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Bats · echolocation

Bats aren't blind, but they hunt by ear. Find the moth by its echo

A small bat, like the ones that circle street lamps in summer, finds a moth in the dark by the echo of its own call. The echo comes back in about a hundredth of a second. Slowed 10 times, you can hear it. Then you hunt.

Put on headphones: in them you also hear which side the echo comes from. Sound starts only when you press. On an iPhone, take the phone off silent.

You are the bat. Somewhere ahead of you is a moth

A common pipistrelle (Pipistrellus pipistrellus) calls about 10–12 times a second while it searches for food. The call here is synthesised from measurements. Press and listen to one call at its real speed. You won't hear a thing, and that is the first surprise.

In short: the bat calls, the sound reaches the moth and comes back; from the echo's delay, the bat knows how far away its prey is.

What you actually heard

Most of a common pipistrelle's call sits around 45 kilohertz, and human hearing stops at about 20. And it is no faint call: some tropical bats hunting in open air reach 122–134 decibels, measured 10 centimetres from the mouth. For us, it is silence. The call lasts about 6 milliseconds.

To bring it into your hearing, you slow it down, as researchers do with their recordings. Slowed 10 times, the call drops to 4.5–5.6 kilohertz and lasts about a tenth of a second. The echo arrives the same way, slowed too.

1.1–2.2 mthe distance at which a common pipistrelle notices an insect, measured in the wild
6.6–12.8 msthe echo's round trip over those distances
343 m/sthe speed of sound in air at 20 °C

The sum is the one you just did by ear: sound travels to the moth and back, so the distance is the time multiplied by the speed of sound, divided by two. At 2.2 metres, the echo returns after 12.8 milliseconds. The bat gets an echo like this for every call, dozens of times a second, on the wing.

A whole attack takes less than a second

When it hunts, a bat calls faster and faster. First it searches, with a call every 85–95 milliseconds. Once it has an echo, it closes in with shorter, more frequent calls. Over the last 50 centimetres it starts a buzz: up to 180–200 calls a second. The whole pursuit, from approach to catching the insect, usually lasts 0.2–0.55 seconds.

  • search
  • approach
  • final buzz

Press to hear the attack.

The attack here is a schematic built from values measured on wild common pipistrelles, not one recording: 34 calls in 774 milliseconds: three searching, then a 519-millisecond pursuit ending in the 160-millisecond buzz of 24 calls. Bat detectors divide the frequency without slowing time; this is how the night sounds to the people who count bats.

A moth hears the bat from 30 metres

Many moths have ears. In a common European moth (Noctua pronuba), researchers measured the hearing neuron: it responds to the call of Leisler's bat (Nyctalus leisleri) from up to 33.2 metres. The bat only notices the moth at 8.7–15.4 metres. The moth knows first, and has time to dodge.

One bat found a way round it: the barbastelle (Barbastella barbastellus) calls in a whisper. Measured 10 centimetres from the mouth, its call is 94 decibels, against 127 for Leisler's bat. The moth's neuron responds to it only from under 3.5 metres, while the barbastelle notices the moth at 2.2–5 metres, often farther than the moth can hear it.

And yet it sees

"Blind as a bat" is a saying, not biology. Most bat species have working eyes, with cones, and many have kept their sensitivity to ultraviolet. A flower-feeding bat of tropical America (Glossophaga soricina) sees ultraviolet light down to 310 nanometres.

For hunting small insects, eyes matter little. Sight helped the northern bat (Eptesicus nilssonii) only with moths with a wingspan of at least 5 centimetres, which it spotted from 3.5 metres on average. For a tiny insect in the dark, there is the echo. Old World fruit bats (Africa, Asia, Australia) lack the larynx-made echolocation of other bats (a few echolocate with tongue clicks); they rely more on sight.

A thousand mosquitoes an hour? Nobody measured that

The figure has circulated for decades. It seems to come from an experiment by Donald Griffin and colleagues, published in 1960: bats kept in a small room full of insects, set loose for 10–15 minutes. The best result with mosquitoes was 9.5 a minute, for 15 minutes, by a 3.7-gram bat. With fruit flies the rate reached 20 a minute.

Multiply by 60 and you get 600 or 1,200 "an hour". But the paper gives no hourly figure, and the wild has no room full of mosquitoes. A small North American bat (Myotis lucifugus) eats, by field measurements, between 1.8 and 3.7 grams of insects a night, many midges and other small flies, but also beetles and moths, not just mosquitoes.

In Romania: 32 species, all protected

The Carpathian Bat Research Center counts 32 species in Romania. All are protected by law. The species you listened to is the common pipistrelle: 3–8 grams, with a wingspan of 20–23.5 centimetres.

If you find a grounded bat, don't touch it with bare hands: it can carry viruses related to rabies, and a bite can be so small you don't notice it. Wear thick gloves or call a specialist. If you were bitten or scratched, wash the wound well and see a doctor.

In winter, bats hibernate in caves, attics and cellars. A bat reserve in western Poland, Nietoperek, closes to visitors from 15 October to 15 April, while they sleep. Every waking costs them: arousals during winter can use 60–85% of the energy of the whole hibernation. A visitor who disturbs a bat can wake it and leave it short of the reserves it needs to reach spring.

Tonight

Common pipistrelles leave their roosts about 20 minutes after sunset (a figure measured in Britain). Stand by a street lamp or above still water and watch for their broken, zigzag flight. Some of those sudden turns are attacks: a buzz you cannot hear, over in less than a second.

How we made this

All sounds are synthesised in your browser from published values, not recorded. The call: 6 milliseconds, a falling sweep followed by a nearly constant tail at 45 kHz (Kalko and Schnitzler, 1993). Slowing it 10 times divides the frequencies by 10 and multiplies the durations by 10. In the game the moth sits at 1.1–2.2 metres, the detection distance measured on wild common pipistrelles (Kalko, 1995). Echo loudness and headphone direction are approximate: your ear uses the same cues as the bat, but less finely. The attack is a schematic: the intervals are those measured for search, approach and buzz, not those of one pass; the schematic's pursuit lasts 519 milliseconds, inside the measured range.

Sources

  1. Kalko E.K.V., Schnitzler H.-U. (1993). Plasticity in echolocation signals of European pipistrelle bats in search flight. Behavioral Ecology and Sociobiology 33: 415–428. doi:10.1007/BF00170257
  2. Kalko E.K.V. (1995). Insect pursuit, prey capture and echolocation in pipistrelle bats. Animal Behaviour 50: 861–880. doi:10.1016/0003-3472(95)80090-5
  3. 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
  4. Elemans C.P.H. et al. (2011). Superfast muscles set maximum call rate in echolocating bats. Science 333: 1885–1888. doi:10.1126/science.1207309
  5. Goerlitz H.R. et al. (2010). An aerial-hawking bat uses stealth echolocation to counter moth hearing. Current Biology 20: 1568–1572. doi:10.1016/j.cub.2010.07.046
  6. 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
  7. Simões B.F. et al. (2019). As blind as a bat? Opsin phylogenetics illuminates the evolution of color vision in bats. Molecular Biology and Evolution 36: 54–68. doi:10.1093/molbev/msy192
  8. Liu Z. et al. (2022). Molecular convergence and transgenic evidence suggest a single origin of laryngeal echolocation in bats. iScience 25: 104114. doi:10.1016/j.isci.2022.104114
  9. Winter Y., López J., von Helversen O. (2003). Ultraviolet vision in a bat. Nature 425: 612–614. doi:10.1038/nature01971
  10. Müller B. et al. (2009). Bat eyes have ultraviolet-sensitive cone photoreceptors. PLoS ONE 4: e6390. doi:10.1371/journal.pone.0006390
  11. Rydell J., Eklöf J. (2003). Vision complements echolocation in an aerial-hawking bat. Naturwissenschaften 90: 481–483. doi:10.1007/s00114-003-0464-x
  12. Anthony E.L.P., Kunz T.H. (1977). Feeding strategies of the little brown bat, Myotis lucifugus, in southern New Hampshire. Ecology 58: 775–786. doi:10.2307/1936213
  13. Carpathian Bat Research Center, Bats of Romania; Romania's national report to EUROBATS (2026), PDF.
  14. Bat Conservation Trust, Common pipistrelle (weight, wingspan, frequency, emergence after sunset).
  15. Villada-Cadavid T. et al. (2025), Oecologia, doi:10.1007/s00442-025-05835-9; Borzęcka J. et al. (2021), Biology 10: 593, doi:10.3390/biology10070593.
  16. CDC, Rabies and bats.