I had a full sized Dachshund that was terrorized by some bluejays for about 6 weeks. He came up with some tufts of hair missing on top of head and I had heard some unusual barking. I hid and observed that they actually seemed to be vying for control of his dry food bowl. They did the same diving attacks from behind.
I assumed this was how he had been pecked in the head. I heard him with the unusual barks one day and happened to be right next to a window to look out and see the bird peck him and then pull up from his dive and shoot (in a shallow ascent) right in front of the dog who snapped and very nearly plucked him from the air. He missed but did succeed in claiming a tail feather. I was pissed and had resolved to put food in the bowl that weekend and lie in the bed of Dad's pickup with an early 70's Daisy 880, waiting for a shot.

Two days later and before the weekend could arrive, I found a spot where it looked as though a bluejay had exploded. LOTS of feathers and a bloody, mauled carcass that was mostly coated with dead grass and barely identifiable. It was left in the sun out in the open. ​Evidently Icarus flew too close to the dachshund.

The jay's left the county to all evidence, similar to the OP's story.

I was so proud of him for taking care of business.