A5 is an interesting bird. It was first trapped on Pond #11 at Mai Po in January 2011, and remained there through March 2011, preferring to stay on the gei wai rather than in the bay with most other Avocets. It was seen again on Pond #16/17 in May 2011.
It turned up again on Pond #11 in February 2012 and has been seen there a few times since, again apparently preferring the gei wai to the bay.
As Katherine mentions, the two=-flag combination is essential to demonstrate that the bird was flagged in Hong Kong. We have had many overseas resightings of waders which can be recognised as HK birds by the white over yellow combination. We choose to use engraved flags for both colours partly because this allows the combination to be recognised even when one flag cannot be read (not an unusual occurrence).