ByJason Bittel
Published February 14, 2024
Outside an abandoned mine in British Columbia, Canada, the sounds of love are in the air—though you’ll need to tap into ultrasound to enjoy them.
Bats are famous for producing sounds that help them orient themselves in the night sky and zero in on insects to munch upon. These are known as echolocation.
But in the winter of 2010, audio recording devices known as bat detectors picked up a new kind of noise, one which had never been recorded for silver-haired bats before.
“We started seeing this pattern of sounds that really couldn’t be echolocation, because they produced it so quickly, the bats didn’t have time to listen for the echoes,” says Cori Lausen, a research biologist and director of bat conservation for Wildlife Conservation Society Canada. “And it was this very patterned sound, and it was almost every night.”
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Lausen describes the pattern as being composed of a lead call, followed by a droplet call, and finishing with a series of multiple chirp calls. While the sounds are of such high frequency that they can’t be heard by human ears, by time-expanding each song, Lausen has brought the silver-haired bat’s songs into the range of human hearing. (The findings were published in the journal Wildlife Society Bulletin in December 2023.)
About the weight of six playing cards, silver-haired bats are one of the most common bat species in the forests of Canada and the United States.
While it’s unclear which sex is producing the refrains, Lausen says that research conducted in other bat species, as well as physical evidence that the bats were mating at the time of the recordings, suggests the songs are used for courtship.
Bat love songs, in other words.
What’s more, the findings could usher in a new era of understanding about mating behavior among North American bats, with many more bat songs just waiting to be discovered.
What is a song?
From the cricket’s chirp to the bullfrog’s bellow, you might think that nature is awash in music. But not every noise found in the natural world is considered a ballad.
“The difference between a call and a song is kind of important,” says Mike Smotherman, a biologist specializing in auditory neuroscience at Texas A&M University. “Frogs have a call, and they just repeat it all the time, but we don’t really call that a song.”
Much more rare are the animals that layer different syllables, each with their own meanings, into the sounds they produce. Humans and birds are the most well-known examples of animals that create this kind of complexity.
(These lemurs also sing in a rhythm previously only found in humans and birds.)
Many species of bats do produce audible sounds, Lausen says. “If you've ever had a colony of bats in a bat-box or in your attic, for example, you'll sometimes hear them making little squeaky chirp sounds.”
As for singing? Numerous species in Europe have been known to belt it out, but until now, only one species in North America has joined them—the Mexican free-tailed bat.
Smotherman, who studies that species, says the males’ songs contain one set of syllables intended to attract females, while each song closes with an aggressive buzz meant to repel other males. At the same time, other elements may allow the bats to differentiate themselves from the sounds produced by other bat species.
“So I think I see all of that in what they recorded in the silver-haired bats,” says Smotherman, who was not involved in the new study. “They’re definitely what I would call songs.”
A love song for bats
While this is probably the first time many people will be hearing about bat songs, it very likely will not be the last.
“In the last 20 years, we’ve had this new technology emerge that lets scientists go out in the field and record the songs and document who’s making them and what the context is,” says Smotherman. “I expect that we’re going to see an explosion of these kinds of observations, and it’s really going to change the way people think about bats.”
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Aside from being a fascinating addition to the scientific literature, Lausen says the songs could potentially help scientists map new areas where silver-haired bats live, as well as to determine whether such areas are appropriate for wind energy projects. Wind turbines are known to kill migratory bats in unsustainable numbers, she says.
As fate would have it, all that time spent researching how bats find their beaus may have led to another pairing.
Years ago, before bat safety protocols changed, it was routine for scientists to warm up bats they’d sampled before releasing them back into the wild. The best way to do so was to put them on your skin, like a newborn baby. And human armpits are particularly effective bat incubators, it turns out.
Lausen clearly remembers the moment she watched another graduate student she’d never taken much notice in before offer his armpit to a bat in need.
“He’s now my husband,” she laughs.
