I had this problem a couple of years ago. I have 50 acres, I would be walking around with my chickens, my ducks and my 2 cats and a chicken would be missing. No feathers floating no noise nothing. Day after day it happened, finally put up some borrowed video cameras and found it to be a Coyote stalking us. I would never hear a sound and it would just pick a chicken off. My bother came, sat on my porch when the Coyote approached the line of us he shot it. I still had hens completely disappear, so until I could afford to change what I had I bought 20 hot pepper powder and spread it around my coup and small fence area. That helped. Then I made a 100x100' run, dug trenches put in cinder block and concrete. Put up heavy duty horse small hole mesh (chickens can't get their heads out of the smallest square size), on the sides and top, attached electrical horse fabric (they come in different widths, I chose the widest). I securely attached that electric fabric on top and around the sides. Heard a few yelps outside at night, but I have not lost a chicken to coyote, fox, hawks or coon since. Kinda over-do? I love my animals, it's my responsibility to keep them safe. I've always felt, if you get angry for loosing an animal, domestic or farm kind, it's your own fault for not doing your home work, before I did the overhaul, it was my fault. I had been raised on a farm, but was naive when it came to having my own.