I noticed this Yellow-vented Bulbul (Pyconontus goiavier) landed on top of my car one evening.
It then clawed it's feet on the upper part of the car's window and started pecking at the mirror image. It continued doing that for about one minute, enough for me to set-up my camera and fired a few shoots.
This burred image was taken from behind the front gate.
Birds are known to behave like this, thinking that those reflected images are their rivals and pecked it for a fight.
More articles and picture about the same behavior - Birds and their reflections - (from BESGroup website). Another interesting and nice picture of Ruby-cheeked Sunbird attacking the side mirror of WCMSusan's car here (from PhotoMalaysia.com).