ARCTIC WARBLER at RSPB Bempton Cliffs Reserve on 5 October. An Arctic Warbler was reported at Bempton on 6 October in addition to the Greenish (Eastern Crowned and Yellow-browed Warblers!) leading to some discussion. These photos were taken when the crowds were first taken into the usually out of bounds field to see the bird reported as a Greenish.
I hadn't looked at my rather poor photos of it until later and they appeared to be OK for Greenish, with some pro-Greenish ID features like small dark spot on lores, pale feathering at base of upper mandible, diffusely spotted ear coverts, broad supercilium not narrowing behind eye, pale tip to pale lower mandible, whitish unstreaked underparts, uniform crown, c.65% primary projection vs. tertial length and tail projection vs. primary tips about the same length.
However, opinion seems to be Arctic now, especially having heard the call and it is generally thought that the Greenish and Arctic were one and the same all along. Surprising how tricky this one is, it does look very, much like a Greenish in some of these photos but it has the same primary covert pattern and greater covert bar of the bird that looks much more like an Arctic in flat light on the following days. The wings-open shot below seems to show emarginations to only three primaries (P3,4+5), which is mentioned as diagnostic for Arctic. The pale feathering above the bill is probably not extensive enough for Greenish but the broad supercilium behind the eye is still perplexing but maybe just a result of a particular stance? There are photos of clearer Arctics on the internet with pale tips to the lower mandible as well as uniform crowns, whitish unstreaked underparts and a similar pp to this bird.... so it looks like I need to forget some of the features mentioned above as exclusively for Greenish and this pair can obviously still cause problems to experienced observers. I commented at the time that the head pattern of these phylloscs changes with their stance and also the direction of light but please note I have rewritten this post in light of subsequent opinion. Please comment below if you would like to add to the debate! Thanks again to the finder Trevor Charlton and the lovely people at RSPB Bempton for looking after us.