Twenty-Three Minutes of Chewing, One Kilometre Up

A Guano Pile That Started an Argument

Doñana sits at the southwestern corner of Spain, marshland and pine and cork-oak scrub tucked against the mouth of the Guadalquivir, and every autumn the sky above it fills with something that never touches the ground there: millions of small songbirds flying south at night, on their way to Africa. Below them, in tree hollows and old buildings, roosts one of the stranger residents of the same landscape. Nyctalus lasiopterus, the greater noctule, is the largest bat in Europe, with a wingspan that can reach 46 centimetres [9] — large enough that, seen well, it does not look quite like the bat you are picturing.

Greater noctule colonies at Doñana are themselves an unusual social system to be attached to this story: the same research group has mapped their roost-switching as a highly structured fission–fusion network, individuals splitting into and rejoining different tree-cavity groups on a pattern closer to what is normally described for primates than for bats [6, 7]. It is the same population, and largely the same research lineage, that later supplied both the isotope case and the recording that closed it.

In 2001 Carlos Ibáñez and colleagues published something odd about it. Faecal pellets collected below greater noctule roosts contained bird feathers — not a trace, but a recurring, seasonal presence, timed to exactly the weeks when the migratory songbirds were passing overhead at night [2]. A bat roost accumulating bird feathers is not, on its own, proof of anything in particular. Birds die of all kinds of causes during a migration that can run thousands of kilometres: exhaustion, collision, cold snaps, other predators. A bat that scavenges an already-dead bird off a branch or the ground would leave feathers in its droppings too. The 2001 paper could establish that greater noctules were, somehow, involved with dead birds. It could not establish whether the bat was the reason the bird was dead.

That distinction is not pedantry. It is the whole scientific question, and it stayed open for twenty-four years.

What the Isotopes Could Prove, and What They Couldn’t

The next piece of evidence, in 2007, came from chemistry rather than a scale or a scope. Popa-Lisseanu, Ibáñez and colleagues measured stable carbon and nitrogen isotope ratios — δ13C and δ15N — in greater noctule blood and fur, and compared them against reference values for the two candidate food sources: flying invertebrates, and the passerine birds migrating overhead [3]. Isotope ratios work as dietary tracers because an animal's tissue chemistry echoes what it has been eating, with a fairly predictable offset at each step. A diet of birds and a diet of insects come from different points in the food web and carry measurably different signatures.

The paper's own numbers make the separation vivid. Passerine tissue: δ13C = −22.43 ± 0.32‰, δ15N = 9.60 ± 0.26‰. Invertebrate tissue: δ13C = −25.64 ± 0.23‰, δ15N = 6.45 ± 0.39‰ [3]. Subtract one from the other — our own arithmetic, not the paper's — and the two diets sit 3.21‰ apart in carbon and 3.15‰ apart in nitrogen, which is a wide gap by the standards of this kind of measurement. Autumn greater noctule blood, the paper reported, fell in the lower part of the theoretical box that represents a nearly pure-bird diet [3]. Feathers made up roughly half of faecal pellet content in that same season [3].

Here is the honest limit of the method, and the authors of the 2007 paper said as much themselves: the isotopes could show that greater noctules were, seasonally, eating birds almost exclusively. They could not show whether those birds were caught in flight or picked up dead. A molecule of bird protein carries no memory of how the bird died. The paper's own language is careful on this point, presuming that the altitude at which passerines migrate allows the bats to capture, prepare and ingest them in the air, without being able to demonstrate it [3].

The Backpack That Finally Rode Along

What closes a gap like that is not a cleverer assay. It is a witness. And for an animal that flies fast, in the dark, more than a kilometre up, no human observer and no camera can be that witness. The only candidate observer that can go where the bat goes is the bat.

That is what a biologging tag is: an instrument small and light enough to ride on a wild animal without materially changing what it does, recording what the animal itself experiences. For the 2025 study, Laura Stidsholt's team fitted greater noctules at Doñana with tags built at Aarhus University that recorded movement, acceleration, altitude and sound — including the bat's own echolocation calls — on sub-second timescales [1, 9]. Picture it less as a camera and more as a flight recorder crossed with a microphone, small enough to sit like a backpack between a bat's shoulders.

The tag does not need to guess what the bat is doing. It hears the bat deciding.

Two Chases, Recorded Whole

Across the tagging effort, the team recovered two full predation attempts on tape: a chase that failed, and a chase that ended in a kill [1, 9]. Two events sounds like a thin sample, and it is — but each one is not a data point in the usual sense. Each is a continuous acoustic and inertial record of an entire hunt, seconds by second, of a kind nobody had ever obtained for this behaviour before.

The Same Trick Bats Use on Moths

To read what the tag's audio track means, it helps to know what an ordinary echolocating bat hunt sounds like, because the greater noctule did not invent a new strategy for this. Since Griffin, Webster and Michael's classic description in 1960, bat biologists have recognised a standard three-part attack sequence: a search phase, with echolocation calls spaced well apart while the bat scans open air; an approach phase, as calls quicken once a target is detected and tracked; and a terminal buzz, an extremely rapid burst of very short calls fired in the last instants before contact, giving the bat a near-continuous stream of positional updates on a target that is actively trying to escape [4, 5].

What makes the 2025 recording remarkable is not that a buzz occurred. It is what the buzz was aimed at. This exact acoustic strategy was shaped, over a very long evolutionary history, for prey a few centimetres long and a fraction of a gram, resolved at close range in an encounter that insect-hunting studies describe as characteristically brief. The tag caught the same signature turned on something that outweighs most insects a bat has ever eaten by orders of magnitude, sustained across a pursuit lasting minutes rather than an instant [1, 4, 9]. The toolkit did not change. The target did.

Twenty-One Distress Calls

The successful chase ran more than a kilometre above the ground, in total darkness, for close to three minutes [1, 9]. Somewhere near the end of it, the tag's microphone caught something no isotope assay or guano sample ever could: the bird itself, alive and audibly distressed. Twenty-one distress calls from the robin were recorded around the capture [9]. A bird does not vocalise in alarm twenty-one times over the course of being found already dead. Distress calls are what a living animal makes while something is actively trying to kill it.

This is the single fact that does the most work in the entire case. Everything before it — the feathers, the isotopes — was consistent with predation but could not exclude scavenging. A recording of the prey's own voice, mid-attack, cannot be explained by scavenging at all.

Twenty-Three Minutes of Chewing, Still Airborne

After the capture, the bat did not land, and it did not stop recording. It descended toward lower altitude and kept flying while it ate, and the tag's microphone picked up twenty-three minutes of chewing sounds as it did [9]. Add that to the roughly three-minute chase and the whole documented event, start to finish, comes to about 1,560 seconds — 26 minutes — of continuous flight, our own addition of the two reported durations, not a number either paper states outright.

A bird can be caught in under three minutes. Eating it, apparently, takes considerably longer — and the bat does not stop flying to do either.

Wings Off, Pouch Up

Handling prey that size in flight is its own engineering problem, and the recording captured how the bat solved it. According to the account of the recording, the bat bites off the bird's wings, most plausibly to cut weight and drag from a load it now has to keep aloft, and manages the remainder using its uropatagium, the membrane stretched between its hind legs and tail, pulled forward into a pouch to hold and eat the body while still airborne [9]. That pouching motion is not a new invention for this occasion. Aerial-hawking bats routinely use the same tail membrane as a scoop or basket to catch and manage insect prey mid-flight; what changed here is only the scale of what went into the pouch.

A Kilometre of Empty, Undefended Air

Both recorded hunts took place more than a kilometre above the ground, in total darkness [1, 9]. That altitude is not incidental to the story; it is close to the whole point of it. Diurnal raptors that prey on small birds hunt by sight and by day. Owls hunt largely by sound and by sight much closer to the ground and to cover. Migratory songbirds fly at altitude specifically at night, in part because it removes them from most of the predators that would otherwise be waiting. A greater noctule, hunting by echolocation in total darkness a kilometre up, is operating in a layer of night air that essentially nothing else with wings is set up to hunt in at the same time [1, 9]. Sonar does not care that there is no moon.

Why This Was Never Scavenging

Return to the question the 2007 isotope paper could not close. Isotopes describe diet; they cannot describe the manner of a prey animal's death, because the chemistry of a bird's tissue does not remember whether the bird was alive five minutes before it entered a predator's stomach. What the 2025 recording supplies instead is a continuous behavioural record spanning the entire event: a directed pursuit lasting on the order of three minutes, tracked the whole way by the bat's own echolocation and inertial sensors, ending in a capture accompanied by twenty-one distress calls from a bird that was, self-evidently, alive and resisting right up to that point [1, 9]. A carcass picked off a branch does not require a three-minute pursuit. A carcass does not scream.

Put plainly: the isotopes told the club table what the bats were eating. The tag told them how.

Half Its Own Weight, Never Landing

Asked about the size mismatch, lead author Laura Stidsholt offered a comparison worth repeating in her own terms: “A bird like that weighs about half as much as the bat itself — it would be like me catching and eating a 35-kilo animal while jogging” [9]. That is not a figure from the paper's methods section; it is the researcher's own analogy, and we are quoting it as exactly that. But the shape of the comparison is the useful part. Most flying predators that hunt on the wing take prey that is a small fraction of their own body mass, something they can subdue and carry without the encounter itself becoming a liability. A prey item at roughly half the predator's own mass, wrestled into submission and then eaten without ever landing, is a different category of feat — and it is the category the tag shows the greater noctule managing twice in the same dataset, once without success and once, at length, with it.

What Changed, and What the Two Recordings Can’t Tell Us

What twenty-four years of work changed is the type of evidence in hand: from a pile of feathers, to a chemical signature, to a continuous audio-and-movement recording of one predator killing and eating one prey animal, entirely in the air. Two recorded events is not a large sample, and the club table spent real time on that point. But the standard a single recording of this kind has to clear is not statistical; it has to demonstrate that the behaviour is physically possible and that it happened at least once under conditions a scavenger could not produce. Twenty-one distress calls mid-pursuit does that on its own.

What it cannot tell us: how often this happens across a greater noctule's whole diet and season, whether the acoustic pattern of a bird-hunting buzz differs in any measurable way from an insect-hunting one at the level of individual call timing, or whether related bird-eating bats elsewhere — a molecular diet study has already found bird remains in a similar noctule species in Japan [8] — hunt the same way. The tag answered the question it was built to answer. It also, as tags tend to, opened several it wasn't.

References

1. 1.

   Stidsholt, L., Tena, E., Foskolos, I., Nogueras, J., de la Hera, I., Sánchez-Navarro, S., García-Mudarra, J. L. & Ibáñez, C. (2025). Greater noctule bats prey on and consume passerines in flight. Science 390, 178–181. doi:10.1126/science.adr2475

2. 2.

   Ibáñez, C., Juste, J., García-Mudarra, J. L. & Agirre-Mendi, P. T. (2001). Bat predation on nocturnally migrating birds. Proceedings of the National Academy of Sciences 98, 9700–9702. doi:10.1073/pnas.171140598

3. 3.

   Popa-Lisseanu, A. G., Delgado-Huertas, A., Forero, M. G., Rodríguez, A., Arlettaz, R. & Ibáñez, C. (2007). Bats’ Conquest of a Formidable Foraging Niche: The Myriads of Nocturnally Migrating Songbirds. PLoS ONE 2, e205. doi:10.1371/journal.pone.0000205

4. 4.

   Griffin, D. R., Webster, F. A. & Michael, C. R. (1960). The echolocation of flying insects by bats. Animal Behaviour 8, 141–154. doi:10.1016/0003-3472(60)90022-1

5. 5.

   Surlykke, A. & Kalko, E. K. V. (2008). Echolocating bats cry out loud to detect their prey. PLoS ONE 3, e2036. doi:10.1371/journal.pone.0002036

6. 6.

   Popa-Lisseanu, A. G., Bontadina, F., Mora, O. & Ibáñez, C. (2008). Highly structured fission–fusion societies in an aerial-hawking, carnivorous bat. Animal Behaviour 75, 471–482. doi:10.1016/j.anbehav.2007.05.011

7. 7.

   Fortuna, M. A., Popa-Lisseanu, A. G., Ibáñez, C. & Bascompte, J. (2009). The roosting spatial network of a bird-predator bat. Ecology 90, 934–944. doi:10.1890/08-0174.1

8. 8.

   Ibáñez, C., Fukui, D., Popa-Lisseanu, A. G., Pastor-Beviá, D. & Juste, J. (2021). Molecular identification of bird species in the diet of the bird-like noctule bat in Japan. Journal of Zoology 313, 276–282. doi:10.1111/jzo.12855

9. 9.

   Phys.org (2025). How Europe’s largest bat catches and eats birds mid-air. News report on [1], including comment from L. Stidsholt.