Rob Suisted

Bat signals

Nightfall, and the forest comes alive with squeaking. Or it used to. Lesser short-tailed bats are clinging on in a handful of places, their populations blinking out of existence. Yet researchers are only just beginning to learn about our bat species—New Zealand’s only native mammals—and what they’re finding out is pretty weird.

Written by       Photographed by Rob Suisted

Bags of bats await scanning and radio-tagging. Data-loggers placed on roost trees collect three weeks’ worth of information for DOC to analyse. It’s enough to measure bat survival rates, says Abi Quinnell: How many of the bats recorded last year are present this year? The survey allows DOC to keep a watchful eye over this small population, ensuring pest control is functioning well and any sudden decline in numbers is spotted.
Bats cling to the catch bag below the harp trap. This population in Pureora Forest Park is thought to be stable, and overall, the lesser short-tailed bat isn’t doing too badly; in 2018, the species was reclassified from ‘threatened’ to ‘at risk and recovering’, an improvement in their status. By contrast, New Zealand’s other bat species, the long-tailed bat, is ranked ‘nationally critical’.

“Can you hear that?”

asks Abi Quinnell, gazing up at the tōtara, its branches reaching into the darkening sky. The tree is showing its age, its bark flaking away in long strips. I listen, but all I can hear is Pureora Forest Park’s dusk choir—the squawking of kākā, the twittering of North Island robins, the haunting calls of ruru.

I strain my ears, and begin to make out a chattering sound—faint but high-pitched, as though a collection of squeaky toys has come to life.

“Is that them?” I whisper.

Without taking her eyes off the tree, Quinnell whispers back: “Yep. That’s them.”

Quinnell, a biodiversity ranger for the Department of Conservation (DOC), switches on an electronic bat detector. It crackles to life and, like a megaphone, begins to amplify the bats’ calls, converting their ultrasound echolocation signals into sounds we can hear. They are frantic, shrill. If a satellite was one day to intercept communication from outer space, I imagine it would sound something like this.

This roost of lesser short-tailed bats, pekapeka-tou-poto, is just waking up. Soon, they’ll fly out into the forest to feed—straight into the trap Quinnell and her team have set for them. Tonight, they’re aiming to radio-tag 60 to 70 bats from this roost in a surveillance mission that acts as a rough census. Once the bats are tagged, dataloggers attached to roost trees such as this tōtara will record their comings and goings. How many bats who were recorded last year are still alive this year? Has the population changed—or is it stable?

Once harp traps are raised into trees where lesser short-tailed bats roost, Department of Conservation staff wait for night to fall. Short-tailed bats leave the roost to hunt for nectar, pollen, fruit and insects. This research takes place every summer: in colder weather, bats enter a state called ‘torpor’ and stay home until it’s warm again.

It doesn’t take much to send a bat population into decline. In 2010, a male tabby cat killed 102 lesser short-tailed bats in a week before a DOC ranger apprehended it. The cat had found a roost located within a giant beech tree, nicknamed ‘The Mothership’, on the southern slope of Mount Ruapehu, and was feasting there, leaving individual bat wings scattered on the forest floor. In 2017, an entire population of short-tailed bats vanished from Tararua Forest Park.

The lesser short-tailed bat’s cousin, the greater short-tailed bat, was last seen in 1967—an invasion of ship rats probably wiped it out. (Recently, a few unconfirmed sounds in the night mean this species has been reclassified by DOC as ‘data deficient’, or ‘might be alive, but we don’t know’.)

Pureora is home to about 1000 bats. So far, the population is stable, with an adult female survival rate of more than 80 per cent—but Quinnell points out that a bad storm, a swell in predator numbers, a new disease or a rogue cat is all it would take to send them into decline.

“There’s nothing to indicate that we need to panic,” she says. “But it doesn’t mean that we can relax.

“I don’t want to be in the position where we think it’s all good and there are plenty of bats, and then suddenly there are not many bats, and then there are hardly any bats, and then there are no bats.”

[Chapter Break]

Short-tailed bats remain a mystery. The effort to protect and learn about them got under way only in the late 1990s, when DOC rangers discovered a few hundred short-tailed bats in Fiordland’s Eglinton Valley. More than 20 years later, that population has grown to about 3000 bats, largely thanks to intensive pest control, which has expanded from 50 to 3500 hectares.

Success in the Eglinton Valley was the catalyst for research in Pureora, which began in 2011. The Pureora population is unique in a way that makes it much easier to study: bats return to the same roosts over and over again. This is probably because it’s a small population in a small area, says Quinnell: “We don’t know if they especially like these trees, or if there’s just nothing else that suits.”

Lesser short-tailed bats are renowned for their propensity to bite, especially compared to long-tailed bats, a more docile species.

Most short-tailed bats are constantly on the move, meaning that DOC rangers have to find their new roosts. Bat-monitoring missions in places such as Ohakune begin with a search: rangers circle forested areas in a small plane, listening with bat detectors, then tramp in to catch bats in mist nests, attach radio transmitters, and finally, track them back to their roosts.

Pureora bats lead more routine lives: Quinnell simply follows their poo. She lays tarpaulins under known roosting trees and returns the next day to see if the tarps are covered in guano.

This tōtara tested positive for bats in residence, so the team fixed ropes in its upper branches and hoisted a harp trap to cover the main entrance to the roost. Harp traps have two parallel webs of fishing line, the second slightly offset. Bats veer through the first web but crash into the second and fall into a catch bag below.

All we have to do is wait. That’s the idea, anyway. It’s possible that there are other exits in the tree that would allow the bats to escape if they suspect something’s up. I don’t want to be the one to tip them off, so I shut up, squat on a rotten log, and listen.


It begins with the gentle thud of a bat falling into the catch bag. Then another—like light rain on a roof. The bag fills up with bats flapping their wings and scrambling up into the plastic sleeve. We lower it to the ground, and here they are: about 80 of them huddled together, lit up by head torches.

The first thing that strikes me about them is their size—tiny, like mice, with fine, velvet-like, grey-brown fur. They have oversized ears, shaped like bay leaves, and black pinheads for eyes. Their pug-like noses protrude from their faces like swollen glands. For an animal that feeds mostly on insects, pollen and nectar, the giant fangs seem like overkill to me: four sharp incisors. No wonder people associate them with vampires.

Their wings—those dark, translucent membranes—can fold up like origami, but they’re an impressive sight when fully outstretched: about 30 centimetres from tip to tip.

“You fold out their wing and you can see the shoulder back to the elbow within the wing membrane, the forearm and the thumb pointing forward and the long finger bones and you’re like, ‘It’s a hand, it’s a human hand, it’s just a different shape’,” says Quinnell.

It’s only then that I truly understand that this tiny, peculiar, rather ugly creature is a mammal, like us. And, at the same time, nothing like us.

Someone jokes that to the bats, this must seem like an alien abduction—bright lights, foreign beings, strange sounds, being carried off in an unfamiliar floating object to undergo an invasive surgical procedure: “No one’s going to believe them when they get back to the roost.”

[Chapter Break]

Bats are a “very weird group of animals”, says ecologist Cory Toth, who completed his PhD on the Pureora population. He adds that, of more than 1200 species around the world, New Zealand’s short-tailed bat is “one of the weirdest and most unique”.

That’s because it evolved here, with few land-based predators, adapting to forage mostly on the forest floor. The short-tailed bat can tightly fold its wings to create two forelegs that it uses to scurry along the ground, hunting for insects. It’s one of the only terrestrial bats in the world, and this makes it vulnerable to rats, stoats and possums.

It also has a peculiar sex life. Toth’s research found that short-tailed bats are one of only two bat species internationally to use a lek mating system—where males compete for the attention of females in elaborate displays.

This lesser short-tailed bat, or pekapeka-tou-poto, is flying on its side, looking down—photographer Rob Suisted is positioned below it. Each bat took a different flight path upon release following radio-tagging, says Suisted: there was no predicting which direction they’d go in.

New Zealand’s most famous lek breeders are kākāpō. During the breeding season, male kākāpō construct bowls in the earth, where they make booming sounds by night. It’s a question of the best bowl, the most bewitching boom. Male bats, by contrast, attract mates by singing while peeing on themselves. The scent, apparently, allows female bats to figure out which bats are their brothers or cousins.

Male bats’ songs can be heard throughout the night at Pureora and are about as tuneful as a squeaky wheel on a supermarket trolley. They station themselves in singing roosts, soundstages close to the maternity roosts from which females come and go, feeding their pups.

Toth found that smaller males sing more, and so are more popular with the ladies. Larger males bolster their chances by making a kind of timeshare arrangement, where up to five bats use the same singing roost during a night, one at a time. Toth reckons that taking turns means there’s always a song being broadcast from the roost, making it a more appealing destination. (Think of it as a boy band versus a solo artist.) During their serenades, males spray urine over themselves near-constantly. Toth thinks this may be a way to maintain genetic diversity in small population groups.

“We know in other species urine contains information on relatedness,” he says. “That could be a way for females to avoid mating with close relatives.”

[Chapter Break]

Wearing thick gloves, Abi Quinnell and senior ranger Tertia Thurley sort the bats into cotton bags, like small pillowcases closed with drawstrings, five to a bag. Bats already wearing radio tags are released into the night. We carry the bags to our makeshift field hospital—a couple of tarpaulin shelters and a few fold-out camping chairs in the middle of the forest—and peg them onto a clothesline.

This is familiar work for Thurley, who managed the bat programme here for eight years. She’s back from her new post in Northland to lend a hand during Quinnell’s first year running it.

You can hear the bats squeaking and shuffling in the bags. You can smell them, too—an earthy, sweet odour, like damp cannabis. Quinnell and Thurley take their places on the chairs, alongside biodiversity ranger Sarah Wills and technical advisor Jess Scrimgeour.

This species’ stumpy tail, top, is one of the features distinguishing short-tailed bats from long-tailed bats. Researchers examine the bats’ finger joints in order to determine age: juveniles’ joints aren’t fully formed, so torchlight passes through.

“Can someone pass me a bag of bats,” asks Thurley, the way one might order fish and chips. “One bag of bats coming right up,” says biodiversity ranger Tim Quinnell, Abi’s husband. Thurley removes a bat from its bag and scans it, like a supermarket item, to double-check it hasn’t already been radio-tagged. It hasn’t, so she lays it out on her lap and holds it still between her index fingers and thumbs. The bat squirms and squeaks in protest.

“It takes getting used to, because they can and do bite, and can be really wriggly,” she says. “But once you get a handle on just going with their movements a little bit—what you can and can’t do—it gets easier.”

The bat’s sex is recorded, plus its age—adult or juvenile. This one’s a female, so Thurley also checks its nipples to see whether it has been lactating: swelling, or a bare patch around the nipple are both clues. (Short-tailed bats give birth to only one pup per breeding season.) Then Wills lines up a steel gun fitted with a large, sterile needle. The whole thing is about twice the size of the bat. She massages the animal’s back to loosen the thin layer of skin, then, with a steady hand—any movement or misfire could cause injury—slides the needle containing the tag in between the shoulder blades. The tag is released, needle removed, and wound sealed with a dab of Superglue. The surgery is over in seconds. The bat is released into the darkness, collecting data on its travels that might one day contribute to the future of its species.

[Chapter Break]

Right now, that future is murky. While endangered birds can usually be protected by transferring them to predator-free sanctuaries, this doesn’t seem to be the case for bats, which don’t stay where you put them. In 1994, 100 short-tailed bats, some fitted with radio tags, were translocated from Whenua Hou/Codfish Island to Ulva Island on the other side of Rakiura/Stewart Island, but the bats left Ulva almost immediately and disappeared. It’s possible that they flew home to Whenua Hou, but their fate remains a mystery. Another attempt to establish a colony of short-tailed bats on predator-free Kāpiti Island in 2005 failed when the bats developed an ear infection.

As well as losing bat populations, we also find them again. Earlier this year, short-tailed bats were discovered in the Ettrick Burn area of the Murchison Mountains, and work is under way to locate roosts and estimate numbers. A small population was also confirmed in Northland last November, in Puketi and Omahuta forests, but it’s believed to be in danger of an imminent collapse.

Colin O’Donnell, DOC principal science advisor and leader of its Bat Recovery Group, remains optimistic.

The lesser short-tailed bat is tiny—five to six centimetres from head to tail. Each bat weighs 12 to 15 grams, about as much as a heaped tablespoon of sugar. They’re unusually long-lived for such a small animal: a bat tagged in the Eglinton Valley is at least 23 years old. Mice, which are about the same size, live for about a year.

“There’s no reason to think we can’t turn the decline over fairly big chunks of New Zealand,” he says. “We’ve identified the causes of decline and found some solutions to managing them.

“It’s exciting to see the turnaround in numbers of the couple of populations we have left. It will be dependent on us keeping up our conservation efforts, of course, because, unfortunately, they won’t be able to look after themselves.”

Sometimes, with bats, it’s a question of who’s listening, and where. Quinnell used to monitor long-tailed bats as a teenager, on tramping trips near Hokitika with her father, using an old-fashioned bat detector, a dictaphone, and a talking clock, all sealed in a two-litre ice cream container. (The bat detector broadcast the calls, the clock provided a time stamp by reading out the hour, and the dictaphone recorded it all.) Sometimes, it recorded squeaking. Such a rudimentary system couldn’t tell you if it was one bat or many passing by, says Quinnell, but it was a sign that the bats were out there, somewhere, leading their mysterious lives.

[Chapter Break]

After three nights of tagging, the Pureora operation draws to a close. It’s the early hours of Thursday morning. The tarpaulins are folded, traps disassembled, camping chairs dismantled. There’s little conversation as we walk through the forest and return to base, the old Pureora fire station, where staff and volunteers catch up on sleep in tents, caravans, and a small bunkroom. It’s work like this happening all over the country that’s giving the short-tailed bat a chance.

“We can’t lose these remnant populations,” says Quinnell. “They’re really rare and may well be disappearing. With every species, you don’t know how essential it is.”

Tertia Thurley’s purpose here is simple. Yes, she says, it’s about preserving the ecological value that the bats bring to the forest—what some scientists call ecosystem services, the bats’ roles as pollinators, predators and prey.

“But it’s not just for their services,” she says. “It’s for the bats.”

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