I think that Goodson's/Hartert's LW also warrants consideration in Vietnam. This is the commonest species from this complex wintering in south China.
Sorry, I don't have any further advice on which this bird is - it's a group that needs better understanding of ID features!
John, Ayuwat suggested Hartert's for a bird I saw at Hoi An in Dec 15, but the images I studied showed strong yellow tones, which didn't seem right for the bird I saw. It seems too yellow for this bird too. I know nothing about Goodson's. HBW suggests only that fokiensis might reach Vietnam.
John, hope I am correct in saying that the Goodson's, in Kowloon Park, have a much brighter yellow coronal stripe!
Sorry, perhaps some ambiguity and confusion from my post. Hartert's and Goodson's are both names for the same species, Phylloscopus goodsoni. There are two subspecies:
- nominate goodsoni, which is usually bright yellow below, sometimes approaching the colours of Sulphur-breasted Warbler (http://orientalbirdimages.org/search.php?Bird_Image_ID=69213&Bird_ID=2916&Bird_Family_ID=&Location=)
- fokiensis, which is whiter below (http://orientalbirdimages.org/search.php?Bird_Image_ID=104351&Bird_ID=2916&Bird_Family_ID=&Location=)
The problem is that, as far as I know, there seems to be no confirmed features to definitively separate fokiensis from claudiae (and possibly from reguloides subspecies) except song and DNA. For example, in Hong Kong all white-bellied birds are treated as fokiensis/claudiae, neither of which is confirmed in HK, although potentially both occur.
The subject bird in this thread is not nominate goodsoni, but I'm not sure that fokiensis can be conclusively ruled out, and the yellowish wash to the supercilium may actually favour that taxon over claudiae.
Thanks for this, John. With you now. This of course muddies the waters still further - the Hoi An bird I saw could have been one of three species then - assamensis Blyth's, Claudia's or fokiensis Goodson's. :eek!: