I hate to quote wikipedia.. but I'm forced to do here
"The Federal Aviation Administration estimates the problem costs US aviation 600 million dollars annually and has resulted in over 200 worldwide deaths since 1988<SUP class=reference id=cite_ref-BSC-USA_25-0>[26]</SUP>. In the United Kingdom, the Central Science Laboratory estimates<SUP class=reference id=cite_ref-allan_5-1>[6]</SUP> that, worldwide, the cost of birdstrikes to airlines is around US$1.2 billion annually. This cost includes direct repair cost and lost revenue opportunities while the damaged aircraft is out of service. Estimating that 80% of bird strikes are unreported, there were 4,300 bird strikes listed by the United States Air Force and 5,900 by US civil aircraft in 2003."
link Bird strike - Wikipedia, the free encyclopedia
Also read that bird hit may cause windscreen damage
also this
"Cracks often are caught while the plane is on the ground. They can be terrifying when they happen in the air. The Federal Aviation Administration has records of 20 in-flight cracking incidents since 1982, 12 of them on commercial airliners. "
Link: The Mystery of the Cracked Airplane Windshields - ABC News