They do look simular to white brahmas. My white brahmas have more black feathers down the back.
Monster Chickens
I have a neighbor who raises coronation Sussex, as well as several other very large breeds. I think Porkpal is right, the hawks, and eagles size them up before attacking. The rabbits, and field mice are generally more acceptable to the predators. I love those large breeds and they are beautiful also...Hay...Donna thinking of you...