If the bird poop has left a mark in the paint, which generally is a speckled, dull finish in comparison to the rest of the paint, you can try and remove it with the Auto Body Cleanser. This will work to further clean up and remove the mark as long as it's not too deep. Wash and dry the car, then apply the cleanser to an applicator pad as per its instructions, apply in a circular motion on the marks and surrounding area, leave to dry and then buff off and inspect. Apply a second time if required. Always remember to protect the paint after cleansing with Auto Body Wax, Lazy Wax or Fully Slick.
If the mark is still there after this, it will potentially need to be removed mechanically by a machine, which is usually best left for a professional detailer who has experience in the field with this sort of thing.