I can second what the others have been saying. They love fat.... so I was wondering how well chooks do eating fat. eg if you dumped a lump of mutton fat in front of them would they eat it and would they be ok?
Would they be ok? It certainly helps with their energy needs, especially in cold climates of course. But obviously it's no good for their protein needs, minerals, vits etc.
They certainly eat a huge range of things including meat and fish. In an 100 year old poultry book (Wrights Book of Poultry, 1910 edition) I read an account of a very large poultry breeder in England. They went through 2 horses a week for their chickens, bought from the knackers yard, butchered and boiled!!! That was primarily to meet the protein needs, with grains also fed and large grass ranges for greens.