Hi steve,
Whilst it is certainly tempting to try and pull features out of this video that are concrete and not lighting affected...i am not sure that it is entirely possible. Unfortunately the distance and resolution are just too large a factor to yield anything for definite.
Though if i do give in to temptation, and after having scrutinised the video frame by frame, I do think there are MAYBE features there which are interesting, I think the spread wing looks interesting, with a darker secondary bar present, the tail, brief glimpse though it may be seems to match the primary coloration and the rump seems well barred.
I personally think it looks reasonably similar to the galway thayers in structure, dumpy, short legged, but again very difficult to discern for definite.
And some thayers do look "blotchy" as opposed to the darker slate birds. Im not sure that that is enough to eliminate it on this video, which is heavily affected by reflected light.
Either way, this bird should probably be followed up on, if only to nail it.
Again I am not saying it is thayers based on that video.
Just that its interesting enough to warrant a closer look.
Owen
http://1.bp.blogspot.com/_lZfSFoZeDLc/Su8wL6C4LNI/AAAAAAAACAg/GAtH1JW14uQ/s1600-h/Thayers+Gull+3.jpg