Unfortunately, I have seen that before, and I'm pretty sure it was a weasel..mink, marten, whatever weael-ish critter you have over there. They are notorious blood sucking little stinkers
They can't drag away the carcass, so they make a puncture mark, usually back of neck or head, and drink the blood and leave the bodies. A coon will try to take them with them and will also eat heads and tender vittles, and a fox woukd most likely eat at least one bird and try to stash the rest.
We've had problems with losing ducks to coons, foxes, and weasels, and by far the weasel did the most damage. Came through an inch wide opening in the duck hut and killed 13 ducks in one night(my mallard hen and 12 ducklings!) came back and got 7 more(my runners) the next night before we found the hole
I don't keep ducks anymore, needless to say. The chickens house is very well protected but the duck hut had that stupid tiny gap....
The coon would get one or two but leave the rest alive, and the fox got 2 out of the yard by the creek.
I HATE weasels; by far the sneakiest and worst predator I've ever had to deal with.
