Kiwi chicks in a North Island forest are far more likely to survive following aerial 1080 drops to control pests, a newly published long-term study has revealed.
Department of Conservation (DoC) staff tracked hundreds of North Island brown kiwi and their offspring through four large-scale 1080 operations in Tongariro Forest over 22 years, in the first longitudinal study of its kind.
It shows unequivocally that using aerial 1080 to suppress possums, rats and stoats benefits kiwi, said DoC Principal Science Advisor Dr Hugh Robertson, who was part of the research team.
"Stoat attacks are the leading cause of death for kiwi chicks and, without pest control, as few as 5 percent of chicks survive to adulthood."
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The research showed that aerial 1080 pest control significantly improved the survival of kiwi chicks for two years before dropping off when rat and stoat populations began to recover to pre-control levels.
"The 1080 operations knock down all resident stoats and likely all ferrets too and allow kiwi to survive to levels that can build their population."
The researchers also monitored 142 radio-tagged kiwi through four aerial 1080 operations. None was poisoned.
Just over 50 percent of kiwi chicks in Tongariro Forest survived to six months old in the first breeding season after aerial 1080 treatment. That dropped to 29 percent the year after, then plummeted in the following three years before the next five-yearly 1080 operation.
Kiwi chick survival halved to 15 percent in that period - well below the 22 percent survival required to maintain the population.
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, DoC says.
The kiwi chicks were monitored until six months old. That's when they reach a size where they can fight off stoat attacks.
Breeding success of New Zealand fantail/piwakawaka was also examined over 11 years, with the results following a similar pattern to kiwi.
Fantail nest survival was highest in the first two years after a 1080 operation (at 25 percent and 30 percent) when rat populations were low and dropping significantly after that (to 12 percent in the third year and 9 percent in the fourth and fifth years).
Fantail survival was significantly better than in untreated areas in nearby forests.