Birds Vs Window Glass

Last weekend I had 3 birds crash into the windows on the south side of my house. This weekend I had another two birds fly into the glass. What is up with these bird accidents? Is it because the woods are bare of trees and the sunlight can pierce the woods and reflect off the glass? Are the birds getting drunk from eating fermented berries or apples? Here is a picture of a little black capped chickadee on my deck. It's hanging onto a maple leaf. I didn't think the picture was very dignified. I hope no one takes my picture unconscious, on my back, with legs splayed apart.

I picked up the maple leaf so I could get a better picture. That bird had a death grip on that leaf with it's left foot. I picked up the leaf. The chickadee is so light he or she came up with the leaf without me noticing. I dropped the leaf and the poor bird flumped on the deck. Poor thing had it's bell rung twice. Ten minutes later the chickadee sat up, shook it's head, and flew off.