Charles Darwin once posited that birds might flap their wings to communicate, not just to fly. However, this has always been pretty tricky to test. Now, 150 years later, researchers have discovered that crested pigeons use their wing feathers to warn others of impending doom.
Crested pigeons live in Australia and are known for their interesting hairstyles and the noise they make when they fly. From the latter, they have earned the nickname “whistle-winged pigeons”. But whether this sound serves a purpose, or is just a side-effect of flight, has always been unclear.
Now, it turns out that these birds use a very narrow and specific wing feather – the eighth primary one to be exact – to produce distinct notes with each downstroke. As the pigeons flap faster, such as when escaping danger, the tempo of these notes increases.
Along with these high notes, the researchers found that the ninth primary wing feathers of the birds create contrasting low notes. However, only the high notes are important in sounding an alarm.
"Crested pigeons signal danger with noisy wings, not voices," lead author Trevor Murray, of The Australian National University, said in a statement. "It shows that birds really can use their feathers as 'musical instruments' to communicate with others."
The study, published in Current Biology, also showed that when other pigeons hear the high tempo flapping sounds, they flee. Meanwhile, when a group of pigeons heard the wing flapping of a bird that had had its eighth primary wing feather removed, they just looked about rather than taking flight.
Being a pigeon certainly has its risks. You have to deal with cats, dogs, bigger birds, and small children running at you. Having an alarm system that is basically an automatic result of escaping seems like a pretty good idea.
"The alarm signal is intrinsically reliable because pigeons flap faster to escape predators, and this fast flapping automatically produces the high-tempo alarm signal," Murray explained.
What’s more, it’s not just crested pigeons that are noisy fliers. All sorts of other birds, from hummingbirds and manakins to other types of pigeons, do not have subtle takeoffs, so the researchers think that further research might unveil more about the evolution and use of wing sounds in this unique group of animals.
"Birds have such prominent voices, we have largely ignored their surprisingly complex instrumental sounds,” said Robert Magrath, also from the Australian National University.
So, next time you’re in the park and hear the pigeons making a racket, the sound might actually be a little more complex than it first seems.