Chickens can fly or more or less flutter up into trees.
We had a problem at one time with a raccoon that got into our coop. The chickens, one was killed. The chickens were so frightened they wouldn't go back into the coop.
I would come out at night and they would be all roosting up in these trees. They can't fly but they can flutter and get up high where they're safe. They can also fly over the fence.
When I first get new chickens, and sometimes you get some that want to explore the neighbor's yard, I clip their wings and so they can't fly. They learn that this is their yard and they stay here.
My husband left one of our little gates open last fall. I didn't realize a chicken went out. She stayed out all night long and boy, I got up in the morning and she was back and forth trying to get back in. They know where they live. They love their chicken house.