20 cm long. I suspect from a Verraux's eagle-owl.
I'm pretty sure it was a robin, at least. Looks like the aftermath of a predation event.
Found in the front yard of a suburban home. There are several hawks in the area that are commonly seen targeting songbirds, so I believe it may have been one of them.
There are black and turkey vultures in this area. Not sure how to distinguish the feathers yet.