Staff at the Orillion factory in Whanganui have worked overtime for the past few months to supply extra 1080 poison bait for this "megamast" year.
A megamast year is when trees dump a large amount of seed and in New Zealand native beech and podocarp trees seeded heavily this autumn.
When that happens rat and stoat numbers increase and they turn to eating birds when the seed source runs out.
There were mast years in 2014 and 2016, and Orillion beefed up production. It has now reached a "new normal", chief executive William McCook said, and is half way through possibly its biggest 1080 bait production in any calendar year.
Its 15 staff have only just stopped doing overtime.
The Whanganui plant makes most of the 1080 poison bait used in New Zealand. A new Christchurch company, Pest Control Research has provided product for one aerial operation, but the facility has been off-limits since a staff member suffered from contact with a poison in late May.
WorkSafe is investigating.
Orillion has never had a serious incident, despite dealing with highly toxic materials.
"We are pretty proud of what we do and we believe we do a good job responsibly," McCook said.
Mast years happen when the average summer temperature is more than 1C above the previous summer's average, Forest & Bird says.
More are expected and Orillion's "new normal" is likely to continue.
It works with Landcare Research to find new methods, and has new deer and bird repellents ready to register. Its 28 products are sold into Australia, Asia and the Pacific.
Aerial 1080 operations are still the only cost effective way to manage predators in large areas of rugged forest, McCook said.
"There's nothing on the horizon at all internationally that will replace that any time soon."
But opposition to 1080 use has been building.
In April Orillion was first stop as about 100 anti-1080 campaigners moved around several Whanganui organisations as part of a nationwide protest over the use of 1080 for pest control.
Whanganui was the rallying point for protesters from around the North Island.
At the time, Sue Grey, a lawyer who acts for 1080-opponents, said here concern was the by-kill from 1080.
"It is not working the way it should be and everything is out of kilter in the ecosystems where it is used."
Department of Conservation's principle public adviser Herb Christophers said the organisation supported the use of 1080 while there was ongoing research to find a viable alternative.
"For 365 days of every year native species are fighting for survival and around once every three years 1080 is used to control predators in their habitat."
McCook said the big group of protesters who gathered outside Orillion on May 1 made their point while being respectful of staff.
Orillion is a state-owned enterprise, with government ministers as shareholders. The business is expected to make an acceptable return and all the money goes back to Government.