A Swan Mystery

Q: Recently we were sitting outside and heard a bizarre noise coming from something flying over our heads. We realized it was a couple of swans, and we are now trying to figure out what the noise was.
Some of us suggested it was a sort of singing or signaling, others that it was their wings making the noise. Can you help us out? We have a dinner at stake!
Mimi, Copenhagen, Denmark

A: The swans that flew over you were probably mute swans, which ornithologist Philippe Jourde of the Service Etude du Patrimoine Naturel in France says "is the most common swan in that part of Europe."

"When flying, their wing beats produce loud, penetrating, rhythmic singing sounds — resembling 'vaou-vaou-vaou...", and audible one to two kilometers (a mile) away," emails Jourde. The loud wing sounds may help the birds stay in touch with one another, especially during migratory flights.

Moreover, contrary to their name, "mute swans are not mute," says Jourde. According to the Birds of Western Palearctic: calls are "often hoarse, explosively snorting, snoring, or grunting, usually with little of crooning, trumpeting, or honking quality of more vocal Cygnus [swans]." You can hear their calls (www.birds.cornell.edu/AllAboutBirds) by clicking here. Unfortunately, I couldn't find a recording of their wing beats, but are these calls the sound you heard?

On the other hand, they might have been whooper swans, migrating to breeding grounds in Scandinavia or Siberia. Or perhaps they were the smaller Bewick swans, heading for Siberia.

It's hard to say which of these three swan species flew over, but whoopers are certainly the noisiest. Birders liken whoopers' calls to a sound like 'gang-go-gang-go' or 'hoo-hoo-hoo.' Human imitation, though, does not come close. Only a recording begins to capture the bugle-like trills (http://www.oiseaux.net/oiseaux/anseriformes/whooper.swan.html). Is this the sound you heard?

You no doubt also heard their wings beating. Whooper-swan "wings produce a musical sound when flying," say French ornithologists of the Oiseaux.net (meaning 'birds'). Moreover, their varied, modulated song sounds like a "husky, distant bell."

By the way, whoopers sing while courting, and mate for life. They dance with their necks to the tune of "loud bursts of trumpeting," says Birds of Britain. A pair faces each other with lifted, quivering wings, half open. Each bends the long, thin neck into a graceful curve, heads almost touching, then lifts and straightens the neck, in time with the other, and repeats the movement many times.

Let us know who won the bet!

Further Reading (and Listening):

Whooper Swan best audio, interesting info,Oiseaux.net

Mute swan, Animal diversity web, University of Michigan

Whooper Swan Migration, USGS

The Birds of the Western Palearctic, Robert Gillmor et al

Whooper Swan good audio, www.whatBird.com

Bewick's Swan, good audio, RSPB

Whooper flight speeds, National Environmental Research Institute, Denmark, Netherlands Institute of Ecology

Readers' answers to Question of the Month:

It depends on the type of swan. There's a species called the Trumpeter Swan with good reason. Based on your location, you might have heard the Whooper Swan. Both vocalize, unlike the also aptly-but-not-very-imaginatively-named Mute Swan.
- Melissa T., Dayton, Nevada, USA

I own a home on a lake where there are many swans. The noise you heard is the flapping of their wings as they fly. Since they are very big, they work very hard to stay aloft.
- Richard, Port Washington, New York, USA

Maybe it was their "swan song."
- Carol, Crawford, Texas, USA

(Answered July 9, 2007)