The Department of Conservation said yesterday it had "declared war on stoats" after the buff weka chicks, part of the department's breeding programme, were found dead on the island.
They were discovered by a Doc monitoring volunteer after he heard a commotion in the buff weka aviary early on Monday morning.
Doc breeding programme manager Stu Thorne, of Wanaka, said a stoat was found on Monday in a trap set alongside the aviary and subsequently destroyed.
"Stoats are killing machines and we consider them to be predator enemy No 1 of our native birds," he said.
The predator attack on the weka breeding aviary was the first recorded by the Stevensons Island programme.
Buff weka were transferred to the Lake Wanaka island in 2001 from the Chatham Islands as part of a Ngai Tahu initiative, in partnership with Doc, to re-establish the native South Island bird.
The weka are now established on the Doc-administered lake islands of Stevensons (Te Peka Karara), Mou Waho and Mou Taho.
Mr Thorne said it was likely the stoat had swum the 200m to the island from the mainland.
It appeared the 20cm-25cm long predator had gained access to the aviary by climbing up side wire and through the mesh roof, he said.
Two extra monitoring staff have been placed on the island and the area "saturated" with traps.
Stoats often hunted in pairs and staff were on the lookout in case another of the "ferocious" predators was still on the island, Mr Thorne said.
Stevensons Island has seven buff weka adults - three breeding pairs and a lone male.
The death of the four weka chicks was a "serious blow" to the otherwise successful 22-bird breeding programme, Mr Thorne said.
Buff weka
- Since 2001, more than 100 chicks have been transferred to sites after being bred at Te Peka Karara.
- An average of 25 juvenile chicks are raised per year on the island.
- Buff weka became extinct on mainland New Zealand in 1920.
- Stevensons Island is located in Lake Wanaka about 200m from the shore. This makes it susceptible to swimming predators.
- Stoats are one of the most dangerous native bird predators, known to swim up to 2km, and able to climb trees to target bird nests.
- Stoats were introduced in the late 1800s to combat rabbits. The voracious predator found native birds to be easier targets and has played a significant role in the extinction of several native species.
- Weka breeding manager Stu Thorne said the four chicks were not killed for food. One was mauled to death, and the other three died after bites to their necks.
