I'm afraid the food supply is much grosser and problematic than we are accustomed to think. For a number of years I was partners in a theater company located in downtown Philadelphia, PA. On our block were a number of high end restaurants with rear access onto a shared alley way street. This is where trash was stored in dumpsters prior to regular pick up. Out there at night, rat packs at it non-stop. We loaded in props and costumes during the day. Walk around any big city (or rural town for that matter) when the foot traffic calms down, find out about the animals who share our space. Many years ago a friend of mine and I took a walk at night near the riverfront area in Pittsburgh, PA. Feeling something brushing against my legs. Guess what I saw. Lots of them.