In my experience they've trained themselves to spot most kinds of food very efficiently, but false positives, combined with a lack of object permanence, remain a concern.

They have, i was eating subway was once. Had a huge seagull right next to be staring into my soul, which is polite as far as seagulls go. So i took a piece of lettuce out of the sandwich and threw it to him.

Just stared at me, he knew there was meat and he wasn't taking anything less.