Hello,
excellent shot. Tfs!
Your bird is a juvenile/1cy Whiskered Tern. Please note:
- although difficult to judge=wishful thinking at its best, head pattern with an extensive patch centered at the seems to fit Whiskered Tern best. Anyway I agree with you, the bird has a "Marsh Tern" head-pattern.
- I think I can just make out the characteristic pattern on the tertials: yellowish-buff with a romboid black pattern
At least I need more pictures for confident ID, and I hope you can provide them (maybe in a larger format?)
But ID is not important here imo. What a stunning shot!