Early signs point to a heavy seeding of beech trees in the Marlborough Sounds and Nelson Lakes National Park next autumn, with potentially disastrous consequences for native birds.
Department of Conservation spokeswoman Trish Grant of Nelson said heavier flowering than usual could lead to a mast seed year, fuelling an explosion in mice, rat and stoat numbers from next winter.
"DOC scientists will be tracking seed production and rodent numbers in coming months," she said.
Pest control specialists were working on contingency plans in case predator populations boomed next winter.
DOC scientist Graeme Elliott of Christchurch said signs pointed to a mast year at least as big as the one which wiped out a mohua (yellowhead) population at Mt Stokes in the Marlborough Sounds about 12 years ago and reduced numbers in the Eglinton Valley in Fiordland from several hundred to a dozen or so birds.
Friends of Rotoiti spokesman Peter Hale said rat and mice numbers in Nelson Lakes National Park would boom on the back of extra beech seed. However, the real problem was stoats which would thrive as as they fed on rodents before turning on vulnerable native birds such as kaka, kakariki and juvenile kiwi.
"All ground-nesting birds are also at extreme risk, so we have grave concerns for the future of the few kea and falcon that are clinging on precariously in the region," he said.
Increased predator numbers would mean more trapping for his group's small band of volunteers, and more members would be welcome.
DOC senior ranger Nik Joice of Nelson Lakes said a heavy beech seeding would be a bitter-sweet pill for kaka. Their infrequent breeding was triggered by mast events but they would be under siege as nesting began.
Parliamentary Commissioner for the Environment Jan Wright has called for increased 1080 poison use to control the plagues of rats and mice which could follow a mast year.
DOC spread 1080 baits from the air in the Tennyson Inlet and Ship Cove areas of the Marlborough Sounds this year to kill possums, rats and stoats which killed native birds and giant land snails.
Anti 1080 group Pelorus Protection Inc has suggested trapping as an alternative to 1080 at Kaiuma, near Havelock, but spokesman Richard Glover of Havelock would not comment when asked if this was going ahead.
- The Marlborough Express