Some people can't whistle at all, much less whistle without lips.
The walnut sphinx caterpillar has no such trouble. When disturbed, say by a predator, these North American insects compress their bodies and squeeze air out of holes in the sides of their bodies, called spiracles. The result is a shrill sound that can last for several seconds.
Now Jayne Yack, a neuroethologist at Carleton University who made the spiracle discovery, has found the high-pitched noises dissuade hungry birds.
“There are different hypotheses to explain why a predator would be deterred, and we tested the startle hypothesis: Namely, that the whistle freaks out and frightens the bird so it doesn’t come back,” says Yack, whose study appears in May in the journal Behavioural Processes.
In the laboratory experiment, when red-winged blackbirds approached a dish of tasty mealworms, they triggered a sensor that set off recorded walnut sphinx caterpillar whistles. The birds responded to the whistles by flying away, flinching, and diving—all indications the noise scared them.
While whistling helps the walnut sphinx live to see another day, the vocalisations serve many other purposes in nature. Here are five more of nature's most accomplished whistlers.
Guinea pigs make noise mostly to communicate with one another and their owners. For instance, a pup will whistle if separated from its mother.
A pair of guinea pigs pose at the Capital Humane Society in Lincoln, Nebraska. These popular pets frequently make sounds called whistles or wheeks.
PHOTOGRAPH BY JOEL SARTORE, NATIONAL GEOGRAPHIC PHOTO ARK
But pet owners may be more familiar with the other reason guinea pigs whistle: in anticipation of food. Many guinea pigs learn to identify the telltale signs of a pending meal and whistle liberally in response.
Highly social wild dogs that live in packs in the dense forests of Asia, dholes are also known as “whistling hunters.”
The dhole (above, an animal in India's Bandipur National Park) keeps in touch with its hunting companions by whistling.
PHOTOGRAPH BY FRANS LANTING, NATIONAL GEOGRAPHIC CREATIVE
Dholes hunt cooperatively, breaking into smaller groups to surround prey animals hidden deep in the vegetation. To coordinate their movements in an environment that's both noisy and visually cluttered, the canines whistle to each other.
Male mice produce ultrasonic whistles, above the range of human hearing, to court females and warn rivals of their territorial boundaries.
Recent research revealed that mice make these sounds by using their windpipes as whistles, bypassing their vocal cords altogether—a mechanism has never before been seen in an animal. In fact, it is similar to how a supersonic jet engine works.
Most marmots—found in mountainous areas in North America, Asia, and Europe—are social, using loud whistles to communicate with each other, earning many species the nickname “whistle pig.”
“Some of the marmots that live in the Pacific Northwest, like the hoary marmot, are fabulous whistlers,” says Daniel Blumstein, a biologist at the University of California, Los Angeles, who studies marmots.
Yellow-bellied marmots (pictured, an animal in Yellowstone National Park) whistle when they see predators.
PHOTOGRAPH BY, NATIONAL GEOGRAPHIC
A marmot will also whistle when it spots a predator. “Alarm calls seem to reflect urgency—how close a predator is or how scared the individual calling is,” Blumstein says.
Other marmots who hear these calls respond appropriately, looking around and scurrying to their burrows.
Every bottlenose dolphin has a signature whistle, a unique vocalisation that acts like a name. Signature whistles not only provide an identity, they help dolphins locate each other and deepen bonds.
Each bottlenose dolphin has a distinctive whistle that functions as its name.
PHOTOGRAPH BY PAUL SUTHERLAND, NATIONAL GEOGRAPHIC CREATIVE
Researchers have also shown that dolphins copy one another’s whistles to re-establish contact when separated, like a person calling her friend’s name if they lose sight of one another.
Signature whistles appear especially important for maintaining relationships between mothers and calves and between allied males.
When separated, these dolphins appear to call to their partners by copying their signature whistles—possibly a plea to be reunited.
Header Image: A male southern grasshopper mouse sings in Mexico's Chihuahua Desert. PHOTOGRAPH BY MICHAEL & PATRICIA FOGDEN, MINDEN PICTURES, NATIONAL GEOGRAPHIC CREATIVE