The brown thornbill, one of Australia’s tiniest birds, is 40 times smaller than its predator: the pied currawong. Should be easy picking, right? Not exactly. The humble-looking bird is able to outwit the predator by mimicking the warning calls of bigger, more terrifying birds. The study, published in the journal Proceedings of the Royal Society B, is the first to show that vocal mimicry can be used by birds to scare predators.
The currawong usually preys on the thornbill’s nest and in a fight, the currawong would easily win. Currawongs are vigilant birds that listen out for any hawk alarm calls—particularly from their predator, the brown goshawk—to stay alert for any incoming danger. The thornbill cleverly exploits this by mimicking the alarm calls of other birds, creating the impression of a looming hawk attack. While the currawong is distracted by the thornbill's deceit, the offspring in the nest are given a chance to escape.
"It's not superbly accurate mimicry, but it's enough to fool the predator," says Dr. Branislav Igic of the Australian National University, who carried out the study, in a statement. "I am amazed that such a tiny bird can mimic so many species, some much bigger than itself. It's very cunning.”
Researchers actually came across the thornbills’ mimicry by accident. They weren’t sure why they kept hearing the warning calls of a variety of birds when studying the birds’ reaction to a stuffed owl.
"I was puzzled because I could hear the alarm calls of robins, honeyeaters and rosellas, but I couldn't see any," Professor Robert Magrath, who led the research group, said in a statement. "I soon realized that the brown thornbill was mimicking the other species, and Branislav later discovered that they sometimes lie about the type of predator present when defending their nests."
To study the effect of the mimicry, researchers filled fake thornbill nests with chicken pieces and observed how currawongs reacted to different calls. The currawongs became distracted for 16 seconds when the thornbill's trick calls were heard. Researchers suggest this would be enough time for the nestlings to flee. When the currawongs heard the thornbill's own call, it was distracted for only half a second.