In response, DOC is planning a winter aerial 1080 operation to control rat numbers in the Dart, Caples and Routeburn valleys. A second operation in the summer might also be required.
The controversial poison was the most effective way to knock down predators, Owen said.
More than 1000 traps in the Caples, Dart and Routeburn valleys had been holding the line for the small but important population, but with predator numbers exploding due to the huge amount of seed fall this year, more intensive protection was needed, Owen said.
The mega mast in beech forests was producing up 15,000 seeds per square metre.
"This provides a bounty of food for native insects and birds but also for rodents, whose populations can expand rapidly. When the seed runs out, they turn to our vulnerable species.
Other species such as pekapeka/southern long-tailed bat, whio/blue duck, New Zealand robin/toutouwai and kākā would also benefit from the reduction in pests, Owen said.
The pest control operation over about 19,000ha will begin during the first period of good weather after August 1 and take placeover two separate days. On the first day, non-toxic pre-feed pellets will be laid and about a week later the toxic bait sown.
Owen said all walking tracks within the control area would be closed during the pre-feed and toxic bait operations for up to one day each time, and deer repellent would be used with the 1080 cereal bait to minimise the risk to deer across all three valleys.