A rat plague in the picturesque Hunua Ranges is threatening New Zealand's biggest mainland population of the kokako and prompted Auckland Council to carry out a 1080 poison operation.
Tens of thousands of rats are thriving in the Hunua Ranges southeast of Auckland, reaching a 15-year high.
The rodents eat the endemic kokako eggs from their nests, and also pave the way for more pests, including stoats, possums and feral cats, which prey on adult birds.
The pest explosion has now resulted in "dismal" results for the 2014-15 kokako breeding season.
Every year, Auckland Council closely monitors six pairs of kokako in the Hunua Kokako Management Area (KMA), which provides an indication of the breeding success in the wider population.
"This year's results are dismal with no fledging success at all and, of even greater concern, signs that adult birds have been lost," said the council's biodiversity manager, Rachel Kelleher.
Monitoring this season was expanded to observe five additional pairs that have settled outside the managed area.
The growth of the kokako population in the KMA over the last 20 years has seen birds move outside the pest-controlled area.
"Unfortunately, four of the five pairs we've been following outside the KMA appear to be missing altogether," Ms Keller said today.
The booming pest population has led to Auckland Council today announcing it will conduct an aerial pest control operation using cereal baits that contain 1080 in late winter.
Franklin Ward councillor Bill Cashmore, a local resident and member of the council's political advisory group for the project, stressed the importance of a new pest management regime.
"Not only are we seeing treasured and threatened species like kokako affected by rats stealing from nests or adult birds predated by stoats, the wider forest is suffering," Mr Cashmore said.
"Take a walk in the ranges today and you'll see 'possum browse', which is our forest canopy being destroyed by hungry pests.
"These results are heartbreaking but it is reassuring to know that help is on the horizon."
• The kokako belongs to the endemic New Zealand wattlebirds (Callaeidae), an ancient family of birds which includes the North and South Island saddleback and the extinct huia.
• Dark bluish-grey with a long tail and short wings, it has a pair of brightly coloured, fleshy "wattles" extending from either side of its gape to meet below the neck.
• Kokako are renowned for the clarity and volume of their song which carries far across the forest.
• They protect large territories of 8ha by singing and chasing away invaders.
• They eat leaves, fern-fronds, flowers, fruit and invertebrates.
Source: Auckland Council