One of New Zealand's longest-standing conservation sponsorships will come to an end this month.

Following 25 years helping to save New Zealand's iconic Kakapo from extinction, New Zealand's Aluminium Smelter (NZAS) has made the difficult decision to step down as major sponsor of the Kakapo Recovery Programme at the end of 2015.

"We are sad to be stepping down, however we are very proud to have played our part in helping to save this critically endangered species. There were only 49 Kakapo when we first started, now there are 125," NZAS chief executive and general manager Gretta Stephens said.

"We initially signalled to our partners in 2003 that market conditions and a changing external environment meant our continued sponsorship was unlikely. However, we managed to continue underpinning efforts to save this iconic New Zealand bird for another 12 years. We notified DOC in August 2012 of our intention to exit at the end of this contract and unfortunately the current commercial situation has forced us to finally withdraw."

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Commercial conditions continue to be very difficult for NZAS with issues around electricity and transmission prices and a very low aluminium price. In 1990 the aluminium price was NZ$4545 per tonne. Today that price has halved to NZ$2250 per tonne, Stephens said.

DOC director-general Lou Sanson said DOC sincerely thanked NZAS for its long-standing support of the Kakapo Recovery Programme.

"With NZAS' support over the last 25 years Kākāpō Recovery has become a highly successful programme recognised around the world," he said.

Kakapo Recovery work would not be affected by NZAS's decision and DOC has made good progress on securing another long-term partner in this programme, Sanson said.

NZAS began funding the Kākāpō Recovery programme in 1990 and has contributed $4.5 million and more than 1100 employee volunteer days during that time.

Stephens said she was very proud of the support offered by smelter employees, with many of them expressing that their time spent on the islands during the years has been life-changing.

Employees had carried out maintenance to island infrastructure, as well as assisting with kakapo supplementary feeding and nest minding, she said.

"NZAS' contribution has provided 25 years of certainty for Kakapo Recovery and helped to make it into the world-leading conservation programme it is today. I urge other New Zealand organisations to now take up the challenge," Stephens said.

Last month, Air New Zealand refused to rule out stepping in to the sponsorship role, but a company spokeswoman said no decisions had been made.

Air New Zealand recently announced an extension of their partnership with DOC, which is worth $1 million annually, through until 2020.

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