A friend of mine who is building a second RV9-A, had a bird take out about 85% of the front windscreen of a Cessna 172 while returning home on a cross country flight.
The "drag" increased dramatically, and it was tough to barely maintain altitude for the 30 mile return to the airport. He figures, that if it hadn't been a solo flight, that he would have had to make an emergency landing on a road, as it wouldn't climb at all with one person aboard.
Once over the numbers, out of habit, he pulled the throttle to idle, and the plane sank immediately for a rather hard touchdown, before a bit of power application could recover the sink rate!
L.Adamson