Masters of the art of deception

Aesop’s fable, about the boy who cried wolf, warns children that too many lies told too often, will result in nobody taking you seriously. However, the fork-tailed drongo has found a way of breaking the rules of deception by using remarkable feats of vocal mimicry.

With its glossy black feathers, hooked beak, red eyes, and a forked-tail, the drongo is a devilish-looking bird renowned for alarming others, and even attacking predators many times its own size, including the formidable martial eagle. It has the reputation of being the neighbourhood watchdog among small ground-foraging birds and mammals.

They eavesdrop on the drongo, as well as one another’s alarm calls to detect potential danger. However, when following these other species while they forage, the drongo often turns their alarms to a more Machiavellian purpose. When they spot an individual unearthing a particularly enticing food item, the drongo raises the alarm, causing everyone to dash to cover, while it swoops down to pilfer the abandoned food.

Drongos are known to deceive more than 25 other species using these false alarms, including weavers, babblers, hornbills and even meerkats. Nevertheless, their victims soon wise up to the drongos’ deceitful ways and start ignoring their false alarm calls. Then, drongos have another trick – they can also mimic the alarms of the species they target. When they spot an opportunity to steal food from a meerkat for example, they mimic the meerkat’s alarm calls. If target species latch onto this trick, drongos switch their alarm calls again, mimicking the alarm call of a different species. While drongos can mimic the alarm calls of over 40 species, this is not unique.

This fascinating behaviour is especially common among the songbirds, 20% of which are vocal mimics. Possibly the most accomplished vocal mimic, the lyrebird, can copy the calls of countless other species, and even mimics the noise made by chainsaws and camera shutters, sounds that are apparently common in their native forest habitats of Papua-New Guinea and Queensland. Despite the prevalence of vocal mimicry, scientists still puzzle over why it is done. One explanation is that male birds incorporate mimicry into their song to make themselves more attractive to females. Alternatively, call mimicry might be used to deter competing species from a territory, by deceptively signalling that it’s already occupied.

Another popular explanation is that by mimicking the calls of predators, species might deceive and deter other predators. If attacked by a hawk, they mimic a more threatening species such as a martial eagle! For the fork-tailed drongo the reason is clear. They use alarm-call mimicry to steal food. Our confirmation of this was recently published in the journal, Science. To collect the evidence, drongos were followed on foot for five to 15km a day, six days a week for six months annually from 2008 to 2013, across the red dunes of the Kalahari Desert close to the Kgalagadi Transfrontier Park.

Questions still remain around how drongos learn to mimic other species’ alarm calls, and how they are able to adapt their false alarm calls to deceive other animals. This apparently “clever” trick suggests that drongos intentionally manipulate the minds of other animals just as humans might when we try to pull off the same trick. However, drongos might instead accomplish such complex behaviour by completely different means, by using simple trial-and-error learning to hone their tactics. Robotic models, from which drongos can steal food using false alarms, are now being used to work out just how they perform this fascinating behaviour.