Liar, Liar, Wings on Fire: This Clever Desert Bird Survives Through Trickery
Once, in the southern African nation of Botswana, I watched a troop of baboons make their way blindly through an overgrown field. The tops of their heads barely cleared the tall grass, like the helmets of a military patrol walking into an ambush. They were oblivious of the presence of a cheetah cutting across at an angle to intersect them. I held my breath in anticipation. Then, suddenly, a bird—a little spoilsport hornbill—put out an alarm call. Heads popped up, and the parties veered off in opposite directions.
The idea that animals listen in on the alarm calls of other species is not new. Birds, mammals, and lizards do it, and some species can even respond appropriately, depending on whether another species is warning of an eagle or a snake. But a study out today in the journal Science shows a big leap forward in this remarkable behavior with an account of the astonishingly complex “tactical deception” practiced by the fork-tailed drongo.
Drongos are a common bird species across sub-Saharan Africa. They’re glossy black and about the size of an American robin. They have a reputation for being fearless and will readily run off raptors many times their size. “If they see an eagle, they zoom right up in the air at it like a surface-to-air missile and latch on to the tail,” says Tom P. Flower, a behavioral ecologist at the University of Cape Town and lead author of the new study.
Drongos prey mainly on insects, often hawking them out of midair—for instance, around outdoor electric lights. But they are also kleptoparasites: That is, they steal food that other species have located or caught. It’s a common way of living in the natural world, and lions, hyenas, jackals, and, of course, vultures also do it—but none with the artfulness and audacity of the fork-tailed drongo.
In the Kalahari Desert, a drongo will frequently travel in a mixed pack with southern pied babblers. They also associate with meerkats. These other species benefit, according to the study by Flower and his coauthors, because drongos produce honest warning signals at any hint of an approaching predator. So having a drongo perched high up on a bush nearby means the babblers and the meerkats down on the ground can spend less time being vigilant and more time feeding.
But their watchdog drongo also lies. Because he has a history of saving lives with his honest warnings, his false alarm calls also make the babblers and meerkats scatter—for just long enough for the drongo to swoop in and steal their food.
You might think that this would only work for a little while. We all know from the legend of the boy who cried wolf that telling the same lie over and over just makes everyone ignore you, even if you mix it up with the occasional truth. So in addition to their own alarm calls, drongos have learned to mimic the alarm calls of no fewer than 45 other species. They collect this spectacular repertoire mainly from other local birds, and, of course, from the babblers and meerkats.
Drongos are by no means the only successful vocal mimics in the animal world, nor even the only ones to use mimicry as a means of deception. Burrowing owls in the American West, for instance, imitate rattlesnakes to discourage potential predators from entering their nesting holes. But the drongos deploy their mimicry with an unparalleled degree of tactical variation. For example, babblers predictably become just a little skeptical of drongo alarm calls, and they will resume foraging more quickly than they do after the alarm call of a different species. The drongos produce mimicked calls 42 percent of the time, according to Flower. The babblers also get skeptical when they hear the same type of alarm call three times in a row. So when a drongo is making repeated food theft attempts on the same target, it uses a different alarm call three times out of four.
The remarkable thing is that the drongos go to all this trouble to get just 23 percent of their daily diet. But Flower points out that this is no small advantage in an environment as harsh and resource-poor as the Kalahari, particularly in winter. It may seem as if the drongos have taken this game to such an inventive extreme at least partly for their own amusement. But the more likely reality is that becoming a clever thief is a matter of survival.