Your best bet is to do a google search regarding fishers. they're vicious killers, and will even chase a porcupine up a tree and kill it by getting at it's belly. They will wipe out every cat in a neighborhood.What kind of hunters, what time of day, etc are fishers? Although we have lots of predators I don't worry about the possums, raccoons and owls, even weasels that are out at night when the chickens are locked up safely. Thankfully hawks don't appear to be the most efficient hunters. We've had several hawk attacks that resulted in no deaths or injuries. I sometimes wonder how the hawks survive.
Foxes however are a different story. They can hunt at any time and are cunning, and cowards Unfortunately they lean towards a sneaky smartness. If we can keep the foxes from getting the chickens, all is well.