These were half buried in the grass. There was nearby few pigeon feathers too (I added them in the pile of larger feathers I dug up) but I think the ones buried could have been some other species (see picture 2). Possibly left there by goshawk.
Flock of starling sized birds either flew through/over central railway station or circled from the park other side towards N. Half of them out of the picture. Immediately followed by apparently jackdaws flying opposite direction.
Possibly same hawk followed.