it looks too long-legged fo CG - see the one on the right of nr.5, which of course is a canus. see the hunched caspian 24 which isn't bigger but has almost the same posture. it seems there was quite some wind?
it may look like consuming attitude to go over so many ind. in a so undifferenciated way, but it is an exercise also and that's why i posted my suggested answers in advance. now if you like to compare and disagree..- most of them are not id-able with certainty but ~25% of them are.
my suggestions for the 32 marked ind. in pic 2, totally there are more than 70 gulls in the pic, the majority are caspians,
bold marked some ind. that are worth having a closer look (or at least to have a look at
1. cach 2cy
2. mich? 2cy
3. cach? 4cy? - are there tail markings?
4. cach? (bicoloured gr. covert pattern)
5. mich? although not much visible it seems to be very dark, possibly 3cy due to wide tertial crescents
6. mich? 3cy
7. cach? 2cy
8. mich? ad
9. cach ad
very small, fem type
10. cach ad mantle looks lighter than 9
11. cach 3cy - looks "high heeled", stiltish
12. mich? 2cy there's this strange red-brown surface at the wingbend, what is that?
13. cach 3cy (open wing). that light point in the outer wing looks perfect for a p10-mirror on setting. it is 2nd winter because of that mirror and the much paler inner primary window (extending on both webs), although in the whole wing there aren't any ad type grey feathers. also there are long pale tongues on inner webs in the dark outer primaries - which michahellis doesn't have so extended.
14. cach 2cy but could be mich (most 1st cycle michs have rather worn and thus plain greater coverts now)
15. cach 2cy(?) large and leggy, greyish scaps but tertials look 1st gen.
16. (twice) the ad one is square headed but could be both cach or mich
16. mich? 2cy dark head, well marked scaps
17. cach 2cy, look at those stilts. whole row of median coverts looks renewed.
18. cach 3cy
19. mich 2cy - this is the conspicous very dark ind. discussed in pic1!
20. cach? 2cy looks like casp but could well be a mich with pale underwing! threatening pose better for michahellis?
20. cach ad - twice again, this one is very strange, it has a really fat hanging bum but more in the middle (between legs), triangular head, all good for caspian but also it looks short winged!
21. cach? ad?
22.-24. nothing to see well
25., 26. and 27. look like adult michahellis (yellow legs, dark mantle);
27. is the dark mantled bird discussed in pic 1, darker than the rest of the ad gulls.
28. also prob. ad michahellis
29. cach/mich ad (prob. cach)
30. cach/mich 3cy?
31. leaning against the wind.., looks like mich
32. mich? 2cy
and the pic again for control. taken 8th febr. 08 in herastrau park, bucharest (cr. mihai)