A year or so ago, my velociraptors (chickens) killed and ate a black snake. It was about 4 feet long. This year they watched one of similar size slither across the yard, through the run, and over into a neighbor's yard.
Of course, I don't know about any smaller snakes that they might encounter in their daily foraging around and about. The chickens scratch about so much, it may keep the snakes at bay until nightfall.
A couple of years ago, I had a hen trying to brood at a time I didn't want chicks. I had been reaching under her and collecting any eggs she would sit on. So, THAT day, I reached under and felt something mighty strange. At first I thought she had an injured, swollen leg so I pulled her out...to find a rather good sized black snake sucking down an egg.
Snakes don't really bother me, but I was pretty put off by that whole experience.
I got a call at work this summer from my wife who was off and home. She was in charge of feeding my quail who was about 1 week away from laying. She was freaking out telling me I had to come home for lunch immediately! Snake was in quail cage. She is terrified of snakes, so I went on home right away. Found 5' long black snake in pen, 7 dead quail, and 2 were in belly of snake already. 20 other were scared to death and shaking like crazy. So, set me back on quail egg production needless to say. I killed the snake and thru in chicken pen and they finished him off! My mistake was had quail pen in grass to move around and give them something to do. Now they are on sawhorses for time being.