Owls along with quite a few other birds produce pellets. These are the indigestible bits which we would not eat but the poor old Owl, without the benefit of a knife and fork has to eat what it captures all in one.
So bones, feathers, fur and outer parts of insects all go down with the softer more digestible bits. In its stomach the protein and fats get broken down but not the bones and other tough bits. These are squished up into a neat package and ejected or sicked up out of its mouth.
Herons produce pellets and they contain fish bone and scales along with fur and feathers because they do not exclusively feed of fish. Birds of prey produce pellets although they are more selective in what they swallow but inevitably some small bones and fur or feathers do get consumed. Even birds like Shrikes will eject the tough outer skin or exoskeleton of insects which they have consumed.
I collected some Owl pellets down the lane from our house near Charroux in Vienne France. They were quite large so could have been from a Barn owl or Tawny Owl, I have even seen a Long Eared Owl in this region but only rarely.
If you soak the pellet in a shallow bowl of water, then you can pull it apart and tease out the bones and other more solid bits and leave fur and any feathers behind. It is amazing what you will find. Each pellet will normally contain several skulls, these are often broken up so you get 3 or more bits from each skull. The lower jaw is normally in two parts, and the upper jaw may have parted company from the skull.
Carefull examination will reveal loads of tiny bones, some will be vertebrae from the back bone and others will be bones from the feet.
This is a good activity for a rainy day when you have children or grandchildren at a loose end. You will need to have collected some pellets in advance obviously. They are to be found in outbuildings where owls roost or nest but also under large branches of trees where the owls might also sit either at night or during the day.
You do need to make sure they wash their hands afterwards because generally I have found that after an initial bit of reluctance because it looks a bit like poo, they soon get well into it and dispense with any pins or forceps you might have provided and use their fingers.