Also attached is a photo I took of one of the birds last March, it appears to have a smudge of black on the right P9 very similar to that in Mark's photos from today. Would love to know if these marks are genetic and there like a fingerprint each year or whether they can vary from year to year.
There are a few photos of previous birds available on Iris http://www.birdguides.com/iris/pictures.asp?mode=advanced&tx=672&sn=cardiff&rty=0&r=1&st=1&gallery=0&v=0 unfortunately as the images are only 640 pixels it's a bit difficult to get much detail on them. To me the photos of the 2009 and 2012 birds look remarkably similar to the bird Andy and I photographed this year and those of the 2010 like the bird in Mark's photos and mine and Jim Almond's from last March.
Interesting stuff, going to have to spend a bit of time down there and see if I can get some more photos!