My windows aren't that clean.. so what's happening?

While I was typing the groovy bird eating broccoli post I heard a loud knock at the window followed by a thud to the deck. Poor little goldfinch! So far there have been no fatalities only very stunned birds. This one got placed under the potted tree until it recovered.
V was in her house when this happened, so I was able to go outside right away and pick the finch up. I washed my hands with lots of soap and hot water afterwards, got my camera to get these pictures then showered and threw my clothes in the wash. I'm not taking any chances with disease from outdoor birds and V.
Some days I have two or three birds hit the windows. Not all of them occur over the back deck, so I don't go looking for them. Poor little birds.