Hi Peter and Tony,
It is an adult male Swamp Harrier and not an adult male Papuan Harrier because on current knowledge Papuan Harrier in this plumage shows all dark (black) unbarred outer primaries, whereas Swamp Harrier shows clearly barred primaries. A Papuan Harrier in this plumage I think would also show a cleaner white underwing with less (possibly no) brown on the underwing coverts, a neater and more narrow black trailing edge to the underwing and a darker head. Swamp Harriers that look like the bird photographed aren’t seen that often but with more and more people carrying digital cameras they are being reported (and correctly identified) more frequently these days.
The original photo is here http://www.birdpedia.com/files/au/observation/Vic/jpg/7471551374_0001_0002.jpg
Cheers, Rohan
