Bears. Our worst loses was "The Summer of the Bear" as I called it. It was the year that I ordered 40 new peeps to add to my flock of 12 and to add some roosters in. Well, once that group was free ranging we had to get started on a bigger coop and run, and we had a broody hen with no rooster, so we called and visited and came up with duck eggs.
The first hit was to the coop at night, early Spring, it was a small bear and he did a great job destroying the roof panel and reached through "fishing" for chickens on the roost. The girls were wise enough to jump off the roost and get away. Then we were outside with the shotgun in our underwear with a spot light. The whole roof was ruined and had to be replaced. A metal panel went over the roost and I booby-trapped the whole thing as well as put a few things to make noise if a bear bothered it again. There were a few more attempts, a few more shots at 2am in our underwear, but no loses. The big flock was still just peeps, but the bear didn't go to the greenhouse with the peeps, but the coop with the older girls.
Flash forward to happy mama hen and two baby ducks and a whole lot of chickens running around, midsummer. The first hit that we knew of was the mama and the baby ducks. The ducks were just dead in the middle of the yard and the mama was cleanly eaten about half way in the middle of the yard. All the predators in our area take the body away, they don't dine out in the open. The fox/coyote kills always leave a mass of feathers, this was clean. No feathers, no blood nothing. A cleaned out body, well, half a body. Also, all other loses we ever had were at night, dawn or twilight, not high noon!!
Every 5 days this happened. I lost my chosen breeding rooster, Basil with a few more hens, then again in 5 more days.
Our local bears up to that point never bothered us. I had to take the bird feeder down before the end of April each night, but other than seeing a giant black bear sunning themselves in the back yard, or just wandering through. We would be outside grilling and see them only 50 feet away under the apple trees in the fall, and always being careful of the bear poo in the field when walking the dogs. This year was different.
I started talking to neighbors, a mama and three cubs were trapped just 3 miles up the road by a christmas tree farmer. Two days before TWO bears were trapped over the mountain going through a dumpster. The same week I had sighted a mama and at least one cub while gardening. Once I saw the cub, I went in the house and took the dogs in with me. So it was clear, this many bears in such a small area was just too many bears.
I suspected the ones killing the chickens was a mama and cubs, due to the LOADS of poo I found in the middle of the yard and the various sizes etc. I was very tired of the game commissioners telling me "poo poo bears are only after your chicken feed, stop leaving it where they can find it." Now I had chicken feed accessible, 25+ pounds of it, and these bears were walking past the feed and killing the chickens!!
After losing so many, my husband took a vacation day on what would have been the next 5th day. We stayed out in the yard with the dog (just a pup back then) on a long leash, and he kept is shot gun near by. Around 11:30am the dog went on alert at the lower corner of the yard. He would stare into the woods, hackles up and low growling. Then he would go back to not caring. About 30 minutes later, same thing, only a slightly different place in the woods. This went on for about 5 hours, and the area he stared at changed little by little, and eventually circled the whole yard. Before dinner time we put on our muck boots and went for a walk across the creek towards the last area that the dog growled at. We could hear something in the woods in the distance, but never did get a sighting.
Well, the game commissioner did give us a bear trap, and in two weeks we caught a very irritated raccoon. I was so excited when I saw the door closed, I wanted to see the bear, but I peeked through one of the holes in the side to see a raccoon curled up asleep next to his donut stash!!! After that they took the trap because the bears were still tearing up the dumpsters over the mountain.
What finally brought everything to an end was our electric garden fence. We would find a LOT of poo in the garden, and when we found tracks, they always came from the same direction. Once the fence was hot we went around a baited it with foil and peanut butter. Anyone licking the peanut butter was in for a rude awakening. Not only did it keep out the deer, but ALL bear sightings, poo findings, and killings stopped. I think they were coming it, pooping in the garden and then turning their heads and thinking "hey there are some chickens to eat" and then turning right to come up to the coop and the yard where the chickens spent their day. After the fence went hot, they turned left and went back into the woods.
To date, bears have been our worst predator. We lost 10 or 12 hens and the two baby ducks that year. Since moving to a new house we have had fox loses, hawk loses and I think a dog killed a hen. We just found a hen, she had been attacked, but not taken. Two days later everyone is letting loose at first light. My husband saw white paws out the window under the pine tree, but never saw anything else. Once he got downstairs with the shot gun nothing was there, and no one was missing.
I'm knocking wood about racoons. I've had more visits from possums, but they are after the eggs that the girls insist on laying in the woods where I can't find them!!! We have a good coop and so far no one has broken in.

I hear racoons very close by, the kids see them on walks, very close by, but so far no issues. I think having a big dog helps!