We do the same thing too here..not just bread but even rice and my Filipino dishes..If in case we fail to put the rest of the bread in freezer, the birds would be having a feast. I don't think it's a waste though as other living creatures would eat it Although I find it funny that these animals don't eat rice, when back in the Philippines, birds, cats, dogs, rats, etc. would..haha
I always feed the birds in my garden throughout the winter, and also have a big birdbath for them that I make sure is kept clear of ice. Our little friends need all the help they can get .