Millions of dollars are needed to stop predators in New Zealand forests because breeding conditions are at a 45-year peak, a conservation group says.
Native trees produce an extremely heavy seeding in mast years and this boosts predator numbers.
When that abundant food source is gone, predators start to feed on native birds and other species.
Forest and Bird chief conservation adviser Kevin Hackwell said hot summers cause more frequent masting events - and the Department of Conservation has described this year as a mega-mast.
"We've had a few big ones recently and that's why we've been hearing about masting events... but this one looks like it's going to be potentially an absolute record setter," Mr Hackwell said.
This year, the Department of Conservation would need double the $20 million it normally has to keep native species safe, Mr Hackwell said.