Researchers have been monitoring a sample of 45 kea between Arthur's Pass and Lewis Pass east of the main divide since 2019, and any that died were retrieved to determine the cause.
DoC science advisor Josh Kemp said results from the first two years showed a sharp increase in monitored kea being preyed upon in the years, following the massive beech-seeding event in 2019.
"Just 6 per cent of the monitored kea were killed by predators in 2019, but this jumped to 40 per cent in 2020, most of which were eaten by stoats and feral cats.
"Kea are strong flyers but spend most of their time on the ground, foraging for food and roosting, which is why they are so vulnerable to predators."
Kemp said the new research was providing valuable evidence about threats to kea east of the main divide, which would inform future predator control strategies.
DoC controlled predators over about 40 per cent of kea habitat on public conservation land through its Tiakina Ngā Manu programme focusing on rats, stoats and possums, which leads to increased kea nesting success and chick survival.
Work was also under way into potential new tools for the control of feral cats.
Analysis of the dead kea showed stoats and feral cats killed 13 birds. Stoats were responsible for about half of those deaths and cats the other half.
A survival rate of just 60 per cent of adult kea is very unhealthy for the population and was concerning to conservationists.
By comparison, kea survival estimates for previous studies in western South Island areas were mostly above 90 per cent.
The sharp increase in predation of the study of kea coincided with the crash of mouse populations in eastern valleys the year after the beech mast.
Kemp said this may have contributed to stoats taking larger prey, like kea, but further work was required to confirm whether this was the case.
The exact cause of the increase in cat predation was unknown, although there had been reports of feral cat numbers rising in the study area over the past five years.
Most of the kea tracked in the study lived in areas where predators weren't currently controlled.
However, two birds were killed by either stoats or feral cats in the Hawdon valley in Arthur's Pass National Park where predator control targets rats and stoats to protect orange-fronted parakeet and other native species.
The new findings come as DOC has warned of another potential mast seeding event next summer.
Scientists have suggested these plague-making events may be increasing with climate change – something that was also threatening kea and other vulnerable alpine species by bringing pest predators to higher reaches.
Meanwhile, another study, published today, has revealed how each stoat appears to have a second-favourite food in New Zealand.
While stoats preferred to prey on rats, the new DoC-led research showed that when there aren't enough of them to eat, individual stoats would focus on a small number of other prey.
But, as a whole, the stoat population was still managing to kill a large variety of prey.
The study author suggested this knowledge could change how we approach trapping, or help identify periods when native species are most at risk.
