In the classic story, a boy tries to repeatedly fool his town into believing that there is a wolf on the prowl. This morality tale ends poorly for the boy, but a small Australian bird can do one better. When a pied currawong goes looking for brown thornbill nestlings to eat, the thornbill parents call wolf—or, actually, they call hawk. The false alarms fool the currawong into thinking that its own predator, the brown goshawk, is nearby. The tiny thornbill thus effectively outsmarts its large enemy.
To explore how this sophisticated ruse works, biologist Branislav Igic, then at the Australian National University, and his colleagues positioned a taxidermied currawong near thornbill nests while broadcasting nestling distress calls. The thornbills sounded their hawk alarm calls and even mimicked the alarms of other species. Igic also tested 18 currawongs by broadcasting the sounds of the thornbills' mimetic and nonmimetic hawk calls. He found that the playback discouraged the currawongs from hunting. The results were published this past spring in the Proceedings of the Royal Society B.
The researchers think that alarm calls from what sounds like multiple callers might make the warning seem more reliable. “Birds can adapt some very interesting and unique strategies to protect their young,” says Igic, who is now at the University of Akron. The thornbills' own hawk calls fooled the currawongs for 8.3 seconds on average, but when Igic included the mimicked calls, too, the currawongs were distracted twice as long. That padding may provide enough time for the nestlings to escape the nest.
Visual mimicry, exemplified by harmless king snakes that resemble venomous coral snakes, is well known to animal behaviorists, but vocal mimicry has remained more mysterious. “This is further evidence of the benefits some vocal mimics gain from their unusual vocal behavior,” says University of Cape Town ornithologist Tom Flower, who was not involved in this study. He ultimately would like to see proof that deception actually increases nestling survival. For now, unlike the fabled townspeople, the currawongs have yet to catch on to the thornbills' lies.