Ferrets have killed four brown kiwis at Pukaha Mount Bruce in the past month, bringing the number of kiwi fitted with transmitters at the wildlife centre down to just seven.
General manager Helen Tickner said the centre will be doing a kiwi call count later in the year and is confident there are plenty more kiwi in the reserve including many females without transmitters.
"Without downplaying it, in an unfenced reserve at this time of year, it's not unexpected to have this predation, but it's horrible," she said.
"We've caught one ferret and we're pretty confident that we're going to catch the other culprit that is still in the reserve."
Mrs Tickner said all recently killed kiwi were "certainly over the 1.2kg mark, so at least 18 months old".