Thank you for an all too confusing post. I suggested using a piece of pure copper, not a penny which is copper-coated zine.
When copper oxidizes it does not form zinc, nope, it turns into copper sulfate, carbonate and chloride salts in varying concentrations.
Also, it would take a heck of a long time for the copper, any copper, to sit in water for it to do anything otherwise we would all be replacing our copper plumbing every two months. I am assuming that the good folks here on this thread are changing out the water in their bird baths at least every few days and not leaving it to sit for the months and years it would take for copper to oxidize IN the water.
If necessary, I will remove the post I offered if you think it is not accurate.
I already cleaned my bird bath today; I will go sit and put my feet up now.
