"Long-tailed bats face predation from rats, stoats, possums and cats because they choose to nest in the cavities of older trees up to 17 metres off the ground," Carr said.
The bats are nocturnal and make homes in large trees such as totara, puriri and kauri.
Tāika Forest provided a favourable habitat for the bats, Carr said, and the NRC planned to increase pest control in the forest after the discovery.
She encouraged anyone who thinks they have spotted the endangered mammals to call the NRC on 0800 002 004.
"The best time to spot the bats is on dusk. They can easily be mistaken for a Welcome swallow so people have to look closely," Carr said.
"Many properties on the city fringe with native bush or pines on-site may just be providing a habitat for these furry friends without realising."
The NRC's report on the forest also found a new species of mayfly and the peripatus or velvet worm.