The crocs we're talking about aren't fed with the chickens, they're just teased with them. Maybe one of them gets the chicken at the end, but there's very little on it. So cutting off their food supply is not an issue.

Oh, and crocodiles aren't prehistoric creatures. They're as modern as we are, they live in the 21st century. They may have started out 200 million years ago, but they have developed. You might just as well say that insects are prehistoric. It doesn't mean anything.