In the world of current technology of relatively inexpensive and quick DNA analysis, we sometimes forget that for many years an internal examination via surgery was the only way of telling (without laying an egg or fathering chicks) the difference between males and females of monomorphic parrots (“monomorphic” as being defined as both males and females have undetectable outward appearance differences). “Surgical sexing” as it is often called, is still done in many cases where it is important to know how healthy, mature, and active the reproductive tract is especially when the birds are being put with a mate for the purpose of breeding. At the end of this procedure, it is common for a bleb of tattoo ink to be instilled under the skin in the wing web. The general standard is that the ink is put in the right wing for males, and the left wing of females (“hens”).
Sometimes these tattoos can be mistaken for injury or bruising. Here is a picture of a wing web tattoo in the right wing of a macaw.