As it relates birds, lead is usually swallows with the mistaken identity of a small stone. Many bird species do this to aid on the breakup of food within the gizzard. Obviously, lead sinkers aren't small stones and so the birds suffer the effects of lead poisoning as the sinker remains in their gizzard. The reports I read are of a scientific nature and tell what is being observed among a certain population of loons and the effect lead is having on them. Strictly in relation to loons, I've never claimed that thousands of birds are dying due to lead poisoning. I've tried to impress the point that lead is just one of many issues facing the species. In arms of waterfowl as a whole I'll stick by the studies I've found, such as the The Wildlife Society one I posted here, that say that lead shot and fishing bans save a significant number of birds. You can agree or disagree, it's your thought processes.
In terms of the Gettysburg point. That Civil War battle was fought over 150 years ago. Everything that was shot out of a rifle, musket, cannon (most cannon shells were cast iron) has now either been picked up for a pretty cool souvenir or is buried underground after over a century and a half of sitting out there. I'm also willing to guess that the amount of lead weights in our rivers, lakes, and streams today far outstrips even the original amount of lead munitions discharged during Gettysburg.