Later in the day I set about a practice run with the Barn Owl pellets. I selected a medium sized one, gave it a quick soak (though it was pretty fresh anyway) and dug in with some dissecting needles and entomological tweezers.
I selected the darkest one from above, medium sized and fresh
Absolutely fascinating it was. I was hoping to find a skull and lower jaws to try and ID, but ended up with four skulls (though I only found seven lower jaws). The numbers of other smaller bones was ridiculous - no way I was going to make any effort to collect and separate them all. I just honed in on the larger and hopefully more identifiable bits. Trying to clean the massed hair/fur off of everything is a right pain - I just got it off enough to see what I had. I'd already searched the tinternet and found a useful guide to identifying the various bits. Here's a few shots of various bits I found (most can be clicked for big):
Four skulls - three voles and one mouse. The skulls are apparently often damaged/crushed.
Corresponding lower jaws.
This is a vole skull, identifiable by the zig-zag teeth.
The serrations running the whole length of the teeth confirm - this is a Field Vole.
The more normal looking teeth with cusps confirm this is a mouse or rat.
Removal of the teeth shows the pattern of the root sockets (marked with yellow dots). This pattern confirms it is a Wood Mouse.
Wood Mouse lower jaw.
A couple of hip bones, showing the socket for the thigh bone (femur).
A few lower leg bones (tibia/fibula).
Various thigh (femur) and arm (humerus) bones. Probably.
I need to have a better look to find/ID the shoulder blades and forearm bones. I did find some odd large round bones which I've since realised after looking again at the guide are 'ear capsule' bones which would be part of the complete skull. So, in one pellet I found the undigestible bits of three Field Voles and one Wood Mouse. Now to find some Tineid larvae in an older pellet?