I spent 11-24 September of this year in Azerbaijan. The main aim of the trip was to study Caspian Gull in the core of its range, away from the hybrid zone(s). I arrived hoping to see only Caspian, but it soon became clear (based on adults) that other taxa were present. This of course muddied the water as far as the identification of the 1cy birds was concerned. With this in mind, here is a selection of the 1 cy birds present at Sijazan. To simplify matters, all are from the same 2 day period - in this context, note the different extent of moult and wear on these individuals.
I think many/most are Caspian but some I'm not sure about. Actually I have not had time to really work through all the birds, so I thought I would post them up here and share them. At the end are a few birds that are clearly not Caspian.
I hope you find the variability as bewildering as I do. In a post to follow I will put up images showing underwings.