The hunt for stoats on Aotea/Great Barrier Island is winding down, after no evidence was found of the small predator that could devastate the island's precious native wildlife.
And it was not stoats that killed rare pāteke/brown teal ducks in the area where the predators were sighted, a Department of Conservation officer says.
A full-scale hunt was launched following a report of two stoat sightings in early January.
A DoC and Auckland Council operation has used stoat detection dogs and a network of trail cameras, tracking tunnels and traps in an area of 200ha.
DoC's operations manager on the island, George Taylor, says in a report the operation is winding down although the incident is likely to be ongoing for several months.
"Regular monitoring of traps, tracking tunnels, cameras will be necessary."
"The surveillance completed so far has shown no evidence of stoat presence. If a stoat incursion is confirmed the incident will be escalated to target stoats with the goal of eradication."
The island was considered to be free of stoats when the sighting was reported on January 4.
"The informant witnessed a stoat crossing Medland Rd between the quarry and Mason Rd; this was followed closely by another stoat," Taylor wrote.
"Given this is the time of year when juvenile stoats would be dispersing, and the fact that stoats can cover a large range, the sighting prompted an immediate incursion response."
Stoats on the island would be devastating, Taylor told the Herald. "We've got lots of ground birds - banded rails - and we've got native skinks."
The DoC website says stoats are voracious hunters that thrive in many parts of New Zealand, from beachlands to forests and remote high country. They have had a significant impact on many bird species, including New Zealand dotterel, black-fronted terns and young kiwi. Easy prey for them include tree-hole-nesting yellowhead/mohua, kākā and yellow-crowned kākāriki, and they have been implicated in the extinction of several species, including the laughing owl.
Stoats can swim up to 1.5km to reach islands and float even further on debris.
Aotea/Great Barrier Island, about 17km from the northern tip of the Coromandel Peninsula, is a stronghold for the pāteke/brown teal, an endemic duck and New Zealand's rarest water-fowl.
Taylor's report said 12 pāteke were found dead in mid-January in the vicinity of the stoat sightings and several were sent for necropsy (animal autopsy). Preliminary results indicated no sign of predator attack.
He told the Herald he was certain that they were not killed by stoats. They probably died of an infection, possibly botulism, as they were near a stream that had become stagnant over the hot, dry summer.