The Department of Conservation believes a single ferret is likely to be behind the deaths of 11 North Island brown kiwi chicks found dead in a Waikato breeding centre.
Waikato Conservator Greg Martin says it appears a predator-proof fence around the enclosure was damaged and that may have been how the killer got in.
He says a ferret was found trapped in the reserve on Wednesday.
However, Mr Martin says until tests are completed, they cannot confirm if the ferret or a wild cat is to blame.
The chicks were being raised on a reserve at Karapiro, south of Hamilton, to be returned to the Tongariro Forest. Two were found alive.
Mr Martin says the deaths are a major blow to the national Kiwi Recovery Programme.
He says the department will learn from the experience and make sure it does not happen again.
He says over the last five years, 65 kiwi chicks have been raised successfully at the reserve.