I used to work for a raptor rehabilitation center. This looks like a small hawk or falcon kill to me. It was probably a broadwing, red-shoulder, cooper, or a similar mid-sized hawk. The bigger hawks usually are mammal hunters, but will sometimes snatch a bird. The mid-range hawks are bird hawks. They will catch a bird, ground it, then pick open a single wound like this and eat as much as they can before a larger scavenger comes around. It really looks like a hawk kill, especially since I don't see bone damage, like you would expect from a dog.
With a cat, you wouldn't have the spread of feathers.
I'm sorry. She looked like she was a beautiful bird. There's little you can do about a hawk, especially the mid-sized ones. I would keep the others in under a wire roof for a while. A mid-sized hawk once it catches prey like this will often linger in the area to see if it is "prey rich" and target the others. If it doesn't find another kill as quickly, it will return to patrolling it's territory or continue migrating.