Albert de Jong
Larus cachinnans K:66B adult, April 23 2015, Ruse, Bulgaria. Picture: ringing group Strahil Peev.
Strahil Peev is a PhD student at the Institute of Biodiversity and Ecosystem Research of the Bulgarian Academy of Sciences in Sofia, Bulgaria. Breeding season 2015, Strahil and his collegues started trapping breeding gulls on rooftops of the city hall of Ruse. Ruse is situated on the south coast of Danube river in Bulgaria (60 km south of the Romanian capital). On the roof of this city hall, approximately 60 to 80 pairs of large white-headed gulls are breeding 2015. In Bulgaria Larus michahellis, Yellow-legged Gull is the (only known) breeding large gull. Until Strahil started trapping gulls in 2015! Strahil, with help from I Gabriel (who is a Spanish gull-watcher), found out that on this roof several Larus cachinnans, Caspian Gull are breeding too.
Huge bill with obvious gonys and very saturated yellow legs are pointers for michahellis. However, outer primaries completely wrong for michahellis, better fit cachinnans. From these images, grey tone of upperparts also too pale for michahellis.