New research has found that the 6 gram brown thornbill mimics the hawk alarm calls of neighbouring species to scare a nest predator by convincing it that a much bigger and scarier predator – the brown goshawk – is on its way.
Currawongs, which raid the nests and hunt the chicks of thornbills, are also prey to goshawks. Although currawongs normally benefit from listening in on hawk alarm calls of other species, thornbills exploit this and turn it against them.
As well as issuing their own hawk alarm call, thornbills mimic those of the local species to create the impression of an impending hawk attack, which in turn distracts the pied currawong – a predator 40 times larger than the thornbill – providing thornbill nestlings with an opportunity to escape.
While animals often mimic dangerous or toxic species to deter predators, the thornbill is a surprising example of a species mimicking another harmless species to trick a predator.
The research, conducted by scientists at the University of Cambridge and the Australian National University (ANU), is published today in the journal Proceedings of the Royal Society B.
“The enormous size difference between a tiny thornbill and a 0.5kg goshawk might make it difficult for thornbills to mimic hawk vocalisations accurately, limiting them to mimicking the chorus of hawk alarm calls given by small local species instead,” said Jessica McLachlan, a PhD student from Cambridge’s Department of Zoology, who co-authored the study.
“As hawks are silent when hunting, the alarm calls of local species may be the only sound that warns of a hawk’s presence,” she said.