Michael Schneider

The remarkable world of bats

I have in my hand a small, warm bat. Wings folded, she fits perfectly in my palm, and her chestnut fur, damp from the evening dew, is spiky in a punkish sort of way. She is groggy with sleep; she has been napping-something bats do wonderfully well-whie she awaited rescue from the benign trap set for her, this most unusual little mammal.

Written by       Photographed by Michael Schneider

We’ve been trying for four nights to catch this bat among the giant rimu and kahikatea of an ancient piece of New Zealand forest at Puketitiri, near Napier. Our group includes Nick Gillingham and Tony McCann, two of a dozen scientists who are trying to unreavel the mysterious world of New Zealand’s tow species of native bat.

We know only the sketchiest of details about the bat we have caught-the long-tailed species-and its ancient, and scientifically even more precious, cousin, the short-tailed bat. They are the only terrestrial mammals which were present in New Zealand before humans. Long before humans. A million years ago, the ancestors of our long-tails probably blew in from Australia. Short-tails were already ancient residents. Recent DNA studies suggest that they diverged from South American bat stock some 35 million years ago; but New Zealand was last physically joined to that part of the world 65 million years ago, so just how and when they arrived here remains a mystery.

Nick and Tony are both quiet and rather dreamy people, possibly be­cause to do this work they have to live a life close to that of the bats: awake through the night, asleep for much of the day. By night, they go into the forest armed with the bat researcher’s tools of trade: harp-like traps with fine strings which the bats fly against, then slide gently down into holding bags; nets as fine as mist which the bats cannot sense and which hold them tenderly like cobwebs until the scientists pick them out; bat detectors with high-frequency microphones to pick up the bats’ calls. To our ears, bats in flight are perfectly silent, but in fact they make a lot of noise. We could have hundreds of them flying over us in the darkness, but without de­tectors we would never know that.

Each night during summer, Tony and Nick set the traps across streams, the insect-rich super­highways of the bats, and when they catch a female bat they check her for signs of pregnancy, then glue a tiny transmitter on her back and let her go. The transmitter emits a steady stream of electronic beeps, and late the following afternoon, while the bat sleeps, they set out with their receiver to track her, filling in an­other fragment of our scant know­ledge about where bats live, how far they fly and how they conduct their lives. And here is the scientists’ nightmare: each night these bats

move to a new roost, another hole high up in one of these huge trees—returning seldom, it seems, to a former roost. Sometimes they’ll move as far as 15 kilometres away. So each day the scientists’ search starts, yet again, blind.

As Nick carefully stretches our captive bat’s wing to measure it, I trace the fragile bones of the shape that has become a comic-book icon. All bats belong to the order Chiroptera, literally “hand wing,” and the long delicate fingers, even a small thumb at the top of each wing, are clear to see through the almost translucent membrane. Cool to the touch, the membrane is rubbery and feels like cling wrap. With her wings out she is about the same size as a swallow; wings folded, she is the size of a mouse and weighs only 12 grams, lighter than Nick would ex­pect her to be if she were pregnant.

She has no milk, either, which means that, unlike most of the fe­males Nick and Tony have caught recently, she has not given birth this summer. Maybe she’s still too young; maybe she’s too old. And too old in this case could be astonish­ingly old, up to around 35 years. For their size, these are the longest-lived mammals on earth.

Now in my hand I feel the bat’s small body vibrating, and she yawns, displaying a neat row of sharp little teeth. “She’s revving up,” Nick warns. Soon she will come out of this sleepy state and will fly away. All measurements are complete, and the transmitter glued in place between her shoulder blades. Cameras are set up to record the flight. For future reference, in­stead of a number we give her a name. Emily. Our bat detector starts slowly tock-tocking. She has begun echolocating—sending out sonar clicks, the return echoes of which enable her to “see” in her dark world. Now, pulling herself along, wing over wing, she scrambles to my fingertips and launches herself. For one sliver of an instant she flies towards the camera; then the flash freezes her in the middle of the tight­est and most graceful roll any pilot will ever make. As she accelerates away from us, her wings flicker in our torch beams like a strobe light.

Now only the mocking tock of the detector tells us that she is sweeping overhead and away. The fragile and dopey little handful has suddenly become a masterful creature of the night.

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Bats fall into two groups the “mega” bats and the “micro” bats—and they’re as different from each other as dogs are from cats. There is even debate among bat people about whether they came from a common ancestor. Some sci­entists suggest that the mega-bats, the large flying foxes and fruit-eat­ing species, may be distantly related to humans.

These big bats have large eyes, see well in available light, and don’t rely on ultrasonic echolocation. The micro-bats also have good eyesight, but rely at night on their echoloca­tion to build up a picture of their surroundings.

Humans have a very narrow hear­ing range. At our youngest and best, before we expose our hearing to loud rock bands, pneumatic drills and constant traffic din, our hearing runs out at 20 kilohertz. That’s where a lot of mammals—and in­sects—start. Short-tailed bats emit their ultrasonic calls over a wide range of frequencies, some higher than 100 kHz. They are most easily detected at about 27 kHz, and long-tailed bats at about 40 kHz.

“Think of echolocation as a sort of vocal Braille,” Tony says. “They shout, the echo comes back, and they can piece clues together from that information. If the echoes start coming faster or louder, they know the insect they are stalking is closer.” When they’re closing in on a quarry, the rapid regular calls turn into a blur—if they couldn’t send and receive calls quickly they would be temporarily “blinded.”

Bats which fly in open spaces above the trees need loud long-dis­tance calls—there are few obstacles in their way, and they have to “spot” their prey at a distance. Others, which live in dense jungle, need only whisper. New Zealand bats, which live in a a complex bush en­vironment, only want to know what’s happening in front of their noses, so they have weak rapid calls.

Of the 4200 living species of mammals, almost a thousand of them are bats. Only rodents, with 1700, have more species. The oldest known bat fossils, found in slate de­posits in Germany, date back to early Eocene times, between 56 and 65 million years ago. And even then, according to the research, they were perfectly recognisable bats. The en­suing millennia have given them ample time to evolve into some of the most peculiar and specialised animals on our planet.

There are bats for all occasions: one has flashy white tufts under its wings, with which it impresses and seduces its mates; a bat in Mexico has specially enlarged toes so it can drag them through the water and gaff fish. There are frog-eating bats, even bat-eating bats. And there are the maligned and furtive blood-lap­ping vampire bats of South America (see page 102).

The Egyptian bat gives birth to offspring with human-looking faces; another species has echolocation equipment which looks like a satel­lite dish stuck on its nose. Bats in the family Rhinolophidae have so much nasal foliage they can’t see over it. Still others come with spikes and spears on their faces with which they can direct sounds. The combi­nation, says naturalist David Attenborough, “is often more gro­tesque than any painted devil in a medieval manuscript.”

The largest carnivorous bat, Vampyrum spectrum of Costa Rica, has a wingspan of over a metre and stalks the jungle at night hunting for birds and rats. The smallest bat, with a wingspan the length of a match­stick, is the bumblebee bat of Thai­land. In the last 20 years the forest in which this bat lives has been heav­ily culled, and it may be that the bat has not survived. If it has, it is prob­ably the smallest mammal alive.

Both New Zealand bats are micro-bats. Our long-tailed species, Chalinolobus tuberculatus, is closely related to other species in the western Pacific, but the short-tailed bat, Mystacina tuberculata, is so different from other bats that it has a taxonomic family all to itself.

When not in use, the short-tail’s wings are furled against its forearms like an umbrella and covered by the tough leading edge of the wing. This means that the delicate membrane is well tucked away when the bat wants to do what it is uniquely good at: scrabbling around among the leaf litter looking for grubs. This unu­sual behaviour (for bats) mirrors a past in which bats—like our many flightless birds—could roam the for­est floor untrou­bled by any foes. Sadly, this world has long since dis­appeared.

The first person to record seeing a bat in New Zea­land was Johann Forster, a naturalist with Captain Cook. While surveying Queen Charlotte Sound on Cook’s 1772 to 1774 jour­ney, he saw a bat flying over the sea­shore, and in the swashbuckling way that early naturalists seemed to share, he shot it. It lived long enough for his son to make a drawing of it, and was named Vespertilio tuberculata, a name later changed to Mystacina when scientists realised the creature’s uniqueness.

Forster’s treatment of the bat fore­shadowed what lay ahead: history records naturalists burning trees to flush out the bats, swatting them one by one as they emerged so they could tally the numbers. A report from the Napier area tells of sleepy bats tumbling out of giant forest trees as they fell, and “as like as not the loggers would go around stamp­ing on them.”

Although we have not, as some countries have, knowingly set out to exterminate them, through the intro­duction of predators and the mind­less destruction of their homes in mature native forests we have made their survival precarious.

The long-tailed bat is the more common of the two. It seems to be still widely distributed in pockets throughout New Zealand, and South Island researcher Colin O’Donnell has found over 150 roosts in a single valley in Fiordland. Populations of the short-tailed bat are much more scattered: Codfish Island, near Stewart Island, nothing definite in the South Island, occasional populations across the central North Island between Taranaki, National Park and Waikaremoana, Little Bar­rier Island, Omahuta and Warawara forests in Northland.

There used to be a third native bat, a sturdier version of the short-tailed bat called Mystacina robusta. Hunted to near extinction by laugh­ing owls on the mainland, its last retreat was an island to the south of Stewart Island called Big South Cape. It was a glorious place, so glo­rious that two of the country’s early naturalists, Edgar Stead and William Guthrie-Smith, who visited and wrote about the island, would not divulge its name for fear that others would go there and damage it.

Big South Cape was a genuine fragment of prehuman New Zea­land, where by day bush wrens, rob­ins and saddlebacks would fill the bush, and at night weta, beetles and bats would claim their domain. Then, in the early 1960s, ship rats arrived—probably escapees from fishing boats. By 1965, the rats had decimated the island’s wildlife. Half the bird species had gone, and with them the last Mystacina robusta.

One day, while I was visiting the Wellington home of Mike Daniel, who has worked with bats for more than a decade, he suddenly handed me a bottle. In it a chunky little bat with sturdy legs floated in alcohol.

“This is the robusta,” he said.

As I looked at the sorry mass of fur and bone I realised I was holding perhaps the last greater short-tailed bat in the world—a fragment of New Zealand’s history that would never be seen again.

It was a poignant and distressing sight. How quickly and easily had this animal, which lived here for tens of millions of years, been driven to extinction.

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It’s hard to fund a good word written about bats, and even then the closest you get is a grudging admiration for their fabled wiliness. No other mam­mal has been so connected with the supernatural, bad luck and death. Thanks to Bram Stoker’s 1897 creation of the dripping-fanged Count Dracula, and the many filmswhich took up that theme, bats are forever linked in the popular imagi­nation with vampires. In ancient Mayan mythology the underworld was ruled by a terrifying bat god, and bats have been associated with evil and the supernatural in western culture at least as far back as the Bible. Oddly, considering the anti­pathy toward them in most other cultures, the Chinese have always seen them as good luck symbols rep­resenting the five greatest joys of hu­manity: health, happiness, longev­ity, prosperity and contentment.

Most of the anti-bat sentiment has to do with the curious duality of an animal which flies like a bird yet has fur and teeth like a mouse. In one Aesop fable a bat is snared by a weasel. Pausing for a moment before eating the bat, the weasel explains that it eats only birds. Sharp as a tack, the bat tells him that he is in­deed not a bird, but a mouse. Reluc­tantly, the weasel lets him go. Later, the bat is caught by another weasel, one that eats only mice. This time the crafty bat extricates himself by saying that he is a bird. But in these tales, deceit must be punished, and eventually the bat is banished for­ ever to the night. This link with darkness, and our fear of the dark, has probably been the main reason for the connection between bats and evil through the ages.

Indeed, bats have had such bad press over the years that interna­tional conservation organisations have been reluctant to go in to bat for them, so to speak. They see the task as being simply too hard. Bats do not meet the heart-tugging crite­ria for fundraising campaigns. They elicit such a revulsion in people that the head of Bat Conservation Inter­national, Mervyn Tuttle, has been reported as saying despairingly: “People want them to become ex­tinct. I could probably raise 10 times as much money if I promised people to get rid of all the bats in their area instead of asking them to help me save them.”

In Australia, fruit bat colonies are systematically exterminated by orchardists, despite pleas from bi­ologists that the bats have immeas­urable worth as pollinators of cer­tain fruit and, ironically, most of the eucalypt species on which the Aus­tralians’ beloved koalas feed. Here, our short-tailed bats have recently been found to pollinate the rare Dactylanthus taylorii or wood rose, a strange parasitic forest plant, and it is thought that other plants may also be bat-pollinated.

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One night, with the aid of miners’ lamps and a night vision ‘scope of the kind much used in Vietnam, I watched a group of six short-tailed bats in a study enclosure at Wellington Zoo with re­searchers Jay McCartney, a student from Massey University, and the De­partment of Conservation’s Brian Lloyd, both of whom are studying the bats’ diet, along with other as­pects of their biology.

Two of Brian’s particular concerns are finding out whether short-tailed bats will eat 1080 poison (used for possum control operations) and the anticoagulant poison brodifacoum, used to eradicate ro­dents on offshore islands. If it can be shown that they will not touch the latter, it will be used to clear Little Barrier and Codfish Islands of their last remaining bat enemy, the native kiore rat. And if the eradication is successful, the bats will again have a safe haven. The results so far look cautiously promising: the bats have shown no interest in the poison. But it is still too early to know if they could be affected by eating insects which have somehow come into contact with poison baits. Both bat species are prodigious insect eaters.

Brian carefully lifts one bat out of its roost. It looks about the same size as a long-tail, only much chubbier. Close up, its brown fur is short and thick-piled. It has a piggy little face with beady eyes, a snub snout and a mouthful of prominent sharp teeth with which it now bites Brian. He swears. Enthusiastic nonetheless, he tells me to notice its legs: “See how sturdy they are compared with the legs of long-tailed bats? That’s be­cause these ones run around the ground and climb trees.” As Brian loosens his grip to show me, the bat bites him again. Researchers of long-tailed bats talk smugly of the sweet, non-nipping nature of long-tails compared with the short tempers of their ancient cousins.

In his central North Island study area, Brian has found roosts of up to 2000 short-tails in one tree. Such roosts are large for our bats, but are nothing compared with some over­seas species. A popular location for vampire film makers, the Carlsbad Cave in Mexico, is home to over 20 million Mexican free-tailed bats. Each dusk they swirl out for three hours in a ribbon 20 metres high and 10 metres wide, while on the guano-covered floor of the cavern below a seething mass of snakes and insects waits hungrily for juvenile bats to fall from their precarious toe-holds.

Both species of New Zealand bat prefer holes in old forest trees; they do not roost in belfries, barns, or any other buildings like the opportunis­tic European bats. Occasionally, however, they do roost in caves.

They are peripatetic, having no par­ticular yearning to return to the same home each night, nor any alle­giance to any particular group, and certainly none to a mate.

The short-tailed bats we are wait­ing for in the zoo tonight will emerge later than the long-tails, which come out right on dusk and for about an hour afterwards. These ones wait until it is quite dark, a couple of hours after sunset, Brian tells me. While we wait, with the howling of timber wolves and other night sounds of the zoo around us, he fills me in on some other bat facts, revel­ling in the details of bats’ remark­able biology. For a start, he says, they are heterothermic, having the ability to alter their body tempera­ture according to need. Like com­puters, they can shut themselves down to save energy—dropping their metabolic rate to as much as a few hundredths of the normal active rate. In effect, they hibernate.

“Their body temperature can go down to ambient,” he says. “Over­seas, a hibernating bat was found with a temperature of minus two de­grees Celsius. I read of an experiment where researchers kept a bat in the fridge for 350 days. When it emerged it was perfectly healthy.”

Both New Zealand bat species possess this ability to adjust their metabolism—a particularly useful adaptation to have during winter, when bad weather makes the likeli­hood of finding food small. Unlike some deep hibernators, they can wake up, drink, fly about, even change roosts on odd mild days in winter, but basically they are in hi­bernation for three to five months between April and August.

“Even in summer, short-tails go into long periods of torpor. I’ve had bats that haven’t moved for about ten days. When we’re netting them, even after only 20 or 30 minutes in a net on a cool night, they will go into torpor. The first time it happened to me I thought, ‘Oh no, the bat’s died!’ After a few minutes in my hand they wind themselves up into action.”

As we talk, the short-tailed bats finally spill out of their artificial roost, a small box open at the bot­tom. If ever a bat illustrated the bird/ mouse duality it is this bat. Unlike Emily and her long-tailed brothers and sisters, which are aerial feeders and tend to graze the roomier forest canopy and grassland edges, short-tails negotiate the forests’ tangled undergrowth closer to ground level. Watching them twist and bank through the branches in the enclo­sure, you can see that their ability to aerodynamically fine tune their rub­bery wings makes them much better fliers than birds are. Jay McCartney tells me admiringly that he has watched them fly figures of eight through the rungs of a ladder he’d set up in the enclosure.

Suddenly and disconcertingly, one drops to the floor, briskly folds its wings and, like a little hobgoblin, scampers up branches and along the floor, looking for beetles to crunch. Then two of them dive under the leaves and start rooting about like minuscule piglets, erupting from time to time through the covering litter. We all laugh at the ludicrous sight: “They look like mice on crutches,” Jay says. These bats eat moths, crickets, beetles, nectar and, in captivity, mealworms. Vast quan­tities. On an average night, Brian in‑forms me, they eat about 100 mealworms between the six of them—around five grams of food each. That’s about a third of their body weight, and in my terms that’s roughly equivalent to eating 20-plus kilograms of food a day.

The air is full of ticking noises from the bat detector as the bats cir­cle their prey, then dive on it. “Bats turn off their hearing for the few mi­croseconds’ duration of each ultra­sound pulse, then turn it back on again,” says Brian. “Were they not able to do this, they would deafen themselves. Emitting those pulses from inside your head is equivalent to standing a few metres away from a Jumbo jet during take-off!”

Bat echolocation is precise enough for the animals to tell the difference between solid objects and fluttering ones. Bad luck for insects. But in an exquisite fairness of na­ture, many moths can pick up the bats’ frequencies, and therefore have a fighting chance, albeit a slight one. When they detect a bat homing in, they spiral earthwards in a typical dogfight manoeuvre. Or else they play dead. In a further twist to this contest, some species of bats also know what the moths know, and compensate by either switching off their echolocation at the last mo­ment, or increasing their flying speed to snatch the moth before its brain computes the imminent mes­sages of death. Scientists call this kind of tit for tat the evolutionary arms race.

In our enclosure the bats were the clear winners, audibly crunching and slurping through the beetles and mealworms, and occasionally wing­ing away to snatch a moth which, unable to get out of the enclosure, had tried to make a dash for it any­way.

In September, the first batling bred in captivity was born here at the zoo. Abandoned at birth, it had to be hand-raised, and lived for five months before succumbing to dis­ease. This year, researchers of both bat species have confirmed that the females give birth in December and January, but beyond this fact little about their life histories is known. It seems that long-tailed bats bear only one offspring per year—unlike other mammals of comparable size, which produce large clutches, but consist­ent with similar long-lived crea­tures. Batlings can readily be aged up to the first six weeks, because it takes this long for the joints between the finger bones to mature.

Another recent discovery, made by Colin O’Donnell and Jane Sedgeley in Fiordland’s Eglinton Valley, is that long-tailed bats have nursery colonies, in which females group together while they are rais­ing their young. Like normal roosts, the colonies appeared to move to a new location each night. Each day, Colin and Jane found baby bats at new sites, and assumed that the mothers must be picking up their offspring and carrying them from one place to another. This year, Colin and the researchers with him saw astonishing confirmation of that fact.

“One night in January we caught a batling in the net. It was still un­able to fly, so we knew that its mother must have been carrying it. After we’d weighed all the trapped bats, we put them in a bag, hoping that the mother and baby would find each other. But when we released them, we found that the baby bat was left on its own. We were stand­ing there with it, wondering what to do, when we noticed one bat return­ing to circle around us. She flew down and landed on the hand of the person holding the bat. She did it twice more, and then on the third time she scooped the baby under her wing and flew away with it.”

Marvelling later at their good for­tune at having seen such a rare event, the scientists realised that the mother, which had been weighed at 13.5 grams, had picked up a baby which was 7.5 grams—almost two thirds her own weight.

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Dusk was drawing on when, late in March, I took a seat in a grove of kidney ferns on the forested flanks of Little Barrier Island. I was about to experience a sound and sight few other New Zealanders had ever witnessed: the mating ritual of our short-tailed bat.

His face alight with anticipation, the island’s conservation officer, Chris Smuts-Kennedy, pointed at a small hole two metres up a slim rewarewa. “He’ll be here soon,” he said.

Chris and his wife Robyn have made this 3000-hectare Hauraki Gulf island their home for the past four years. It’s one of the few islands in New Zealand which are now al­most free of introduced predators—only the kiore rat remains. The sound of birdsong is so loud that

you can hear it several hundred me­tres out to sea as you approach by boat. Sitting in his lounge earlier, Chris had pointed, amused, to the windows, where a fringe of watchful kaka parrots hung upside down from the spoutings, like women’s gaudy earrings strung across the windowpane. The misty hilltops are now home to another New Zealand parrot, the cat-sized kakapo.

It had been an exhausting two­and-a-half-hour climb, much of it with the aid of rope, up the loaf-shaped island to the study site. We were now 400 metres above sea level, among kauri, beech and rewarewa. At the base of the trees, pompoms of white lichen looked like half-melted drifts of snow. Dark­ness would fall soon, and as the light faded I noticed a weak blue glow at our feet. A fluorescent fun­gus, Chris explained.

We had our usual bat-hunters’ tools: night vision ‘scope, head­lamps and bat detectors. But tonight we would be able to hear the singing with our own ears, Chris assured me.

Chris investigated the hole in the rewarewa, poking a stick into the opening. It tunnelled upwards for at least a metre.

“About half an hour after dusk one male bat will fly into the hole, and he’ll start singing. That’s the sig­nal to the females that he’s in resi­dence and available,” Chris said. Last year, while looking for kakapo, he had heard the singing of a number of bats within a 40-metre radius. Two nights before my arrival, he and his daughter Marie had brought their sleeping bags up and stayed the night to see if the bats were, as he predicted, back at the singing holes this year. He had tracked the noise to two singing sites, and this was one of them.

While we waited in the steadily chilling night, Chris adjusted the knee bandages which testify to the toll this gruelling terrain takes on human bodies. He has just joined the list of conservation officers hav­ing to have knee operations for a condition that’s been nicknamed “Little Barrier knee.”

The main aim of his research, he whispered to me, is to find out what time of year mating, parturition and fledging of short-tailed bats happens on the island. And as he studies

these things, he’ll be checking the distribution of the bats to see how it varies according to seasons, weather, time of night, temperature, phase of moon and altitude.

The link between this autumn mating time and the births in sum­mer is almost certain, Chris ex­plained. But bats can’t be pregnant for all that time, which means that the pregnancies are being delayed in some way. One of two systems could be taking place. The first is delayed implantation of the fertilised egg—the egg is fertilised in autumn and then just sits in the uterus without implanting in the uterus wall until the gestation period, probably one to three months before birth. The other system is sperm storage, where the egg is not fertilised, but rather the sperm is stored in the bat’s uterus or vagina, and fertilisation and implantation happen after win­ter in rapid succession. Both sys­tems are known to occur in overseas bats. This very efficient way of breeding isn’t uncommon in mam­mals. Seals come ashore, give birth and then mate straight away, thereby fulfilling all their breeding needs in one trip ashore.

Chris paused in mid-explanation. “There he goes,” he whispered. At first I heard nothing. Then I realised that the small piping noise, some­thing between a chirping and the sound of someone smacking their lips, was our hopeful bat.

At 27 kilohertz on the bat detec­tor, there he was, loud and clear, a stream of blips signalling the higher frequency part of the call. In the dim light of a red-filtered headlamp we could see the bat’s head, poking comically out of the hole—a small mousy head not much bigger than the top joint of my thumb, with its big ears and a handsome moustache. Sensing our movement, the head snapped back into the hole, but within seconds the lovesick little runt’s face was back out again, sing­ing its jovial tune. To females of his own kind, the music was hopefully as seductive as an aria from Jose Carreras.

Mike Daniel first heard the dis­tinctive songs when he was working in the Codfish Island forest. The chirping call was audible for 20 to 30 metres, and when he tuned his bat detector to the bats’ frequency he could pick up a series of clicks and melodic warbles coming from inside small tree holes. Over two years of observation, he found that there were usually six or seven singing trees spread over about 50 metres, one bat to each tree—”hot shots on hot spots” was how Daniel de­scribed the sites. When other males approached the trees they would be greeted with angry chatter, and Dan­iel found that the resident bats spent so much time coming out to chase off the competition that occupancy would be snatched off each of them every two hours or so. When females approached the holes, though, the male bats would become exceed­ingly vivacious. If a female liked the sound of his tune (and she often doesn’t) they would mate, and then she’d fly off while he launched back into song, awaiting the next tryst. As one naturalist drily remarked: “It’s not unlike the human bar pick-up scene, really.”

This means of courtship—where the male stays in one place and fe­males visit to mate—is called lekking. Kakapo display a similar behaviour, the males sitting in bowls they have scraped in the earth and booming out calls full of longing.

Scientists find it rather strange that short-tailed bats choose to mate this way. Unlike kakapo, which are loners and so need to send the mes­sage out seeking female company, these bats hang around together in roosts the entire year. Why, then, are they driven to go and find these trees—used for neither roosting nor breeding—and plead so cravenly for sexual partners?

Suddenly there was a quiet rus­tle, a swirl of air, and like a feather brushing my hair the bat skimmed past. A musty smell, like ammonia, lingered for an instant. Presumably he was off to join his kin at their next roost. Which made me recall something Colin O’Donnell had told me, and left an even odder unan­swered question. “I had put a trans­mitter on a young bat, and after a short time out flying she had gone back to a tree roost where she spent the rest of the night. Then, about half an hour from dawn, she flew out, and by the time it was daylight she was in another tree. And that’s where the other bats arrived soon afterwards.”

Had they somehow agreed on a prearranged spot to meet? How did that young bat know where to go otherwise? And how does this male short-tailed bat, which we had just observed, know in this whole island of trees the exact tree in which he will find his fellow bats? How do bats “tell” each other these things?

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A week after our first visit to the patch of Napier bush where we had found Emily, scientist Tony McCann tele­phoned. He and Nick had been tracking her for a week and a half, and had found her at three different roosts, all within 500 metres of where we’d caught her—quite close, considering roosts can be 15 kilometres apart. At first, she roosted on her own. Then, two nights later, she had been found with a large roost of 115 others, sev­eral hundred metres away from the first tree. Two nights later they found her at a third roost, again with more than a hundred others.

Her transmitter was losing power, and there would only be a couple of nights left before they lost the sig­nal—and her—altogether, he said. If we wanted to try to get photographs of a roost we should come now.

The following night, the canopy of podocarp forest hanging like a cathedral above us, stars prickling the black gaps, photographer Michael Schneider set up his cam­era gear and we awaited the emer­gence of the bats. The roost was in a hole five centimetres wide, about four metres up a dead matai tree. By putting an extension ladder up the tree Michael could set up his camera just half a metre below the roost.

On our receiver we could hear the faint ticking of the transmitter on Emily’s back. The bats had come out of their previous night’s roost at 9.13 P.M., still an hour away. Tonight, with days shortening, they would probably come out a few minutes earlier. There was no way of know­ing whether Emily was sharing this sleeping place with others or whether, again, she would be on her own.

At 9.05 P.M.we hear the first pee­vish signs of a sizable colony com­ing to life—the squeaks clearly audi­ble four metres below. Then, with­out warning, bats start pouring out of the hole: 10, 30, 40, and still com­ing. We lose count. The stream of static on the bat detector sounds like a crowd at a football match. Still they pour out, their wings strobing in our torchlight, disappearing off to some unknown hunting ground.

And then they have gone, and with them, somewhere in the crowd, “our” Emily. We watch for two hours until the first bats return for a rest, coming in like planes awaiting landing orders, circling the tree in a spiral and then zeroing in with deadly precision to disappear at full speed into the tiny hole.

As we switch off the noise of the bat detectors, abruptly the stealthy silence of the bush descends, returning us to the prison of our own senses, the only noise the mournful call of the morepork, reminding these deadly hunters that they, in their turn, are the hunted.

Next night, back in Auckland, back in the world where people shudder at the thought of bats, I am sitting in a Ponsonby Road bar watching the nightlife of a city come out. A man with fishnet stockings and a blonde wig is crossing the road. A group sitting at the next ta­ble, all in black, their faces a deathly pallor, remind me uncannily of vam­pires.

My watch says it is 9.05. In a few minutes, far away in the forest, the bats will be flying.