LOL my killer chickens have had a couple of mice too! I found them freshly dead in the coop, and assumed they had died, but I guess the chickens were to blame for that too. I thought they were going to choke on the hummingbird.
I couldn't be more sure, I watched them do it. They shook it like a terrier will with a rat, and I took the sparrow off them to see what it was. They did the keep away thing too, like with a worm, and shredded the hummingbird between them.
They have plenty of food! Free choice, plus a coop...