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.