September 2, 2009

Startled Pigeons Communicate Danger With A Whistle

Researchers have discovered that an Australian pigeon species can alert other birds of danger with a "whistle" caused by flapping its wings when the bird takes off in alarm, AFP reported.

Experts have documented the pigeon (Ocyphaps lophotes) for its well known metallic-sounding whistle that it makes when it flies from danger, but until now biologists had never analyzed the sound or explored whether it may have a use.

However, two biologists from Australian National University in Canberra recorded a crested pigeon as it tucked into grain on a feeding table. The researchers used a model accipiter hawk to startle the bird and capture the sound of it taking off in fear.

The team then compared that to a recorded takeoff of a bird as it flew unprompted from a flock, unbothered by any threat.

When the two researchers, Robert Magrath and Mae Hingee, discreetly played back the two sets of whistles to 15 groups of birds, they found that the first whistle stirred flocks to take to the skies in panic, whereas the second caused no disturbance.

The playback element of the study was revealing, according to Sue Anne Zollinger, an animal communication researcher from the University of St Andrews who was not involved in the study.

Zollinger said 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 show that the sound has a communication role.

The two whistles may seem simple and identical to the human ear, but the investigators say an acoustic analysis shows the sounds to be quite complex and distinct.

Both whistles are made up of two tonal elements and an atonal "clap". But experts say the "alarm" version of the whistle is louder and has a more rapid tempo than the "non-alarm" version "“ which the pigeons can easily tell apart.

The scientists believe that many birds have the ability to make vocal cries to alert other members of their flock, but this may be the first proof that flight noise can also serve as an alarm call.

They say the vibration of an unusually slender primary feather in the pigeon's wingtip produces the whistle, suggesting the whistle evolved not as a by-product of flight but as a warning signal to help the species survive.

The full study was published in the Proceedings of the Royal Society B, a journal of Britain's Royal Society.


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