A large white heron with a long yellow bill, long dark legs and a very long neck. When breeding, the bill becomes grey-black and long filamentous plumes develop, mainly on the back. In flight, the white heron tucks its heads back into its shoulders so that the length of its neck is hidden, giving it a hunched appearance. When walking, the white heron has an elegant upright stance showing the extreme length of its neck. When resting it is more hunched with its head tucked in, making the birds appear more bulky. Important identification characters when separating white herons from other white egret species in New Zealand include overall size, relative neck length, bill colour and shape, and how far the gape (i.e. the corner of the mouth) extends back in relation to the eye. The white heron is the largest, longest-necked of the egrets, and the gape extends well behind the eye.