I'd never seen one on the farm, but after some research found out it was a Cattle Egret. They fly over from Australia in autumn to over-winter and are usually found around cattle and sheep.
A small stocky egret similar in size to a white faced heron, with a shorter neck and hunched posture. This is the smallest egret found in New Zealand and their numbers are dwindling after poor breeding seasons in Australia.
Another visitor to the farm is this white goose. We don't know where he came from but he seems to be enjoying the bull paddocks too.