You could even try feeding him just a small amount or half of what he usually gets in the morning and the rest late in the day. He might need something in the morning if he is older - I have always fed my dogs twice a day so I don't know.
I was just wondering how do the birds get his leftover food with him outside? Or does he go inside after he eats? Black birds are kinda piggy! They steal all the food out of my bird feeder!