An aerial 1080 drop is planned over 19,000ha at the head of Lake Wakatipu to control soaring rat numbers, stemming from the beech forest's ''mega mast''.
Department of Conservation (DoC) manager Geoff Owen said up to 15,000 seeds were falling per square metre, giving rise to predators which could potentiallyextinguish a local population of critically-endangered mohua, or yellowhead.
More than 1000 traps had been laid in the Caples, Dart and Routeburn valleys but due to the massive seed fall this year, more intensive protection was required, Owen said.
The ''mega mast'' had provided a bounty of food for native insects and birds, but also rodents, whose populations could expand rapidly, he said.
''When the seed runs out, they turn to our vulnerable species''.
Next month's 1080 operation was part of DoC's national Tiakina Ngā Manu (formerly Battle for Our Birds) programme.
Department of Conservation manager Geoff Owen. Photo / File
A second drop may be required this summer if rodent numbers rebounded quickly due to the massive amount of food available.
While the focus for this year's Wakatipu operation was to protect mohua, other species such as pekapeka (southern long-tailed bat), whio (blue duck), New Zealand robin/toutouwai and kākā would also benefit, Owen said.
