A Department of Conservation experiment with low density 1080 poisoning is paying off for one of New Zealand's most endangered birds.
In the Catlins Bush on the South Island's south eastern coast the mohua, or yellowhead, is enjoying one of its best breeding seasons.
Once found across New Zealand, mohua now only exist in parts of the South Island.
"It's brightly coloured, it sings lots, it's very active so it's a good crowd pleasing bird, it really fills the forest with noise and activity," says Department of Conservation (DOC) ranger Graeme Loh.
A quarter of the mohua population live in the Catlins Beach Forest so alarm bells started ringing last autumn when rat numbers exploded by hundreds of thousands.
It might seem the little birds are quite safe away in their nests, but unfortunately that is where the rats live too and the birds make for great eating.
"Every time a female tries to sit on a nest she gets eaten and her chicks and eggs get eaten, so we knew for a fact we were in trouble," says Loh.
To save the bird that features on New Zealand's $100 note DOC turned to 1080, applying half the normal amount over the mohua's 100 square kilometre habitat.
"If it hadn't been for the 1080 we'd probably be walking through a very quiet forest," says Sue Maturin from the Royal Forest and Bird Society.
The verdict is that is has been extremely successful.
Forest and Bird is convinced it would have been much worse without the 1080 and wants it used more.
"Until we can find an alternative then 1080 is the best bet," says Maturin.
Right now in the Catlins Bush it sounds a convincing argument.