SATURDAY, 3 MAY 2014I was going to start by writing about my research on the cooperative behaviour of meerkats in the Kalahari desert - but heck, you can read about that here. Instead: some new findings published yesterday in Science about another inhabitant of the Kalahari Meerkat Project: the fork-tailed drongo.
Drongos, which are common throughout Southern Africa, are one of the few bird species to be seen with regularity in the harsh environment of the arid desert. As a meerkat researcher, I've spent many hours in the company of these birds, which spend an inordinate amount of time perched near meerkat groups. Dr Tom Flower, who kicked off his academic career as a project manager at the Meerkat Project, had noticed this too - and the relationship between drongos, meerkats, and other bird species, became the focus of his PhD at Cambridge.
Over the course of his doctorate, Tom habituated a large population of drongos to his close presence, enabling him to give them each identifiable leg ring combinations (see pic below), and observe closely their foraging behaviour. His subsequent research showed something exciting - that drongos weren't just hanging out with meerkats and other species for good company (sometimes including MY company). By employing sneaky tactics and good timing, drongos were making alarm calls just when a target animal found a juicy food item, causing it to leap to safety, and giving the drongo an easy meal. Why don't meerkats and other species ignore these crafty calls? Because drongos also make true alarm calls when a real predator is approaching - and meerkats, often the snack of birds of prey like martial eagles, can't afford to take any chances.
This all so far fits well with the central tenet of zoological research - that natural selection likes jerks. If you already reckon that you wouldn't trust a drongo with your lunch money, you haven't heard the half of it. Tom and his colleagues have discovered that drongos have a "vocabulary" far beyond what we'd imagine - and in his new paper they show that they are able to put their wide repertoires to good use to get what they want. Tom has recorded a total of 51 different alarm call types in his drongo population, with each bird having a range of between 9 and 32 calls that they use regularly. Here's the amazing part: only six of those calls are drongo-specific alarm calls. The rest are mimics of their target species' alarm calls - including meerkats, and another habituated species at the Meerkat Project, the pied babbler (a cooperatively breeding bird).
Tom and his co-authors Matt Gribble and Amanda Ridley were able to show, using experiments in which alarm calls of different types were played back to pied babblers, that when drongos made alarm calls that sounded like the alarm calls of the species they were targeting, their target animals took longer to return to foraging. In other words, pied babblers generally reacted to drongo alarm calls, but REALLY flipped when a drongo alarm call sounded like a babbler alarm call.
They also showed that, in a sequence of 3 alarm calls, when the alarm call stayed of the same type, the response of pied babblers decreased - they were cottoning on to the deception. However, when the last call switched to another type of alarm call, the response level remained high. Ever heard of the boy who cried wolf? Drongos prevent babblers and another target species, the pied babbler, from learning to be sceptical of their alarm calls by switching it up.
Using field observations of drongos with a target animal, they found that this tactic really does work in natural circumstances. When drongos failed to get the target to drop their food and run with one type of alarm call, they were more likely to change the type of false alarm call and have another go. When they made this kind of change, they were more likely to successfully steal the target's food.
Tom, who moved from Cambridge to take up a postdoc at the University of Cape Town, told ScienceMag that drongos at the very least seem to have an understanding of cause and effect, hinting at greater cognitive abilities than might have previously been attributed to this common little bird. Their ability to manipulate and exploit other animals in their ecosystem makes them one of the Kalahari's great survivors. “They’re all eavesdropping on each other", he says. "It’s like they speak each other’s language.”
You can watch the fork-tailed drongo in action, narrated by the silky smooth voice of Sir David Attenborough, here.