Having trawled through some old photos taken when I visited Kos in May 2008, I came across the above shot which I must've clearly overlooked at the time. All of the Yellow Wagtails I encountered during my week trip were Black-headed Wagtails (Motacilla flava feldegg), or so I thought! The above individual clearly fits a migrant Grey-headed Wagtail (Motacilla flava thunbergi) - click the photo for an enlarged image. All of this is personally significant as it's the first time I've encountered this race of Yellow Wagtail. The moral of the story - make sure you check any photos you've taken very carefully!