I don't doubt 9-15 million die each year from lead poison but it not by eating it, that they die from. It is from the lead pellets traversing their bodies, hitting important areas as they go. I have never cleaned a dove who has had a pellet which was not fatal and that they healed from it. I am sure a few might happen but not many. Most non fatal hits have to go through non vital areas or be so superficial that they rarely are retain in the bird. So even lead poisoning from pellet hits I suspect is a rare thing.

Evey consider the lottery odds of a pellet falling into an area that a dove will be eating? Probably have a better chance hitting the Powerball and Mega millions lottery the same week.