A newly long-term study reveals kiwi chicks located in a North Island forest are more likely to survive following the aerial 1080 operation, where the poison is dropped, to control pests.
The Department of Conservation says 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.
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.
"Stoat attacks are the leading cause of death for kiwi chicks and without pest control as few as 5 per cent of chicks survive to adulthood," Principal Science Advisor Dr Hugh Robertson said.
"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."
DOC say 142 radio-tagged kiwi were monitored throughout the operation and none were poisoned.
Results show that just over 50 per cent 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 per cent the year after.
In the following three years, before the next five-yearly 1080 operation, kiwi chick survival halved to 15 per cent, well below the 22 per cent 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 growing by at least 2 per cent, which is the target in our new Kiwi Recovery Plan, we needed to increase pest control operations to once every three years."
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 per cent and 30 per cent) when rat populations were low and dropping significantly after that (to 12 per cent in the third year and 9 per cent in the fourth and fifth years).