Auckland Council is pushing forward on its plan to drop 1080 near the city's water supply, and says it may even have to drop the poison more regularly.
The Hunua Ranges in South Auckland is home to two-thirds of the city's water supply, but also thousands of unwelcome rats.
The rat population increased ninefold over summer, resulting in tens of thousands of rats - the highest number in the ranges in more than 15 years.
Council biodiversity manager Rachel Kelleher said that justified the decision to drop the poison, probably in late July or early August.
She said the drop would happen then because there was less food for the pests, and also fewer people would be using the ranges recreationally.
Leading up to the drop, population counts would be conducted for some of the most threatened species, including kokako and Hochstetter's frogs.
A non-toxic bait will be dropped beforehand, so the rats are tricked into thinking the bait is safe. The poisonous bait will be dropped five to ten days later.
Two to three kilograms of bait will be dropped per hectare, about a teaspoon of which is 1080. The cost is about $10 to $25 a hectare.
The Hunua Ranges has the biggest mainland kokako population in Auckland.
Dave Bryden, field coordinator of Kokako Recovery Programme, said only about 10 percent of the ranges gets ground pest control.
He said the drop would be more effective than ground bait as it got the areas outside of the pest control area, where many Kokako live.
The drop was unlikely to be a one-off however.
To keep the ranges free of rats, Ms Kelleher said drops would need to happen more often. She said the exact time frame for that depended on which species was being protected, but it was likely to happen every three years, and in time that could expand to every four years.
Ms Kelleher said technological advancements, especially with traps, meant that 1080 might not be the only solution long term.
The council was currently talking to nearby landowners about the drop, and some had expressed interest in having their land targeted too. A decision is yet to be made on that.
It was also speaking to Watercare and the Regional Public Health Service to ensure the water supply was free from contamination.
It said it was watching police investigation into the 1080 poison scare with interest, and would provide them any information required.