Doug,
This is interesting behavior!
I have visited the park several times and seen a lot of ducks and swans but never this bird.
I am impressed that it would venture to eat such a complex geometrical shape, especially as it is covered with an exoskeleton armor plate articulated shell! I have seen sea birds drop these from a height on rocks and so smash them to get access to the meat. Is this bird going to do the same or do the odd pieces get somehow twisted off and swallowed without loosing the rest of the crab to another scavenger?
Asher