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."
Mute-swan touchdown near Slimbridge, Goucestershire, England. Photo courtesy
of Adrian Pingstone and Wikipedia.
"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 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 may have been whooper swans, migrating to
breeding grounds in Scandinavia or Siberia. These 5-feet (1.5 m) long,
20-pound (10 kg) big birds fly laboriously but cruise at 50 mph (75 km/h). 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. 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."
 Courting
mute swans. Photo courtesy of Bowenpan and Wikipedia.
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, hear their calls, Cornell University
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, 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 2, 2007)
|
|
|
