I don’t think a chicken would survive a bite with venom. Cooper heads are made to produce enough venom to than find their pray and swallow whole once the toxins have taken full affect. They can harm a dog, they are lower on the venom scale as a pose to a diamond back rattle snake. But there is still a great risk and if your dog is bitten, seeking a vet is recommended. I’ve always been told to stay away from copperheads and not to mess with them. The black snakes in the south? If it’s just black and skinny, can be a black racer.
best method to keep snakes away, is keep the area clean, reduce bushes, wood piles, and try not to leave grain that would attract mice. Also, snakes will eat eggs.
https://doggysaurus.com/can-copperhead-snake-kill-dog/#:~:text=Can a copperhead kill a dog? It is,and where the bite on the body was.