I had a similar thing happen to me a couple of weeks ago. A mink got into my duck house through an opening about 1 1/2 inches wide and killed 12 of my calls and also got into a cage and killed some of my lavender orpington chicks. I know it was a mink because it just went for the back of the neck and it was a bloody mess. And it came back the next night to kill my adult lavenders. I just happened to walk outside (before dark) and found it with one of my roosters pinned down by the head. I sent the dog after it, but he didn't catch it. Mink have a terrible smell to them (similar to a ferret). I could faintly smell it the morning after my ducks were killed and the second night it was very strong because it was fresh. They like to stay near water, so if you live anywhere near a lake, river, stream etc. it was likely a mink. They are hard to catch, but you should be able to catch it by putting dead animal in a live trap. They will not eat rat poison they like fish, small animals and birds. I haven't tried to catch the one that killed my birds, though I do see his tracks in my yard so I know he comes back.