Huh, I thought they were companion dogs for royals during the reign of King Charles of England. And of course, any dog can be a chicken killer, duh. Take a breed that is mild and not noted for having a high prey drive (which CKCS are very nice)--I certainly would not suggest a rat terrier, but I'm sure there are people that have them with chickens.any size dog can be a chicken killer. And Cavalier King Charles Spaniels are HUNTING dogs.