Short-tailed bats had not been seen or heard in the Tararua Forest Park for more than 50 years before a small population was rediscovered in 1999, in the Waiohine Valley on the Wairarapa side of the ranges.
Believed to be the last remaining population of short-tailed bats in the south of the North Island, it was isolated from other bat populations about 90,000 years ago by volcanic activity, and glaciation.
They are thought to be related to both the volcanic plateau and the southern short-tailed bats.
The population of around 300 bats is now believed to be under siege from predators.
Ambitious bat rescue plan
To improve the security of the bats, by establishing a population in another place, DOC attempted the most ambitious conservation project ever involving bats New Zealand.
During 2005 and 2006, pregnant bats were taken from the Waiohine Valley to the National Wildlife Centre at Pukaha Mount Bruce until they had given birth and weaned their pups.
The mothers were then returned to the wild. Their 25 pups were taken to Kapiti Island and kept in captivity for another couple of months before being released into the wild.
The plan worked and the bats stayed on the island, the first successful translocation of a population of bats internationally. While 12 survived their first year - greater survival than would have been expected for their Waiohine counterparts - they developed a dermatitis infection on their ears which was unable to be treated in the wild.
If left to their own devices, it is likely they would have died as they could no longer properly echo-locate (a bat's sonar system for navigating and catching prey). They were recaptured and taken to Auckland Zoo and the translocation was put on hold.
Protecting the roosts
DOC is now focusing on protecting the bats in the wild, by trapping rats and stoats in the area surrounding the communal roosts during the summer period when they are rearing young. Rat and stoat numbers have reduced by more than 80% each summer since December 2008, when this work began.
To determine the success of the pest control, the communal roosts are being monitored by video. The numbers of bats using the roosts are being counted, and their echo-location calls recorded to find out how active they are.
It will take several years to demonstrate that pest control has improved bat breeding survival because breeding females have just one pup each a year.
Translocating juveniles to a safe location may also be attempted in the future
Increasing support for the work is a key part of the project, which is managed by DOC with support from Kahungunu ki Wairarapa. BDG Synthesis, a bio-analytical chemist company with a conservation sponsorship programme, has paid for electronic equipment.
Community involvement is slowly developing, with volunteers interested in both field work and data handling and development.
Waiohine bat facts
The Waiohine bats were rediscovered by distributing small waterproof containers that automatically record conversing bats.
For three months, rain, wind were the only sounds recorded. Then, at the 11th hour, a noise like “a ball bearing being dropped onto a slab of marble” was heard. It was the distinctive 'voice' of the short-tailed bat.
Their habitat is typical of eastern Tararua foothills: beech and kamahi forest with rimu and rata in the lower valley, 200 to 800 m above sea level with rainfall about 3000 mm per year.
The range of the bats extends from the Waiohine roadend in the south to Totara Flats and Totara Creek to the north.
Bat pups are born around Christmas Day, and raised in a communal roost called a maternity roost. Pups are born large - about a third of their mother’s weight - and over six weeks they are fed by their mums in this big nursery until they reach adult size and are ready to fly and leave the roost in February.
How to find a quiet, fast flying nocturnal bat
The best tool for locating bats is a bat recorder - a tape recorder that can pick the ultrasonic sounds that bats use to navigate in the dark.
Bats are caught by putting up mist nets in the places they fly past. By attaching small transmitters on their backs, they can be tracked back to their communal roosts using radio telemetry.
At their communal roosts a harp trap, which looks like a harp, is used to catch bats safely and easily to assess their gender and condition and, for females, whether they are breeding.
Because of their silent flight, these small bats are very difficult to see or hear, even when you are very close. Because of this very few people ever see them.