How can I deter birds from eating catfood left outdoors?

I leave dry cat food out for some feral cats that visit my yard regularly. I started doing that so they would hang out and get rid of the snakes and mice I was having problems with. Now the starlings and blue jays are emptying the self-feeder. I have three bird feeders in the yard so it's not like the birds don't have seed to eat. I moved the feeder onto the deck beside the back door, and under a chair. I put a plastic owl in front of the chair and a ceramic cat next to it. That didn't seem to bother the birds at all. Any other suggestions?