Owl pellwt containing a raptor foot

I found a pellet (I think a tawny owl's) containing a whole raptor foot of some kind. Do owls sometimes prey on small raptors? Or could it have been a buzzard pellet? It soaked from the weather conditions but quite fresh.

Sadly I dropped the pellet on the way home so don't have a photo!

It was c. 5cm long, dark charcoal grey but we have just had snow and a lot of rain. Found underneath a tree, contained fur and feathers also. The foot was pretty washed out white coloured, I assume from digestion?

The area is used by tawny, barn owls, buzzards, kites, kestrels and sparrowhawks for certain.

Anyone have info this kind of feeding in owls?

Thank you