In the first longitudinal study of its kind, DOC researchers tracked hundreds of North Island brown kiwi and their offspring through four large-scale joint OSPRI/DOC 1080 operations in Tongariro Forest over 22 years.
DOC Principal Science Advisor Dr Hugh Robertson, who was part of the research team, says it shows unequivocally that using aerial 1080 to suppress possums, rats and stoats (killed when they eat poisoned pests) benefits kiwi.
“Stoat attacks are the leading cause of death for kiwi chicks and without pest control as few as 5% of chicks survive to adulthood.”
“Our research shows that aerial 1080 pest control significantly improves the survival of kiwi chicks for two years before dropping off when rat and stoat populations begin to recover to pre-control levels.”
“The 1080 operations knock down all resident stoats, and likely all ferrets too, which allow kiwi to survive to levels that can build their population.”
“We also monitored 142 radio-tagged kiwi through four aerial 1080 operations and none were poisoned.”
Results show that just over 50% of kiwi chicks in the 20,000-ha Tongariro Forest survived to six months old in the first breeding season after aerial 1080 treatment and 29% the year after.
In the following three years, before the next five-yearly 1080 operation, kiwi chick survival halved to 15%, well below the 22% survival required to maintain this kiwi population.
Dr Robertson says the research supported DOC shifting in 2014 to a three-year cycle of aerial 1080 predator control in Tongariro Forest to help the kiwi population grow.
“Population modelling shows that to get the kiwi population to grow by at least 2%, which is the target in our new Kiwi Recovery Plan, we needed to increase pest control operations to once every three years.”
The study began in 1992 and monitored radio-tagged adult male brown kiwi as well as 207 kiwi chicks hatched in Tongariro Forest between 1996 and 2014. The kiwi chicks were monitored until six months old when they reach a size where they can fight off stoat attacks.
Researchers also looked at the effects on nesting success of New Zealand fantail/pīwakawaka over 11 years.
The results followed a similar pattern to kiwi with fantail nest survival highest in the first two years after a 1080 operation (at 25% and 30%) when rat populations were low and dropping significantly after that (to 12% in the third year and 9% in the fourth and fifth years).
Breeding success of fantails was significantly better than in untreated areas in nearby forests.
The study was published last month in Notornis, the peer-reviewed scientific journal of the Ornithological Society of New Zealand (also called Birds New Zealand).
Brown kiwi is one of five kiwi species found in Aotearoa. The main threat to their survival is being preyed on by introduced animals. Chicks are killed by stoats and feral cats, while grown kiwi are most at risk from ferrets and dogs.