Arctic Skua

Well, at least I think that is what this is. Not a great image, but hopefully good enough for someone who knows, to confirm the ID.

Definitely skua-like behaviour, from a high slow flight path it will suddenly drop low to the water, pick up immense speed, then chase and harass a tern till it disgorges food and the skua grabs the falling meal in mid flight.
Seen in the Tamaki Strait south of Waiheke Island.

Edit.....confirmed by 2 knowledgeable birders that yes, this is an Arctic Skua.