chicks disapearing

so, i’m back on here again…recently a lot of our baby chicks have been going missing and even some have been killed, but we don’t know what is taking them/killing them? We found one of our baby chicks with it’s head cut off and the rest of the body laying there. Then, one baby chick went missing...

I have 5 - 10 week old egyptian fayoumis and brown leghorns chicks who free-range. I've heard these breeds are suppose to be great free-rangers but some have died without any sign of sickness, attack, or anything. I let them roam around when I'm outside but if I turn my back for a few minutes...