I have been doing a bit of digging into Green and Greenish Warblers following the bird on Bardsey two weeks ago. I have been in contact with Peter Kennerley (co author of the Dutch Birding Paper on Breen, Greenish and Two Barred Greenis) who has given comments on the bird. I have sent on the comments to Rich B who has done more 'stuff' on his blog and I have copied below. It may be that we are never able to ID the bird in question, as it appears to be at the extreme end of the range for Greenish and even within the bounds of Green. Any comments on this bird would be most welcomed!
Taken From Rich B's blog (Photos (c) Rich B
We've been given a few more pointers on the separation of Greenish Warbler and (Bright) Green Warbler. It's not going to help to secure the identification of our bird, but it does provide a few more talking points. The reason that Green Warbler has been suggested is due to the extent of yellow in the supercilium and ear coverts, which seems to be on the extreme side for Greenish Warbler, however see: http://birdsofkazakhstan.com/greenish-warbler-phylloscopus-trochiloides/ for photographs ofGreenish Warbler in South Kazakhstan (but different light conditions). The chin, throat and upper breast have a pale yellow wash in our bird, but this seems to be within the realms of Greenish Warbler.
A new feature to us (and apparently said by some to be diagnostic) is the possibility that the feathering along the lower edge of the eye is white (thus contrasting with the ear coverts) in Greenish Warbler and matches the colour of the ear coverts in Green Warbler. It is important that this is assessed in good light conditions so perhaps we can't look at it with any certainty using these photos. However it seems fair to say that our recent bird has feathering more concolourous with the ear coverts than the other two birds, but perhaps not to the extent expected in Green Warbler? The three photos below are full size so anyone out there who's interested can blow them up a bit bigger for a closer look. The lack of yellow in the wing bar seems to have no relevance as fresh Green Warblers on the Turkish Black Sea Coast can show white wingbars when fresh. Ultimately it seems that some extralimital, worn birds cannot be identified without DNA analysis or a sonogram.
We would be very interested if anyone out there knows about leg colour (which was surprisingly pale in this bird), or the patterning of white on the inner web of the outer tail feather which in this bird was as would be expected in Greenish Warbler.
The Bardsey Green(ish) Warbler (upper photo) clearly differs from our two other recent Greenish Warblers (middle photo 11 June 2010, lower photo 8 June 2012). (c) Richard Brown