Here is some bird mass data.
I took the USAF strikes from the birdstrike web site, estimated the largest individual of each species (I guessed roughly if the bird was a small one, used several bird spotter web sites for the big guys, and rounded up to state the highest weight listed for the big guys:
www.s-92heliport.com/Birdstrike.xls
Note that the average strike was less than half a kilogram, and that the percentage of strikes 1 Kg or less amounted to 89% of all strikes.
Thus, the newest regulations:
Protect the entire aircraft against 100% of the areas struck
Protect for 89% of the strikes recorded
The older regulations (1.8Kg or 63 ounces) :
Protect 18% of the aircraft (the windshield)
Leave 82% of the aircraft unprotected
Protect against 94% of the strikes
So, in this imperfect world, we find that the old BCAR gives you protection for 5% more strikes on the windshield, but leaves the aircraft completely unprotected for 82% of the strikes A bad bargain, g33.