Originally Posted by Howard King
However Reed and Marsh warblers can be skulking or active, and when active in a feeding mode do flick wag and fan tails possibly for balance but it is behaviour seen often plus they regularly turn up in coastal halophytic vegetation especially if mixed with tamarisk as is the case in the location where AJ photographed this bird. We have ringed three or four Reed this week, I personally rule out this species with complete confidence on shape, size and colour alone even given the bad light in the pictures.
Don't know if this helps any but all adds to the picture.
I agree that we can also rule out both Marsh and Reed Warblers. The colouration of upperparts (they have also distinct edges, and a quite distinct greenish-olive tinge above in Marsh, whereas more warmer, often rufous-tinged above in Reed) and underparts seems to be wrong for both species. That kind of greyish upperparts match best for greyish Hippos.