There was a little known study here in Australia regarding feral cats. The public view was that once they go feral they kill all our wildlife and must be hunted down and exterminated. They study showed that ALL feral cats resided around human habitation and in particular rubbish dumps. Thye would eat not just the rubbish but any other animal that was scavenging at the dump. Those that wandered futher afield we tracked and shot to examine the contents of thier guts. ALL the feral cats shot contained reptiles. NO birds, mammals or marsupials.