Conservation of calories has been one of the greatest things to changing my appreciation of birds in general. We all know we need to eat to live, but birds need about 1/3 of they're weight in food a day to stay healthy. Every flight is the equivalent to us doing an all out sprint, and every flight that doesn't leave them with more calories taken in than they put into the attempt leaves them in a worse situation. Too many misses and they may not have the energy to make another. It really changed my perspective on a lot of animal activity thinking about it that way.