Late last year, I wrote about a bird called the rocket-tailed drongo and, in response to a comment, I noted the following:
“Drongos are notorious thieves and mimics. In South Africa, I spent a morning with a meerkat researcher, following live meerkats. He said that he had anecdotal evidence that the fork-tailed drongo would sometimes mimic the predator alarm calls of meerkats while they were foraging and then swoop down to nick their unearthed morsels.”
Well that evidence is no longer anecdotal. In a new study published today, Tom Flower from the University of Cambridge has indeed found that fork-trailed drongos can deceive meerkats into scurrying for cover by making false alarm calls. It’s the bird that cries hawk.
Drongos are great opportunists. The fork-tailed species will follow meerkats as they forage, taking beak-sized morsels that they dig up or flush out, and even occasionally stealing prey from the meerkats themselves. They’re also excellent mimics and some researchers have noted that they can accurately imitate the calls of other species. Flower wanted to see if they use these deceptive skills on the meerkats they follow.
He spent eleven months in South Africa’s Kalahari Desert tracking a wild group of 50 fork-tailed drongos that had been given individually coloured rings. Flower’s observations revealed the extent of the drongos’ thievery. They spent around 1% of their time following meerkats, and around a quarter tracking another small bird, the pied babbler. The food they stole from these species accounted for around a quarter of their total calories. And half of these thefts involved a false alarm that fooled the target into seeking cover from a non-existent threat.
The drongos use a combination of alarms. Some are their own, but others are imitations of the warning calls of glossy starlings, crowned plovers and pied babblers. Foraging animals often form watchful alliances, where different species recognise and listen out for each others’ alarms. If one spots danger, the entire alliance runs for cover.
For now, it’s unclear if they can imitate meerkat calls. “I do have recordings of drongos mimicking what I think are the alarm calls of meerkats,” says Flower. “They appear similar structurally and sound similar but I have not yet analysed these to prove that they are definitely meerkat alarm call mimics. This work will be published in the future once the analyses are done.”
By analysing the different drongo calls, Flower showed that the fake ones are indistinguishable from their genuine counterparts. Their targets think so too; when Flower recorded the drongo calls and played them back to the meerkats and babblers, he found that they were just as likely to abandon their food in response to the true and false alarms (but not to random drongo calls).
The young drongos probably pick up the skill by watching adults. Juveniles will often follow adults on their robbery missions and they make false alarms for themselves after they see their mentors doing the same.
Several species fake their own alarm calls to scare their peers away from food but Flower says that this is the first study to conclusively show that one species can mimic the alarms of another for the same purpose. Admittedly, the idea isn’t new – it just hasn’t been subject to this level of rigorous testing. For example, way back in 1986, Charles Munn suggested that two birds – the white-winged shrike-tanager and the bluish-slate antshrike – do the same thing. Others have since suggested that the birds are simply shouting aggressively, but Flower’s study shows that this clearly isn’t true for the fork-tailed drongos.
It might seem strange for the meerkats and babblers to be so consistently duped by the drongo, but their behaviour makes sense. If they react to a false alarm, they lose a meal but if they ignore a true alarm, they lose their lives. Their gullible streak ensures their survival.
However, you would expect the drongo’s mimicry to eventually start wearing thin. If it makes too many false alarms, its targets might eventually learn that they are being duped (and indeed, the drongos lie about danger around three times as often as they tell the truth). The babblers seem to have started down this road – they largely ignore false versions of the drongo’s own alarm call. The drongo, however, is versatile enough to switch calls if one becomes ineffective and indeed, the mimicked cry of a panicked starling will still send the babblers into flight.
Reference: Proc Roy Soc B http://dx.doi.org/10.1098/rspb.2010.1932
More on mimicry:
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