Dear moron,
The birds at Wrigley Field always come around the same time of day. They come in and scoop up from the stands all of the leftover popcorn and other edible things to eat. The fans aren't throwing food anyway -- the birds are being smart and waiting on their free meals. This game started a little later than usual and went into extra innings making the birds a little more active than usual. Tune into another day game and I'm sure you see the same savages back at it.
Your loving Cub fan,
Guru