In South Island beech forests, rangers are collecting branches from the canopy of native forests to see how much food is around for native wildlife - and pests.
The signs are that the forest larder this year will be abundant, which means predator numbers will multiply rapidly to plague proportions.
The rat population, encouraged by the bounty of seeds dropping from the heavy flowering season, alone could reach 4 million.
This explosion in numbers of rats and mice, and stoats which kill rodents and devastate birdlife, puts native fauna in the firing line of introduced mammals. Come spring, swarms of hungry predators are expected to turn their sights on high-risk species such as yellowhead, kaka, kiwi, bats and kea.
Unless that is, the most sweeping aerial assault ever undertaken in New Zealand using the poison 1080 disrupts what ecologists call the "predator plague cycle".
Scientists say the Department of Conservation has no choice.
"In places that are not protected from predators, many of our iconic native birds, lizards, frogs, weta and snails will continue to decline," pest expert Dr Andrea Byrom of Landcare told the Science Media Centre.
"With the pest control plan outlined for the 35 sites around the country, these species will have a chance."
We have been here before. In 2000, during a similar "mast" (high seed production) year, a local mohua or yellowhead population was wiped out in the Marlborough Sounds and its numbers slumped in Canterbury, Otago, Southland and Fiordland.
Nationally, there are fewer than 5,000 of the little birds left. If they disappear from forests, they will be seen only on $100 notes.
DoC intends to drop some 650 tonnes of bait containing 975kg of 1080 on 500,000ha of native forest, most of it in the South Island. The targeted areas cover some of the country's most dramatic settings - and where high-value, backcountry freshwater fishing spots can be found.
The poison project, which DoC has branded the "Battle for our Birds", has largely been applauded, despite the controversial history of 1080.
Federated Farmers and Forest and Bird, two groups which often find themselves on opposite sides of environmental fences, have joined forces in shared initiative backing use of the poison, which has been subject to dozens of scientific studies.
The Parliamentary Commissioner for the Environment, Jan Wright, has twice reviewed 1080 and each time strongly endorsed its use.
Compared with alternative methods of nailing pests - trapping, other poisons or biological control - none, she said, "come close to replacing 1080".
Her last report concluded: "We are lucky to have it."
But one group, which claims the support of thousands, has serious reservations about the aerial bombardment timed for spring.
The NZ Federation of Freshwater Anglers has warned its members not to eat trout or eels from areas targeted by DoC because of a risk of 1080 poison in fish.
Federation president David Haynes said the warning to all anglers and customary harvesters was for at least a year.
Trout could absorb 1080 by eating mice which had feasted on 1080 bait - what is called "secondary" poisoning. And as anyone who had caught trophy-sized trout in remote rivers and streams knew, the prized fish could be full of mice.
Said Haynes, a former research chemist: "All I'm saying is do the research on the secondary poisoning of trout from ingesting small mice.
"We know they eat mice. We know that mice can tolerate a lot more 1080 than possums.
"All we're saying is test it guys for the sake of 100,000 anglers in NZ and overseas visitors. If you can spend $21m spreading 1080 then you can spend a bit on this research."
DoC initially scotched the suggestion, accusing the federation of making "alarming statements".
Landcare Research scientist Dr Penny Fisher, a 1080 expert, said she was not aware of any documented cases of massive secondary poisoning of trout and eels from more than two decades of aerial operations.
In the late 1970s, researchers force-fed trout with 1080 bait "to no visible effect".
Eels which ate 1080-poisoned possums in a later trial were found to have extremely low levels of the pesticide in their flesh, which passed from the animal in a few days.
Responding to the Waikato Regional Council, which had asked about the federation's warning, Dr Fisher replied: "Given all these factors and probabilities, some potential exists for people to be exposed to 1080 through catching and eating a fish from within a baited area within a limited period.
"However the likelihood of this exposure being sufficient to cause poisoning of people is very low."
On Thursday, after initially rubbishing the anglers' lobby claims, DoC agreed to a monitoring programme.
The department's deputy director general Kevin O'Connor said that scientific studies indicated that 1080 drops posed little risk to freshwater fish or to humans consuming trout or eels. He noted while research involving trout had not been done, studies on eels suggested that an 85kg adult would need "to eat more than 7 tonnes of eel meat in one sitting to have 50 per cent chance of receiving a fatal dose".
But he said that to reassure concerns raised by some anglers, the department had agreed to work with Fish and Game on a practical programme for monitoring the impact on trout of its planned 1080 operations.
Dr Fisher suggested that anglers and other users of areas where 1080 could be applied should stay informed about baiting operations and check with DoC before heading for their favourite spot.
She noted that online advice about pesticide use included information about buffer zones for taking and eating wild animals from operational areas.
"Anglers could choose to apply these to fish they catch," she said. "Or to limit themselves to only catch-and-release fishing in such areas."
NZ world's biggest user of 1080
This country is the world's biggest user of 1080. Each year we use about 80 per cent of world production in relentless attacks on pests including possums - which both imperil native birds and spread Tb among cattle - rats and rabbits. About 500,000ha - 2 per cent of land area - gets an annual dump of 1080. Since 2008, between one and two tonnes a year of pure 1080 has gone into baits for pest control work.
The poison, which kills mammals by shutting down the energy they need, is imported as raw powder from the United States, where it is made at a plant in Alabama.
In the US, use of 1080 is limited to its containment in collars fitted to livestock as a deterrent to coyote attacks. The poison collars release a lethal dose when the wild canines attack sheep by the throat but it is a costly form of stock protection and predator control. With a review of the poison in the US due in 2016, the future of the American manufacturer is uncertain.
Here the Government-owned Animal Control Products, which turns the pure poison into much diluted pesticide and sells it to licensed pest control operators as pellets or gel, does not at this stage see a need to make 1080.
The Wanganui-based company says its prefers to retain buffer stocks to protect supplies, rather than building a plant to make the poison. Besides 1080 products, the company makes a range of anti-coagulant poisons for possum control, which do not require users to be licensed, and which it exports to a range of markets.
The company, which did not return calls, said in its 2013 annual report that it held 7.67 tonnes of 1080 powder, which would appear more than enough to meet the increased poisoning operations planned for later this year and the next few years.
The "battle for the birds" project is scheduled to run for five years at a cost of $21 million, with a share of the budget going to Animal Control Products. The large-scale 1080 drops planned by the Department of Conservation should result in the poison maker turning a bigger profit and making larger returns to the Crown, as it is required to do as a state-owned enterprise.
The timing could not be better. Though it made $500,000 in dividend payments last financial year, the company's revenue was nearly a third short of its 2013 budget and its pre-tax profit of $610,000 was below its target of just over $1 million.
Chairman Derek Kirke noted in the report that the company faced a number of challenges, including a constrained domestic market "and the distractions of continuing anti-1080 sentiment".
The Environmental Protection Authority, which monitors 1080 operations, last year issued a five-year review of its use and called the poison "the only viable option to control pests in our native ecosystems and to control Tb".
EPA chairwoman Kerry Prendergast said the review backed up the findings of a similar assessment in 2007 that "the benefits of 1080 use outweigh the risks".