The Department of Conservation (DOC) said the cause of death of the other two birds was still being investigated but 1080 poisoning was a possibility.
Takahē recovery programme operations manager Deidre Vercoe said what the team learned from the takahē deaths would be vital for informing them how to manage the recovery of the species in the future.
“The three takahē deaths are upsetting. We know that the aerial 1080 predator control will have helped protect other threatened species in the area from predation,” she said.
Vercoe said large-scale predator control was essential for restoring takahē to large wild sites and without it they would be limited to sanctuary sites for the foreseeable future.
The shared vision with Ngāi Tahu was to return this taonga to its natural landscapes. Takahē were released into the Gouland Downs area of Kahurangi National Park in 2018 to set up a second new wild population outside of the takahē’s Murchison Mountains homeland.
“One of the main reasons for choosing Kahurangi’s Gouland Downs to establish a second wild takahē population was the relatively low predator numbers which is primarily due to ongoing pest control,” she said.
DOC carried out aerial 1080 predator control over about 50,000 hectares in the Aorere and Gouland Downs area of the park as part of its Tiakina Ngā Manu programme to help protect threatened native species including kea, kākā, whio and great spotted kiwi from rats and stoats. It followed last year’s heavy beech seed fall that caused predator numbers to rise.
Post-mortem results on the takahē first found dead show 1080 was the likely cause of death. DOC was waiting for toxicology testing results before it could confirm 1080 was the cause.
Post-mortem and toxicology testing was still to be carried out to determine the causes of the deaths of the other two takahē although 1080 poisoning was a possibility.
She said three other Kahurangi takahē were lost to suspected predation prior to the 1080 predator control work. Another five died from other natural causes.
The Fiordland Murchison Mountains’ population lost an average of 15 per cent of adults from predation when stoat numbers surge following beech and tussock seeding, even with an extensive trapping network. Chick and juvenile deaths from predation are thought to be even higher.
Takahē had not been exposed to 1080 before, so their susceptibility to it was unknown. Research had been undertaken to find ways to reduce risk to the takahē. This included trials with wild takahē and non-toxic baits which suggested the risk of wild birds at Gouland Downs eating baits was low.
To further reduce the risk, a 587-hectare exclusion zone where no 1080 baits were applied was put in place to cover most of the takahē population. The exclusion zone was kept as small as possible to provide predator control protection for other threatened native wildlife.
Vercoe said the loss of the Kahurangi birds would not impact on the continued recovery of the species. The total takahē population had almost doubled in the past seven years to around 450 individuals and is expected to continue growing at 10 per cent a year. Takahē had moved from nationally critical to nationally vulnerable in 2017.