[terc]

Great article, Thanks.
I've always believed that knocking a bird out of the air required a head shot or a shot that would break a wing bone or the spine in the neck area.
The wing bones of a bird are under a lot of stress while in flight. A nick from a pellet will cause the bone to break.
If penetration to the vitals area (heart) is the goal, I think the bird would fly a long way before it actually fell.