Were you using those chickens for bait? Fox will definitely kill a chicken. But he normally kills one and takes it with him. If you had several chickens killed and heads were missing and crops eaten you might need to start looking for a coon as the culprit. If there are bunches killed and just necks bitten it’s probably a weasel. Everything likes to eat chicken...I’m just saying the fox may not have been your culprit.