There are lots of differences in that version compared with the more traditional one(s). His surname is usually "Doolan", not "Duggan". The trooper firing the mortal wound is "Davis", without the "Fitz".

In particular the third verse doesn't ring true. Australia's grass lands are not known as "prairies" and there are no mocking birds. It seems to have been Americanised.

Perhaps "Australia" should be removed from the second verse?