulars. Although Dark-sided Flycatcher regularly shows juvenile feathers on migration, "young Brown Flycatchers only exceptionally retain juvenile feathers on the upperparts." It's certainly a plumage I haven't seen often in HK and could be confusing.
The quote is from the paper on flycatchers by Paul Leader in British Birds November 2010 Vol. 103. A useful paper which includes a number of photographs by local HK photographers. Link to the article is:
http://britishbirds.co.uk/wp-con ... 8%E2%80%93671_A.pdf
David
