Helicopters have dropped two loads of non-toxic pre-feed bait over Stewart Island/Rakiura as a precursor to 1080 bait being released.
The pre-feed non-toxic bait prepares rats and possums to eat the 1080 bait.
Last year the Department of Conservation announced plans to drop 1080 bait to reduce the feral cat population endangering the southern New Zealand dotterel.
The population has declined in the past four years despite trapping and other efforts to reduce cat numbers.
Now there are about 105 birds left.
The bait will kill rats and possums which the cats will feed on.
About 108 tonnes of cereal bait containing 162kg of 1080 will be dropped.
Zero Invasive Predators (Zip) is working with Doc to reduce pest numbers.
Zip adaptive development director Courtney Hamblin said it was not known when the first drop of 1080 bait would be made.
"The timing of that operation will be determined by the length of time elapsed since the pre-feed, the weather that has prevailed since, and the rats’ breeding cycles.
"The operation will also require a window of calm, fine weather."
So far the operation had gone "very smoothly, despite Rakiura’s challenging weather".
