The startled pigeons produce a whistling alarm call with their wings
Startled pigeons might not appear to epitomise the wonder of evolution, but a study has discovered that the birds can communicate with their wings.
When a crested pigeon is startled into flight its wings produce a whistling sound which serves as an alarm call.
The pigeons have "modified wings" that produce the whistle as they fly, but only this sudden take-off creates the alarm that causes other birds to flee.
The team report their findings in the Royal Society journal Proceedings B.
Robert Magrath at the Australian National University (ANU) in Canberra led the study.
He and his colleague Mae Hingee took sound recordings from the birds.
"We audio recorded the sound of birds flying off from a feeder in routine flight and compared those sounds to those produced when we scared pigeons into take-off with a gliding model hawk," explained Dr Magrath.
The birds that took off in alarm produced louder whistles with a more rapid tempo of "notes", he told BBC News.
The researchers played back both alarmed and routine whistles to flocks of feeding pigeons.
"We found that they only fled to cover after hearing the alarmed whistles. [They] could tell the difference, and acted appropriately in response," said Dr Magrath.
He described how the birds' "modified" wings create the sound.
"The birds have one very narrow primary flight feather, which we suspect vibrates during flapping flight to produce the whistling," he said.
The pigeons have "modified" wings that produce the whistling sound
Sue Anne Zollinger, an animal communication researcher from the University of St Andrews who was not involved in the study, said the "playback" element of the study was revealing.
"Lots of people have studied sound production by birds' wings, but here the researchers have actually been able to put it into a context, [and] shown that the sound has a communication role," Dr Zollinger told BBC News.
She added that this information would help researchers to understand why being in a flock might be useful for some birds.
The ANU researchers pointed out that while scientists understand some evolutionary advantages of a flock, such as having more pairs of eyes to spot predators, this has clarified exactly how the birds understand that one of their flock has spotted a potential threat.
Dr Magrath concluded: "We'd like to find out more about the mechanism of sound production, try to work out whether it evolved specifically as an alarm signal, and see if other birds also use wing sounds [as alarm calls]."
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