T7787 is just 10.5 grams. Photo: Supplied / Jennifer Gollin
A bat of at least 26 years is officially New Zealand's oldest known long-tailed bat/pekapeka.
Known as T7787, she was caught as part of a bat monitoring programme in Fiordland this month.
She was given a quick health check, then released to rejoin her colony at Walker Creek in the Eglinton Valley, where she has lived her entire life.
She weighs just 10.5 grams, about the same as a AAA battery.
Department of Conservation principal scientist Colin O'Donnell, who leads the bat monitoring work, said that T7787 was first caught in 2000 when she was a young mother, and again this month.
DOC principal scientist Colin O'Donnell holds T7787. Photo: Supplied / Keith Barber
As female bats are able to breed from two years old, O'Donnell said she was at least 26, but possibly as old as 28.
"She's going a little grey but still appears in good health," he said.
O'Donnell said the signs of her age included that she has stopped breeding, but had produced a pup every year for 20 years.
Most of the 1400 bat species around the world live between six and 20 years on average, although a small number are known to live more than 30 years.
"We don't know how long our bats live for so it's exciting to get this record," he said.
Long-tailed bats were threatened with extinction, having declined dramatically since pre-human times because of habitat loss and predation by introduced pests.
However, long-term monitoring of both long-tailed and short-tailed bats by DOC has shown a steady increase in bat numbers in response to large-scale predator control using trapping, bait stations and aerial 1080 to target rats, stoats and possums.
Prior to 2000, the long-tailed bat population was declining by 5 percent every year but that has been reversed and is now growing by 5 percent.
Before T7787, the previous oldest long-tailed bat, recorded and last seen in 2015, was another female, A78806, who was 25.