I had a small spot on my wing and when I was done with the 3 step system it had removed it. Maybe the birds your way eat alot of acidic fruit, but really I know what you mean it was a b!tch to remove the spot. I went over it an extra time or two with the pre-wax with a firmer hand. If that doesnt help Mothers scatch remover will probably work, just dont scrub too much or apply too much pressure. Hope this helps.