Crested pigeon's wings act as an alarm

Scientists have discovered the purpose behind the crested pigeon's unique whistling wings.
By Tobi Gerdes | Nov 13, 2017
Researchers have finally uncovered how and why crested pigeon's wings whistle when they take flight.

The unique birds -- which live throughout most of mainland Australia -- are characterized by the loud noise they make when they take to the air. In fact, the sound is so distinct that many know the species as "whistle-winged pigeons."

Scientists have long known about the strange sound, but they have not known its purpose until now.

In the recent study, a group of scientists led by researchers at Australian National University discovered that the whistling wings function as an alarm that warns other pigeons of nearby danger. They first investigated the idea because they believed the sounds could be a elusive, non-vocal form of communication,Gizmodoreports.

To test that theory, the researchers took high-speed videos of crested pigeons taking flight and paired the footage with acoustic recordings.That showed the noise changed between a high note in the wing's downstroke, and a low note during the upstroke. Not only that, but they also discovered that the pigeon'seighth primary (P8) flight feather is roughly half the width of the feathers on either side of it.

To see if that strange feather caused the whistling, the team removed certain feathers and noted how they affected the pigeon's sound. This revealed that birds without their P8 feathers made whistles with completely different high notes than ones who had them. As a result, it is likely the P8 feathers modify the sound as the birds fly.

Next, the scientists tested the birds to see if the whistles happened with each wingbeat. They examined them under different types of flight -- categorized as normal, casual, and escape -- and found that escape flights had faster wingbeats and created high-tempo whistling, where normal flight produced a different sound.

Finally, the researchers tested to see pigeons responded to the alarm by exposing them to recordings of escape flights. They found that pigeons typically did not move when they heard the whistle from pigeons that had their P8 feathers removed. However, they did react and scatter when they heard sounds from normal birds. That shows the noise does indeed signal danger.

"We show that the crested pigeon produces an acoustic alarm signal with its wings and that it is an intrinsically reliable signal of danger," said lead author Trevor Murray, a researcher at The Australian National University, according to Phys.org."The alarm signal is intrinsically reliable because pigeons flap faster to escape predators, and this fast flapping automatically produces the high-tempo alarm signal."

The discovery is interesting because this anatomy is not found in any other bird species. While some birds are able to make sounds with their winds, the crested pigeon's whistle is unique because it shows both the production and response to a signal. This is a true sign of non-vocal communication, and the team hopes to further study the properties to see what it can tell them about avian evolution.

The results are detailed in the journalCurrent Biology.

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