The population of mohua, one of New Zealand's rarest songbirds, in the Catlins was increasing after a successful joint agency pest control programme last spring, DOC said.
DOC's focus was to control rats and stoats to protect mohua in 10,000ha of beech forest, while TBfree New Zealand targeted possums to control bovine tuberculosis (TB) over 37,000ha surrounding this area.
Mohua number less than 5000 and are found only in small isolated populations in the South Island and several small islands near Stewart Island, such as Ulva Island and Codfish Island, and Resolution Island in Fiordland.
DOC conservation services manager David Agnew said monitoring results showed mohua numbers increased to the highest level recorded since the population suffered a big decline about 14 years ago.
"Surveys show the population is recovering well after the pest control in August," Mr Agnew said.
"We found more birds and they have expanded into areas they used to be found in."
The opportunity to piggy-back on the TBfree operation when rat levels were increasing meant the mohua could be protected at the start of their nesting season in October when they were most vulnerable, he said.
The coordinated operation considerably decreased possum numbers, the main source of TB in livestock, and helped maintain the progress already made in reducing the risk of TB-infected wild animals spreading the disease to farmed cattle and deer in the surrounding area.
Rat levels, which were tracking at between 14 and 18 per cent in mid to low-altitude forest areas in August, fell to undetectable levels after the 1080 operation. Possum numbers also fell.
The Catlins mohua population, estimated to be several thousand, is one of the largest remaining in the South Island.
Survey results for 2013 show an increase in the average number of mohua and groups of birds from 2012 and previous highs in 2004 and 2008. Record numbers of bellbird and tomtit were also observed, Mr Agnew said.
DOC last used aerial 1080 to target rats and stoats in the Catlins after a big beech mast or seeding event in 2009.
A large beech mast is predicted to result in a pest plague this autumn and rodent levels in the Catlins will be monitored closely to determine whether a pest control response is needed later this year as part of DOC's Battle for our Birds programme.
First published in the The Southland Times