Thornbill scares off predator by mimicking hawk warning

By Karl Gruber 5 June 2015
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A tiny Australian bird scares off predators by imitating a warning call for a bigger predator

WHEN THE TINY brown thornbill (Acanthiza pusilla) feels threatened by the pied currawong, at almost 40 times its size, it starts singing – but not just any song, according to new research. The thornbill tweets a call used by other birds to warn that a hawk is lurking nearby, tricking the currawong into thinking a bigger predator is about. And the ruse works.

“The brown thornbill tricks the currawong not by mimicking the calls made by the hawk, but by mimicking the hawk warning calls of local species,” says lead researcher Dr Branislav Igic, who conducted the study whild he was at the Australian National University but is now at the University of Akron, In Ohio, USA. “Hawk warning calls are probably better in this trickery because hunting hawks rarely call, and the only sounds indicating that there’s one nearby are the warning calls of local species.”

While previous research has documented birds imitating other species’ calls or even eavesdropping another bird’s call, this is the first study to demonstrate that birds can imitate another species call to fool a predator, the authors say.

Bird mimic trick works to fool predators

The findings happened by pure chance, while researchers were performing other experiments on thornbill behaviour, says Dr Robert Magrath, senior author of the study.

“I was puzzled because I could hear the alarm calls of robins, honeyeaters and rosellas, but I couldn’t see any,” he said. “I soon realised that the brown thornbill was mimicking the other species, and Branislav later discovered they sometimes lie about the type of predator present when defending their nests,” he said.

In their experiments, researchers used a fake currawong to test the reaction of brown thornbills when their nest was threatened. Thornbill parents started singing, imitating warning calls from between one and four different species. (You can hear some of their calls here).

Researchers then recorded the thornbill’s fake warning calls and played them back to currawongs. The big birds were scared, searching the sky for hawks for about 16 seconds, says Magrath, long enough to allow a weary thornbill to escape or seek cover.

Using another bird’s warning call works better than the thornbill’s own hawk warning call, which only distracted the currawongs for half as long.

“The results really surprised me; I never imagined that the thornbill’s vocalisations could work so effectively in fooling currawongs,” he adds.

Branislav plans to study if this behaviour is present in other thornbill species. “Other species of thornbill are also speculated mimics and could potentially use similar strategies to defend their nests,” he says.

The research was published this week in the Proceedings of the Royal Society B