What killed them?

[WildfireSmitty]

Sounds like a mink or weasel to me, they like to just drink the blood and leave the rest behind. I have dealt with minks on a number of occasions.

 

[Herdsman01]

I agree with the mink/weasel idea, thats what it sounds like. We lost our entire flock to weasel in one night. We kind of had the same deal, no dismantled bodies, chickens just laying all over the place most laying on their backs, very few marks on the bodies (some had heads missing and were bloodier than others). Weasels are also known for killing for fun and not eating any of the bodies.