Now it makes sense. I was curious to know which UK falcon would actually be interested in chickens, let alone try to attack one.
Just had a look ,MWB and found there is only one NZ falcon and that is the Karearea. What a gorgeous looking bird! I do envy you being able to watch it.
It looks as though the female, weighing in in at 500 lb might be the culprit. A very large lady! This website does mention their preferred foods, but also mentions poultry :
http://www.hawk-conservancy.org/priors/nzfalco n.shtml