Kea Conservation Trust chairwoman Tamsin Orr-Walker described the deaths as "devastating" given there were fewer than 7000 of the nationally endangered species left.
At the time, DOC staff blamed tourists feeding the kea for the birds' willingness to take the 1080 bait.
Emails and text messages released to Stuff, under the Official Information Act reveal one DOC staff member believed the birds' scrounging and the two pre-feeds that preceded the drop had created a "perfect storm". The pre-feeds involve using non-toxic bait to attract the target species – predators such as rats and stoats in this case – and encourage them to take the poisoned bait later.
It was "pretty predictable" the kea deaths would occur, the staffer wrote. Another wrote that in a location like Matukituki "we expect some kea deaths to occur," due to the level of scrounging.
The two pre-feeds were given eight weeks apart, due to heavy rain after the first in late November.
This was in line with DOC's Kea Code of Practice, but the first staff member wrote that DOC should not be pre-feeding twice in "red zones" such as the Matukituki Valley – areas where kea exhibit scrounging behaviour.
Another staffer also appeared to have concerns, noting that they had missed this information when the draft Code of Practice was written
"I’d like to think I would have raised a red flag about it.”
In an interview with Stuff DOC's biodiversity threats unit Nelson manager, Meg Rutledge, said there were differing opinions within the department on the effect of pre-feeds on kea behaviour.
The deaths of the six kea were not predictable and were regrettable, she said.
"However, the science on the risks and benefits of predator control to kea gave us confidence that the effective control of rats and stoats would benefit the kea population as well as other native species in these valleys."
The documents show DOC director-general Lou Sanson asked why research into kea had been "deprioritised".
Deputy director-general Martin Kessick responded that kea research remained a priority and outlined seven ongoing projects including monitoring kea survival through 1080 operations.
However, a separate email from Rutledge confirmed kea were not monitored in the Matukituki operation.
"At the moment, DOC operations teams are not budgeted to include species monitoring associated with every aerial 1080 operation. DOC teams would welcome the opportunity to undertake this work if resources were available," she wrote.
Monitoring was under way in the Hawdon Valley in Arthur's Pass, and would be undertaken alongside an operation in Wet Jacket Arm, Fiordland later this year.
Rutledge also confirmed no specific review of the area was held before the 1080 drop on Matukituki, as was planned for future drops in Okarito and Otira on the West Coast.
Orr-Walker said there had been a definite change in the way DOC approached research and monitoring of kea in recent years.
"I am really aware after these results that we need to actually step up and start really looking at methods for mitigating kea deaths during 1080 operations."
The trust supported the use of broad-scale landscape pest control though, she said.
"We've got thousands of hours of footage showing kea nests being predated on by rats, stoats, possums and feral cats."
Rutledge said DOC had since budgeted up to $150,000 over three years for research on changing human behaviour to prevent kea scrounging.
The documents reveal at least nine DOC staffers were involved over two weeks preparing a communication's strategy before releasing information to the public about the kea deaths.
Dozens of emails were sent discussing the strategy between February 17, after it first became clear there were likely deaths, and March 2, when the information was made public.
The plan was to wait for autopsy results before releasing any information, but by February 24 there was pressure from Ngāi Tahu to advise all southern rūnanga.
Emails show DOC staff feared that would lead to the information becoming public.
"Some members of Ngāi Tahu are not supportive of 1080," DOC South Island operations manager Aaron Fleming wrote.
Rutledge said one reason for the delays was the amount of time it took to retrieve the birds and for the autopsies to be completed.
"We were waiting for actual clear outcomes rather than speculation."