When in a tight corner, it can be really useful to lie through your teeth. Humans are experts at using our voices to deceive, as anyone who's been on the wrong end of a scamming sales call will know. But animals do it too.
Some creatures sound a false alarm to scare off the competition, effectively crying wolf. The males of some species can mimic the call of a fearful predator in order to scare a female – who might freeze in fear long enough to allow the male an opportunity to mate with her. And some animals can even call out in a way that makes them sound like they taste bad.
Here are four kinds of animal that have turned verbal deception into an art form.
Moths broadcast their lies
They aren't exactly famous for their vocal skills, but some moths do produce sounds. A few species are prolific percussionists.
The moth advertises its distastefulness with an easily recognizable clicking signal
Tiger moths produce sound using tiny blisters of cuticle called tymbal organs on the left and right sides of their thorax. Their technique is similar to squeezing an empty aluminium can. "If you squeeze it, it clicks," says William Conner of Wake Forest University in Winston-Salem, North Carolina. "When you release it, it makes a second click." Each tymbal has many ridges, so they can fire off 4500 clicks per second.
Sometimes these sounds are used as honest warning signals. For instance, an adult delicate cycnia moth tastes bad, because as a caterpillar it ate plants imbued with toxins, and stored these chemicals in its body. The moth advertises its distastefulness with an easily recognizable clicking signal. Hungry bats quickly learn to avoid moths broadcasting these sounds.
But other moths, which taste perfectly fine, can deviously mimic the delicate cycnia's warning clicks.
The polka-dot wasp moth is one such mimic, and Conner has shown that its lying ways pay off.
He tethered delicate cycnia moths on a string, and released naïve bats that had been raised in a lab and so had never met the noxious moths. Over five nights, the bats learned to avoid them.
Then on night six, he replaced the delicate cycnia moths with polka-dot wasp moths. Only one of the test bats was brave enough to nab it. To check that it was the clicking sounds that were scaring off the bats, Conner removed the moths' tymbals, and found that bats had no qualms about gobbling up the tasty moths.
"Lots of other nocturnal insects probably also make sounds," says Conner's colleague Jesse Barber. "It's likely that there are these massive acoustic mimicry complexes in the night sky."
But it's not just about avoiding being eaten. Some sneaky moths, like males of the Asian corn borer, can imitate bat sounds as a means to get lucky with the ladies. These dastardly male moths make bat-like sounds to make females freeze in fear, then take the opportunity to mate with her.
Last year Ryo Nakano, now at the University of Toronto in Canada, and his colleagues, found that female corn borer moths could not distinguish between the sound of a real bat and the sound of a male moth imitating a bat. Asian corn borer males "are not good at copulation," says Nakano, so they use this trick to improve their odds.
Nakano has also found that male yellow peach moths use a similar sonic hoax to disrupt the approach of rivals when in hot pursuit of a female.
Bats be jamming
Bats have their own sonic tricks up their sleeve. Many navigate by echolocation, sending out pulses of ultrasonic sound and listening for them to bounce back from objects. As a result, they are vulnerable to dirty tricks by some of the moths they are attempting to grab. That dirty trick is called jamming – a siren-like noise given at close range – that messes up the bats' ability to interpret its echolocation signals.
We kept hearing this funny signal that the bats were making
Jamming of bat signals by moths has been known for some time, but recently, while studying Mexican free-tailed bats, Conner and Aaron Corcoran discovered that it wasn't just moths doing the jamming.
While videotaping moths jamming bats, "we kept hearing this funny signal that the bats were making," says Conner. This signal turned out to be a method of competitive jamming: bats foiling other bats as a way to snatch each other's food.
"Imagine two bats approaching a target," says Conner. "The one in the front is just about ready to catch the target moth. The one in the back sends out the jamming signal. It jams the guy in the front, and the guy in the front misses [the target], and then the guy in the back comes in and cleans up." It's the first time this has been documented in animals.
It's unclear how jamming works. One idea is that jamming signals create a "phantom echo" that sends the recipient in the wrong direction. However, biologists now think jamming is not really a deceptive signal, but a way to block signals from being interpreted correctly.
Monkeys that lie for bananas
In Aesop's fable of The Boy Who Cried Wolf, a shepherd boy pranks his neighbours with false alarms. He gets his comeuppance when a real wolf appears and no one believes his cries for help. However, in nature some animals win out by raising false alarms.
The capuchins are completely insane for bananas
Tufted capuchin monkeys are masters of false alarms. Brandon Wheeler of the University of Kent in Canterbury, UK has shown that they use deceptive alarm calls to grab extra food.
Working in Iguazú National Park in Argentina, Wheeler's team was studying how the capuchins respond to predators, using experimental feeding platforms strung up in the treetops. The platforms were stocked with bananas, which the capuchins "are completely insane for", says Wheeler.
He saw that the highest ranking capuchins would "just sit there and eat as much as they want, and subordinate individuals just sit on the outside watching them." Occasionally the junior monkeys tried to reach in for a piece, but when they did, the senior capuchins often bullied them.
But something odd was going on. Capuchins make hiccup-like alarm calls to warn of an approaching wild cat, and Wheeler heard these calls much more often at the feeding platforms than elsewhere. Wheeler suspected that the junior capuchins were crying wolf to scare their elders away from the bananas.
In a series of experiments, Wheeler found that it was almost always the low ranking individuals that were giving the false alarm calls. What's more, they used the fake calls more when the food was clumped on just one or two platforms. "When you've got more platforms, even the low ranking individuals don't need to deceive their way in to get access," says Wheeler.
It works because the threat of predators is very real
The senior capuchins are not deceived for long, so it's a snatch and grab operation for the deceiver. "It's not like the individual who gives the call gets the rest of the bananas," says Wheeler. "It gives it a chance, at best, to run in and grab three, four or five banana pieces, and run out."
It works because the threat of predators is very real. "The cost to receivers of ignoring honest alarm calls is too high," says Wheeler. The price of ignoring a genuine warning may be death, so they may accept being duped occasionally.
Duping by dastardly drongos
African birds called fork-tailed drongos run a food-stealing racket similar to the capuchins'. In the dry savanna of the southern Kalahari, Tom Flower of the University of Cape Town and his colleagues have studied what they get up to.
Individual drongos hang out with lots of other bird species in mixed-species flocks. In those flocks, the drongos are security guards. They warn everyone within hearing distance about approaching predators, allowing the other birds to flee.
Drongos can mimic the warning sounds of about 45 other species
Thanks to the drongos, birds like southern pied babblers and other animals like dwarf mongooses can spend less time standing guard and, at least in the case of the babblers, more time stuffing their faces with food.
But fork-tailed drongos also use false alarm calls to steal food, by scaring their competitors out of the way. Earlier this year, Flower reported that drongos can mimic the warning sounds of about 45 other species, including the bark of a meerkat.
This sounds like bad news for the other animals, but the drongos may be a good thing overall. In another recent study, Flower and his team looked at how one of the most common species in the flocks, the sociable weaver, responds to the drongos.
It seemed the weavers preferred to have the drongos around
Sociable weavers build massive communal nests that house between 20 and 500 individuals. They normally feed within 1.5 km of this home base. Flower's team followed foraging flocks of weavers and observed their feeding habits. By recording drongo calls in the presence or absence of weavers, Flower discovered that the drongos have a special call that they only use when weavers are around.
Perhaps surprisingly, the weavers were attracted to these sentinel calls. They seemed to be an "all clear" signal, calling the weavers back if they had scarpered – including on occasions when the alarm call had been a fake. It seemed the weavers preferred to have the drongos around. When they did, the weavers spent more time foraging and less time standing guard.
It seems the sociable weavers put up with the manipulative drongos, even though they use sneaky tricks to steal food, because they also prevent others from being eaten. And the arrangement with the multi-species flock clearly works for the drongos. They obtain nearly a quarter of their total food intake by crying wolf.