Worst natural predator to the backyard chicken is the racoon! Then, the dog. Racoons can chew through "chicken wire" so if that is what you have, upgrade to hardware cloth, it's the wire with the little squares. You can nail/staple it right over your chicken wire. They'll also dig under coops so bury wire around the bottom of your coop if applicable to your style coop.
Oh, yeah- Everyone is right! Raccoons will gladly kill everything you got! However, easy to prevent it. 1-COVER THE WIRE whwere the roost poles are attached, if needed. If the chickens sleep up against the wire, raccoons will reach in and pull out any part of the chicken that will fit out. (Usually the head). You can use painted plywood or corrugated metal panels. 2- Don't use chicken wire! It is weak and useless against raccoons and stray dogs. If you already have it, overlay with good strong wire. 3- Make sure they can't dig in.4- Latch your door securely. They will try to open latches with their little, chicken-thieven' hands!
Raccoons killed every chicken I had in my coop in just one night. Worse yet, it was my 7 year old daughter who discovered the bloody carnage the next morning. That ended my chicken raising era for good.