A colony of endangered South Island long-tailed bats has been discovered on D'Urville Island in the Marlborough Sounds.
The bat colony was found by a Forest and Bird team during a survey on the island in January.
The long-tailed bat population on the island is estimated to number in the hundreds.
"This find is fantastic news," Forest and Bird spokeswoman Debs Martin says.
"It means that D'Urville Island is even more important to New Zealand's natural heritage than we thought."
Just 10 colonies of long-tailed bats are known to remain on the South Island mainland, with total numbers fewer than 5000, and declining.
"D'Urville Island is the fifth largest island in New Zealand. One third of it is public conservation land. It is free of possums and ship rats, which increases the long-tailed bat's chances of survival," Ms Martin said.
"This find dramatically increases the chances of saving the species from extinction," she said.
"It was predicted that the South Island long-tailed bat would become extinct within 50 years. But this find may well alter that."
Forest and Bird will now be working with the Department of Conservation, local iwi and landowners to monitor the bats.