These Small, Stealthy Bats Use High-Frequency Vocalizations to Keep Their Chatter Out of the Range of Predators and Prey

New research shows that proboscis bats communicate with each other and echolocate at higher frequencies than scientists expected. This could help the animals sneak up to their targets and evade creatures that want to eat them

Katie Cottingham | Freelance Writer

September 23, 2026 9:00 a.m.

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The tiny proboscis bat sits outside on tree trunks during the day and eats insects like moths and mosquitoes, keeping the bug population in check. But settling out in the open is a dangerous lifestyle that leaves these bats—which are even smaller than an adult house mouse—at risk of being eaten by the large birds and spiders in the rainforests of Central and South America.

“As a bat, if you choose to roost outside, you need to make sure you’re not detected,” says behavioral ecologist Lena Dressler, a researcher at Berlin’s Natural History Museum. Brown speckled wings and fur that blend in with tree bark allow proboscis bats to hide in plain sight, for example. “But you also want to make sure you’re not eaten when you want to communicate,” she adds.

A study that Dressler and colleagues published in July in the Annals of the New York Academy of Sciences now shows that not only do proboscis bats demonstrate visual camouflage, but they also hide vocally. They echolocate and communicate at very high frequencies, so prey can’t hear them approaching until it’s too late and predators often don’t notice them.

Timing is everything

Mirjam Knörnschild, a behavioral ecologist and evolutionary ethologist who runs the laboratory where Dressler works at Berlin’s Natural History Museum, wasn’t impressed with proboscis bats when she first observed them. “I was convinced for pretty much a decade that bioacoustically, they were the most boring guys ever,” says Knörnschild, co-lead scientist of the study at the Natural History Museum, Humboldt University of Berlin and the Smithsonian Tropical Research Institute in Panama.

The problem was that Knörnschild had initially observed them at the “wrong” time of year—the summer months. When the team realized that the bats actually vocalize a lot, especially during mating season, which is a few months in spring and again in fall, they wanted to find out everything they could about proboscis bat communication.

So, Dressler and behavioral ecologist Martina Nagy, co-lead scientist and postdoctoral fellow at the Natural History Museum, flew to Costa Rica. Both researchers observed and recorded the vocal repertoire of free-ranging proboscis bats in Guanacaste. Nagy conducted additional studies at the La Selva field station, established by the Organization for Tropical Studies. Hanging out with bats was not always easy. The researchers had to stay very still, and unwanted visitors would stop by. “On one occasion, monkeys were throwing mangoes at my equipment, so I had to leave,” says Dressler.

Chatty batty

In the study, the team found that proboscis bats vocalize with at least 22 distinct types of syllables, defined as the smallest unit of a sound surrounded by silence. A syllable that the bats frequently used is called a “hook” because it decreases in frequency at the end, giving it a hook-like shape on a spectrogram. The bats produced some syllables once, as a monosyllabic vocalization, but they also produced the same syllable multiple times in a series. Additionally, the bats made complex vocalizations, combining different syllables.

Overall, the team recorded 17 different vocalizations, or combinations of syllables. Some of the few vocalizations that humans can hear are called “songs,” which males produce during mating season. These songs are complex and the longest vocalization the researchers recorded.

The team’s data suggests that one hook series out of the range of human hearing—documented with an ultrasound microphone and recorder—may communicate social information, such as the identity of the bat and its sex. The bats make hook vocalizations to communicate while attempting to stay hidden, like when they are rocking, or swaying with wind gusts to disguise their grooming and other self-care activities.

Most predators of the proboscis bat cannot hear sounds above 40 kilohertz, and the bats make only a few syllable types below that frequency. Humans can only hear up to about 20 kilohertz. These naturally selected sounds also do not travel far. These characteristics suggest that proboscis bats are using naturally selected high-frequency vocalizations as a form of camouflage, or what scientists call crypsis, to hide from animals that might try to eat them.

“Many social signals appear adapted to remain relatively inconspicuous, whereas sexually selected signals such as song, which may need to reach other bats flying nearby or even neighboring colonies, are much more conspicuous,” says Nagy. “This nicely illustrates that there is not one optimal way to communicate—the properties of a signal depend on what the animal needs it to accomplish.”

High-frequency hunters

Bats use echolocation, a kind of bio-sonar, to navigate and hunt prey. To get an idea of how proboscis bat echolocation calls compare with those made by closely related species, the team constructed a phylogenetic tree of its relatives in the emballonurid bat family. The researchers examined the relationship between echolocation call frequency and body size across these species. Smaller bats usually emit higher frequencies, so the researchers figured that the proboscis bat calls would be high—but they were exceptionally high, even when taking body size into account.

Digging deeper, the researchers calculated the distance at which a moth could hear an approaching proboscis bat. For the bats, “detection occurs only at very short distances, less than about [nine feet] in our calculations, so bat and moth may detect each other almost simultaneously, leaving the moth little time to escape,” says Nagy. “Closely related bats calling at lower frequencies can be detected considerably earlier. This pattern is exactly what we would expect if acoustic crypsis contributes to the unusually high call frequencies.” The higher frequencies could also help the bats detect small prey better, suggesting that acoustic crypsis may be one of several selective advantages of these calls, she notes.

Because the echolocation calls are at very high frequencies and travel short distances, they could help the bats avoid detection by both prey and predators. “The idea that these calls are cryptic against predators is novel and intriguing,” says Marc Holderied, a sensory ecologist and bioacoustician at the University of Bristol in England, who was not involved in the project. “The study is a treasure trove of discoveries.”

According to the study data, echolocation calls and hook vocalizations share many features. “This finding made us wonder if hooks also help the bats perceive the environment similar to the echolocation call, but in a modified way,” says Dressler. The two types of sounds may have evolved together. “Echolocation and social calls share the same sound-production and hearing systems, so selection on one may have influenced the other,” Nagy says.

Looking ahead

Proboscis bats are common now in Central and South America, but Knörnschild worries that they may not weather climate change, or the super El Niño that will peak later this year. “Panama and Costa Rica basically didn’t have a rainy season, and all the models are saying that it’s not going to rain until next April,” says Knörnschild. “That’s about a full year without rain in what is supposed to be one of the wettest places on Earth.” She adds that when the last super El Niño hit in 2015, many greater sac-winged bats that they had observed for a different study—about 60 percent of the adults and almost all of the juveniles—were lost.

In the meantime, the team is trying to learn as much information as they can about these bats. Dressler is now focusing on the songs. “We want to know how the song is composed, who’s singing, when and why,” she says.

Holderied suggests looking at other aspects of the vocalizations. “The researchers haven’t measured the amplitudes of these bats’ calls,” he says. He explains that measuring amplitudes could uncover even more diversity in the bats’ vocalizations, but it is not an easy experiment. “To get amplitudes, you need to know the location of the sound source, which is difficult in flight.”

Now that Knörnschild knows much more about proboscis bat vocalizations, she has a new appreciation for the little critters. “I really do think they are one of the most remarkable species I’ve had the privilege of working with in my career,” she says. “They are amazing and very special.”

Katie Cottingham  is a writer covering biology, medicine, chemistry and materials science. Her work has been featured in Scientific American, Science, Chemical & Engineering News, INFORM, EpiGenie and more.