ajohn

Interesting. I also saw this harrier today at Gei wai #8b, and I also concluded that it must be an adult female Pied Harrier. The pure white rump is another feature that does not seem to fit for Eastern Marsh Harrier.
This is not a plumage I am familiar with, and is quite different from the dark juvenile Pied Harriers that are seen more often. A very striking and beautiful bird!