Please tell me your not being an @$$ and shooting at and killing birds for no good reason other than you can. Or, is "birds" a euphemism for something else? If not I really would expect more from a boyscout; when I was a scout they taught us to respect nature.
I say practice and have fun on the real thing....There are plenty of species around that are invasive and ruining the indigenous bird populations and I for one feel good about taking them out. In my state we have Eurasian Doves and Starlings a plenty and there is no better practice then the real thing. I remember quite a few starlings that have fallen to my paintball gun when I had one since I was in a neighborhood and had no other means including a slingshot. I would watch my bird feeders and when the starlings came in driving away the chickadees and finches there was a 68 caliber liquid death ball at 375 fps on its way.