Early indications from the Department of Conservation (Doc) suggest that 2016 will be another beech mast year, in which seeds from flowering beech forests fall to the ground, attracting large numbers of rats and stoats.
The last mast, in 2014, was a one in 10-15 year event, and led to rodent invasions in Arthur's Pass and Nelson City. Masts typically occur every two to six years.
Doc staff have been assessing the likelihood of another mast, and say there is growing evidence that another big one is incoming.
"It's looking like in most places, there's a reasonable seed fall happening," said Doc scientist Dr Graeme Elliott.
"Over most of the country it is either patchily seeding or heavily seeding. It's probably going to be rather similar in magnitude [to 2014]."
Over the summer, beech forests gleamed with red flowers, which is the first sign of a mast.
In the past week Doc staff have been shooting beech trees to confirm seed fall – they found that although some areas, such as Marlborough Sounds, did not have much seed fall, seeds were evident across most of the country.
The scale of Doc's response would depend on if rats and stoats swarmed to feed on the seeds, Elliott said.
"What will really decide what we do in terms of pest control are what the rat, mouse numbers are like in May.
There's certainly the potential for some big rat, stoat plagues but we won't be able to confirm that until May."
Ad FeedbackControversy met Doc's response to the last mast, in which it dropped large quantities of 1080 throughout the country.
Doc's use of the poison – which is supported by the Green Party, Forest & Bird, and Environment Commissioner Dr Jan Wright, among others – is deemed to be cruel and unnecessary by some.
1080 is banned in many countries including the US. It kills most of the wildlife which consumes it, including the native birds it is intended to protect.
During the 2014 operations, four monitored Kea were killed by 1080. It is unknown how many un-monitored kea were killed.
About 25 monitored rock wren also disappeared, although it could not be directly attributed to 1080.
West Coast farmer Mary Molloy, of the Farmers Against Ten Eighty group, said it appeared Doc were over-inflating the threat of beech masts to justify its drops.
"The beech mast was inflated for the last operation – it didn't eventuate. There were some areas with reasonable masting, but the bulk of the country did not mast as they thought," she said.
"It's a decision that's made some time earlier, and the beech mast is largely an excuse, and often not verified."
The drops in 2014 had resulted in the deaths of numerous native birds, particularly kea and rock wren, so she was surprised more operations were likely.
"Their continued use of 1080 has reduced kea numbers to levels they will probably not rebound from."
Founder of the Ban 1080 political party, Bill Wallace, has also warned that more "unnecessary" drops were likely.
Elliott said 1080 would likely be used again this year, as it was still the most effective method of pest control.
"It's certainly the best tool we've got. It does a really good job on rats and possums, and it secondarily kills stoats, because they eat the rats.
Despite killing some threatened birds, the last drops were hailed a success, and killed about 90 per cent of rats while saving the lives of numerous native bird populations.