Voices in the Dark (C2 Reading Story)

C2 · MASTERY Reading practice · ~3,170 words · 22-min read

This is an original short story for advanced learners at C2 level. It is a quiet piece of science fiction that isn’t really fiction — a field scientist in a remote Scottish valley notices that the local bats are calling at the wrong pitch, and has to decide how much she trusts her own ear. Read the nine key words first, then take your time with the story. The rest of the world will still be there when you finish.

The story

1 · The frequency

Iris Halloran had been listening to the wood for so many summers that she could pick out the shape of a silence before it arrived. Give her a July evening in Glen Cathair, thirty seconds of tape, and she could tell you the wind’s direction, the height of the water in the burn, and whether the resident tawny owl was in its usual roost or had drifted west towards the deer forest. Colleagues sometimes teased her that she had a bat’s ears. This was, in her line of work, a compliment.

She was a bioacoustician, which is the least glamorous word in ecology — nine syllables of it — but the one she wore most cheerfully. Her research concerned the ultrasonic calls of British bats, and Glen Cathair was, by her own quiet reckoning, one of the most acoustically pure valleys left in the country. No motorway hum. No wind turbines within earshot. Only the peat, the birch, and the wide, echoing throat of the glen itself. In the fourteen summers she had come here, she had recorded 2,400 hours of the wood after dark, and she had almost begun to feel that the wood was letting her, at last, hear something on its own terms.

That August, however, something was wrong.

She noticed it on the second night. She was in her tent, headphones on, half a mug of thin coffee going cold beside her, pulling the day’s spectrograms up on her laptop for a quick pass before sleep. A spectrogram is a picture of sound — frequency on the vertical, time on the horizontal, the loudness of each frequency shown as a smudge of colour. To the untrained eye, it is a mess. To Iris, after twenty-nine years, it was a page of ordinary handwriting. She could read a bat call at a glance and tell you within a kilohertz what the animal was and roughly what it had been doing.

Something on the screen made her pause. She played the file back at a tenth of speed, the ultrasonic clicks dropping into a soft, wooden knocking she could hear with her own ears. She frowned. She played it again.

A pipistrelle. Almost certainly a soprano pipistrelle, one of the tiny common bats of the British summer. But the peak frequency of its echolocation call was 52 kilohertz. Which was — she leaned back, working it out — three kilohertz higher than any pipistrelle in Glen Cathair had any business calling at. Not by a hair. By a whole octave of a bat’s small musical world.

She sat with that anomaly for a long minute. Then she rubbed her eyes and told herself it was probably a rogue individual — a slightly odd little male, or an artefact of the microphone. She saved the file, labelled it, and closed the lid.

The next night the frequency was there again. And the night after that. By the end of her first week she had seventeen recordings of pipistrelle calls sitting a full three kilohertz above the historical mean for the site, and not one, so far, at the ordinary value.

Something in the wood, or in the animals that used it, had quietly changed pitch.

2 · Fourteen summers of tape

She telephoned the office in Edinburgh from the pub that Saturday, the only reliable signal being at the far end of the car park where the road curved to meet the sea loch. Eliot Duthie, her postgraduate student, answered on the third ring, sounding faintly annoyed to be reached on a weekend. She apologised in the abstract, without meaning it.

“I want you to pull the pipistrelle files. All of them. Cathair, 2010 through last year.”

“All of them?” A pause. “That’s the best part of two terabytes.”

“I don’t need you to listen. I need you to run mean peak frequencies by season and by year and give me a plot by Monday.”

There was another pause, longer, in which she could hear him doing the arithmetic of how much of his weekend she had just consumed.

“Iris — is something wrong?”

“That is what I’m asking you to help me find out.”

She hung up and stood a moment in the drizzle, looking down at the loch, which held the low light of the evening like a plate. She was sixty-one years old and had been careful, all her professional life, not to become the kind of scientist who fell in love with a hunch. Once, as a young woman at Aberdeen, she had watched a supervisor of hers ruin her reputation over a call she made in a hurry — a claim about the northern range shift of a species that turned out, when properly checked, to be an artefact of a broken microphone. Iris had learned early to hold her observations at arm’s length until they had been beaten flat by scepticism, her own first of all. It was, in her book, the tacit contract of being a scientist: you did not marry your first idea.

The Aberdeen affair had gone like this. Her supervisor, a woman she had loved for her boldness, had built an entire seminar paper around a two-week run of anomalous data. The northern range of a certain warbler, she had said, was shifting; here was the proof; here were the recordings. The room had believed her, because Rosemary was believable. A month later a technician in the workshop, cleaning the equipment for the winter, pointed out that the primary microphone had been faulty from about the fourth day of that run — a small resonance in the diaphragm which produced exactly the acoustic signature Rosemary had taken for a warbler’s call in an odd place. It was not fraud. It was worse than fraud, in the small local world of that department; it was carelessness. Iris had watched a career quietly close over the following two terms — a couple of retracted talks, a series of coldly polite silences at conferences, and then, in the end, a sabbatical from which Rosemary had never really come back. It had left Iris with a particular allergy — the allergy of someone who has seen a good scientist become a cautionary tale — and a lifelong preference for slow findings over fast ones.

Yet fourteen summers of tape is not a hunch. Fourteen summers is a longitudinal record; it is, in fact, the sort of dataset a researcher would ordinarily kill for. If the pipistrelles of Glen Cathair had drifted three kilohertz upward, the tape would say so, and it would say so with rather more authority than her ear.

Eliot’s email arrived at ten to eleven on Sunday night. She was reading in the tent by the light of a small lamp, and the little chirp of a message coming in through the satellite hotspot made her jump. Attached was a single plot: fourteen dots on a graph, one for each summer, plotting the site’s mean peak frequency of soprano pipistrelle echolocation against the year.

The dots formed a line. It was not a scatter; it was not a mess. From 2010 to 2019 the calls sat comfortably around 49 kilohertz, with the small annual wobble one expects of a small mammal population. From 2020 the line began to lift. Half a kilohertz. A kilohertz. By last year the mean had climbed to 51.4. This year, on the strength of her first week’s recordings, it was already 52.1.

Under the plot, Eliot had written a single line: “Is this real?”

Iris looked at the graph for a long time. Then she wrote back: “I don’t know yet. But it’s not not real.”

3 · The suspects

There is a version of the scientific temperament that thrills to a discovery in the way a hound thrills to a scent. There is another, less-loved version that treats every discovery as a suspect to be interrogated. Iris belonged, with only rare lapses, to the second school. What she wanted to know, before she wanted to know anything else, was what could produce a false signal like this one. Bats, unlike stars, are not immune to observer effects.

She listed the candidates on the back of an ordnance survey map, which was the largest clean paper she had to hand.

First: the equipment. Over fourteen years she had replaced her ultrasonic microphones twice, once in 2016 and once in 2022. Neither replacement corresponded with the shift. Neither cluster of new equipment produced a step in the curve; the drift was smooth and gradual. Rule that out.

Second: the recorder settings. The sample rate had been constant since 2010. The gain, calibrated against a reference tone every May, had been within a decibel of itself throughout. Rule that out.

Third: the identification. Perhaps she had been fooled, and what she had taken for sopranos were in fact some closely related species with a naturally higher call. The obvious candidate was the common pipistrelle’s cousin, the Nathusius’ pipistrelle, a migrant with a slightly lower call than the soprano. That worked against her theory rather than for it. Rule that out.

Fourth: the population itself. Perhaps the local sopranos had, in fourteen years, been quietly replaced by animals from elsewhere with a genetically higher call — a slow demographic churn. This she could not immediately rule out, though it was implausible. Bats are homebodies; the maternal roosts of Glen Cathair were, she knew from the bat group’s ringing records, remarkable for their stability.

Fifth — and this was the one that made her put the pencil down — perhaps the bats themselves had adjusted. Perhaps, over fourteen summers, they had slowly retuned their calls upwards in response to a persistent low-frequency change in their acoustic environment. Perhaps, in short, they were hearing something we were not, and they were talking above it.

She sat with this for a while, watching the moths tap softly on the tent’s fabric. It was the kind of hypothesis that, twenty years ago, she would have laughed out of the room. Bats were, in the old textbooks, exquisite but essentially fixed instruments; their calls were species-typical, hard-wired, and about as culturally flexible as a violin. That view was no longer quite so dogmatic. In the last decade a modest but growing literature had documented small vocal adjustments in bats and in songbirds in response to urban noise. Never, so far as she knew, at this magnitude, and never in a place as quiet as Glen Cathair. But not impossible, either.

What, then, in Glen Cathair, might have been generating a persistent low-frequency change over a decade? She thought of the wind farm — the one twenty kilometres to the north-west, commissioned in the summer of 2019. Twenty kilometres was a long way for infrasound, but not an impossibly long way. Sound travels further than we tend to think. And 2019 was, uncomfortably, when her curve began to lift.

She wrote it down. She underlined it once — not twice. Then, being Iris, she wrote next to it three alternative explanations she had not yet tested. To corroborate anything would require far more than her ear and her graph. That much she knew before she had finished her tea.

4 · A question of proof

Eliot arrived on the Wednesday of the second week with a boot full of equipment and the earnest weariness of a man who has driven from Edinburgh in one push. He set out his kit in the tent porch — a second recorder, a set of calibration tones, a small infrasound sensor she had asked him to bring — and looked up at her, waiting for orders.

“I’ve been thinking,” she said, “about how one proves this.”

“Or doesn’t.”

“Or doesn’t. Yes. Rarely have I felt more strongly that the second is at least as important as the first.”

She sketched him a plan. They would deploy the infrasound sensor for a fortnight in the glen and again at a control site — a quiet valley thirty kilometres west, well beyond any conceivable turbine reach. They would record pipistrelles simultaneously at both. If Glen Cathair alone showed elevated call frequencies, and if Glen Cathair alone showed measurable low-frequency energy at the infrasound end, the hypothesis would begin, cautiously, to breathe. If both valleys showed the shift, then the cause was general — climate, perhaps, or something else entirely. If Cathair showed the shift and the infrasound record was silent, then the wind-farm story was out and something more local was in play.

“And if none of the above,” Eliot said, “we go home puzzled.”

“We go home honest. That is not the same thing as going home puzzled — but it’s not the worst outcome either.”

He grinned, the first grin she had seen from him in a fortnight. He was, she thought, growing into the work.

They ran the fieldwork through the last week of August and the first two weeks of September. The nights were sharp; frost had begun to lie by morning. The bats fed with the small manic hunger of animals preparing for winter, and Iris and Eliot lived on porridge, thermos coffee, and the deep pleasure of a plan being executed properly. In the daytime they walked the hillsides for a change of scene, and once or twice ate a good dinner at the pub. Neither of them mentioned publication.

On the fifth night of the two-site deployment Iris sat up until three in the morning watching the spectrograms come in from the control valley in real time. The calls dropped into place at 49, sometimes 49.2, sometimes 48.8 — the small, satisfying wobble of a population that had not been asked to change anything. The Cathair feed, on the second screen, sat implacably above 52. She had not, until then, been quite sure which of the two feeds she wanted to be surprised by. She discovered, at three in the morning, that she wanted the control site to be dull. That, she noted with the small wry honesty which is a scientist’s most private virtue, was itself a small piece of evidence — evidence about the state of her hypothesis, and about the state of the person holding it.

By the end of the third week they had their answer. The control valley’s pipistrelles called at 49.1 kilohertz, indistinguishable from Cathair’s ten years ago. Glen Cathair’s called at 52.3. The infrasound sensor at the control site sat, all night, on a very quiet baseline. The one at Cathair showed a small but persistent broadband hum, peaking below 20 hertz — below human hearing, well within pipistrelle sensitivity. It was not enormous. It was, however, very much there.

Eliot was elated. He was ready, that same evening, to write a preprint. Iris, who had waited fourteen summers for this data, was not.

“We have,” she said, “a correlation between an environment and a call frequency, in one glen, with one control site. We have, as of tonight, one season of infrasound data. What we do not have is a mechanism, we do not have replication across sites, and we do not have any way of separating a wind-farm signal from any other regional infrasound source. We’re a long way from a paper.”

“Iris — “

“You want to be quoted in the Guardian. I want to be right in ten years.”

He looked at her, and then he laughed. It was, she thought, exactly the right laugh — the sort of laugh a young scientist has, when a lesson lands.

5 · First light

They stayed in the glen until the first of October. Not once did they stop recording. Not once, either, did Iris pretend to herself that she was not excited; she had never claimed to be unmoved by her own field. What she claimed was only that she would not be moved so far by it that her feet left the ground.

On the last night they packed slowly. There was frost on the tent, and stars in a pale blue-black band above the ridge, and beyond the ridge a thin, growing light where the day was, in some technical sense, already beginning. She stood a long time at the door of the tent, listening to the wood, and it seemed to her that she was hearing the glen not as she had heard it fourteen years ago — as a wild, given thing, delivered to her ear entire — but as something that answered to the world beyond itself, and always had, and that she had been slow, all this time, to notice.

Eliot came out with two mugs of tea and handed her one.

“Where do we go from here?” he asked.

“Two more field seasons at Cathair, at least. Three more control sites. A proper phenology of the roost — I want to know when the calls shift each year, and by how much, and whether they lift with the turbines’ output. A physicist to explain the infrasound propagation properly. A statistician to eat me alive if I’ve got the model wrong. And after all of that, a paper — but a slow one, mind you. A slow one.”

He nodded. Neither of them said anything for a while.

“Do you think it’s the turbines?”

She sipped her tea and considered the question in the honest way she had been taught, forty years earlier, to consider questions.

“I think it’s more likely than not,” she said, “that something in the low-frequency environment has changed here, and I think it’s more likely than not that our bats are dealing with it in the only way a small animal can. I think the turbines are a plausible candidate. I do not yet think the case is made. That is not the same as saying the case will never be made.”

He accepted this without pressing. He was, she thought, going to be all right.

They stood in silence a while, tea steaming into the cold. Somewhere up the ridge a red deer barked once and then, thinking better of it, was quiet. Iris found herself, unexpectedly, close to tears. It was not the finding, she told herself; that would be indecent, at this stage. It was the sudden knowledge that after fourteen summers her method — the patient, unfashionable, deeply unsexy accumulation of long-run tape — had earned itself, at last, the right to ask a very large question. Whether the eventual answer turned out to be turbines or something quite else, the question was now hers to ask, and hers to be careful with. That, she thought, was worth a moment on the tent step at first light.

They drove out of the glen with the sun coming up behind the birch, and pipistrelles — the last of them, the late ones — twisting up out of the ancient roost above the old stone barn, their calls too high for either of them to hear.

Only when she reached her office that evening did Iris allow herself, at last, to write down in her notebook what she had been telling nobody — least of all herself — for the whole fourteen summers: that the world she had been listening to had been changing all along.

Not once, in fourteen summers, had she really been listening to only the bats.

Check your understanding

Read each question. Think about your answer. Then click “Show answer” to check.

Words to remember

Here are the nine key words again, in fresh sentences that put them into a wider range of contexts. Notice, at C2, how many of them are as at home in academic prose as they are in serious journalism.

• bioacoustician — The bioacoustician spent most of her career three metres up an oak tree with a directional microphone, and would not have swapped it for a professorship.
• echolocation — Dolphins use echolocation not only to hunt but, some biologists now argue, to share information about the shape of an object with other members of the pod.
• ultrasonic — Modern rodents can navigate quite happily in what, to us, is silence: their world is a rich ultrasonic tapestry that we simply cannot perceive.
• spectrogram — A trained ornithologist can identify a warbler from three seconds of spectrogram even before they play the audio.
• anomaly — For a decade the reading was dismissed as an experimental anomaly; only when a second team, using different equipment, reproduced it was the effect taken seriously.
• phenology — The great virtue of long-run garden diaries is that they are, unwittingly, an amateur phenology — a record of when things bloom, arrive and leave, kept before anyone had a word for it.
• corroborate — The witness’s account was compelling, but the court would not act on it until physical evidence from the scene came in to corroborate the story.
• tacit — There was a tacit understanding around the office that nobody discussed the audit before ten o’clock in the morning.
• dogmatic — He was too fine a scientist to be dogmatic about any of it — every claim, however cherished, was, in his own phrase, “provisional until further notice.”

Talk about it · Write about it

Talk about it: Iris insists on caution even when the evidence is beginning to line up. Is her patience wise, or is it the kind of over-caution that lets important findings sit on the shelf while the world moves on? Have you ever seen someone be “right in ten years” — and if so, was it worth the wait? Is there a place, in your own working life, where you feel the pull between speaking up quickly and being sure?

Write about it: In about 200–250 words, write an internal note from Eliot to Iris six months after the story ends. In it, he proposes the design of a second field season across three new control sites, and argues — respectfully — for one methodological choice that Iris might not immediately agree with. Try to use inversion at least three times (“Not until we have three seasons of infrasound data…”, “Only then can we…”, “Rarely does one find…”), and to hedge your claims in the C2 register the story models: it may be that, one might argue, on the evidence available, tentatively, provisionally.

Congratulations — you’ve just read a full C2 short story of just over three thousand words. Notice how much of the difficulty here wasn’t in the vocabulary at all, but in the register: the dry humour, the scientific hedging, the way information about Iris’s past arrives sideways rather than through direct statement. That, more than any single word, is the reading skill C2 asks for.

But we’ve left a great deal in the air. Iris talks of “two more field seasons,” of physicists and statisticians and a paper five or ten years off. What happens when the paper is finally written — and what happens when a small, careful finding about bats in a Scottish glen collides with a policy debate about renewable energy that is anything but small or careful? That is a very different story, and one worth telling next.

Next story: Read another C2 story →

About this story: This is an original C2 graded reader (~3,170 words). At C2 the vocabulary control loosens to near-native range — idiom, register shifts, dry humour and hedging are all in play — so instead of “the 1,400 most common words,” the guiding target is that a C2 reader should follow roughly 98% of the running text on a first pass, with only genuinely specialist terms (bioacoustician, echolocation, spectrogram, phenology) glossed up front and reused inside the story so you meet them at least twice. The featured C2 grammar is inversion for emphasis, which is used sparingly and deliberately in the narration.

Khamis Maiouf

My name is Khamis Maiouf. I am the creator of the English Teacher Site, dedicated to providing valuable resources and insights for students around the world. With a passion for education and a commitment to helping students enhance their skills, I aim to make English teaching more effective and enjoyable for both educators and students.