- Squirrels have been recorded using high-pitched ultrasonic
"whispers" that are inaudible to the human ear but warn each
other of danger.
-
- It is the first time that any animal has been found to
use ultrasound for an alarm call although high-frequency sounds well beyond
the range of human hearing are widely used by bats.
-
- The discovery that squirrels communicate using ultrasound
was made by James Hare, professor of zoology at the University of Manitoba
in Canada, and his student David Wilson.
-
- They were studying the audible alarm calls of the Richardson's
ground squirrel, a social animal that lives in burrows of closely related
females and their offspring. This species of squirrel - sometimes called
a gopher - lives on the prairies of North America and has developed a sophisticated
communication system to warn of approaching predators.
-
- Professor Hare noticed a female opening its mouth as
if in alarm and emitting faint sounds of rushing air, an apparently noiseless
whisper which nevertheless triggered a vigilant posture in her nearby relatives.
-
- "I thought initially that she had lost her voice.
Then I noticed other squirrels doing the same so I decided to use a bat
detector which can record ultrasound," Professor Hare said.
-
- "Sure enough, we found that the whisper call was
actually full of ultrasonic frequencies and this was directed at other
squirrels nearby," he said.
-
- In their study, published today in the journal Nature,
the two scientists say that ultrasonic frequencies produce highly directional
sound that can help a squirrel disguise its presence from a predator yet
still warn other squirrels.
-
- "To our knowledge, ultrasonic alarm calls have not
previously been detected in any animal group, despite their twin advantages
of being highly directional and inaudible to key predators," they
write.
-
- Recordings of individual squirrels making a "whisper
call" were replayed to other members of the group. The results clearly
indicated that the squirrels used ultrasonic frequencies to communicate.
-
- "It was found that the animals spent significantly
more of their time on vigilant behaviour in response to the whisper calls
and audible control than in response to background noise," the scientists
say.
-
- The squirrels studied by the scientists used both audible
calls and whisper calls when they saw a potential threat. "Audible
calls evoked a more pronounced response than whisper calls, suggesting
that whisper calls either convey less urgency than audible calls or that
respondents react less conspicuously," they say.
-
- Professor Hare said that ultrasound communication may
be more common among animals than previously imagined.
-
- SOUND INSTINCTS
-
- Bats: Echo-location is a form of sonar that bats use
to move around and capture prey in the dark. They emit ultrasonic squeaks
from their mouths which bounce off nearby objects
-
- Whales: Very low frequency sound of long wavelengths
- the opposite to ultrasound - carry for enormous distances underwater
and are used by some whales in long-distance communication. The killer
whale however uses ultrasonic clicks to communicate over short distances
-
- Honey bees: When honey bees find a rich source of nectar
they can communicate the direction and distance it is from the hive by
performing a dance in the shape of a figure "8" which takes into
account the height of the Sun and the angle of flight needed to be taken
from the hive
-
- Birds: Song is a ubiquitious feature of birds and the
dawn chorus is believed to result from individuals needing to stake out
a territorial claim each morning.
-
- © 2004 Independent Digital (UK) Ltd http://news.independent.co.uk/world/science_technology/story.jsp?story=545776
|
