I'm so glad you caught a photo of this bird! I was in Tsim Bei Tsui on Nov 23rd and could have sworn that I saw one as I was walking in the grass along the edge of the first two ponds on the right (past the first patch of mangroves) as you're heading down the hill from the police station. I didn't have a camera, and a couple other birders / photographers I ran into said that they had not seen that bird there in 4 years.
Is this bird common at Mai Po?