Ask a Poultry Farmer: Bird growers should fear the racoon, not the cougar
There will come a time when you start shouting, "Dadgum varmints!!!" just like Yosemite Sam.
Everything kills and eats poultry in a different way. Here are some ways I have seen in Wisconsin:
Pet dogs: They will attack, killing for sport and leaving what looks like a massacre.
Feral dogs: Usually only grab one bird and carry it off for food.
Cats: One mistake is leaving your chicks in the same room as Fluffy. To a cat, chicks are food usually until they are half grown. They also will eat eggs.
Rats: Will take babies and hide them so you don't realize they are missing. Rats also will contaminate the feed and the building.
Fox and coyotes: Usually they will just carry off one at a time but I've seen where they have killed several coming later back for the dead ones. We have had good luck leaving a radio tuned to an all night talk station.
Weasels: Take babies to half grown chicks. They are very small so they can get in a rat hole. Trappers use a wooden rat trap to catch them. Most calls I get about a weasel killing turns out to be a mink.
Cats have been known to kill weasels.
Mink: Particularly nasty. They seem to kill for sport and kill everything in the pen. They bite the neck or back of the head. Leading people to say the suck the blood, I don't buy that. I have seen they kill a litter of kittens. It's said that you only see they near water. Don't believe that. We live a mile from any water and still have a problem They can also can squeeze through a small opening. They have very strong jaws and can break certain types of wire with their mouths.
Opossum: Likes eggs and will take full grown birds. They eat them there. Also, they can climb and like to eat chicken feed.
Skunks: Interesting thing is they like to eat the intestines. You find the birds looking like were processed. They will gnaw on the carcass if they are hungry. You may find a lingering odor. I have read the skunks will not attack full grown birds. Don't believe it.
Raccoons: If there is a challenge it's the raccoon. They climb, dig and have little hands that can open things.
Don't use chicken wire on the outside bottom of your pen or tractor (moveable pen). This is most important for non-roosting birds such as meat chickens and waterfowl. If they crowd against it at night a 'coon will reach in, grab a leg and chew it off. For a roost for chickens I like to use a pipe for the roost. With a wooden roost the 'coon can walk on it to get them. It can't walk on a pipe.
I once got up in the night to dogs barking in a barn. I couldn't find anything until I looked up to see a 'coon hanging upside down on the rafters.
When a 'coon has been in the coop, you usually find just the skin and skeleton of the birds picked clean.
Hawks: Pretty easy to derail. Put netting over the run and don't free range your birds. If hawks are in your yard, the birds will just be gone.
Owls: They are normally nocturnal but I have seen them in the daytime, so use the same precautions as hawks. Make sure to lock your birds up at night. Owls have been known to go right in the chicken house. Some say a light keeps them away but I've seen them fly under a yard light.
Most animals can be live-trapped. Don't just take them a mile down the road and let them go. First, they will come back. Second, don't give some else your problem.
As always, post questions in the comment section.