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Namaste

Scientists have long realized that whales
communicate over vast ocean distances using
infrasound.

In recent years, researchers have discovered
that elephants also produce infrasonic calls.
The purpose of these calls is to coordinate
movements within smaller groups and larger
clans. In addition, female elephants send out
mating calls.

The elephants must convey these movement
and breeding calls over several kilometers to
reach the intended receivers. Infrasound is an
effective means for achieving this because it
has relatively large wavelengths. Infrasound
is thus less prone to scattering and attenuation
than sound in the human audible domain.

Katy Payne wrote about this research in Silent
Thunder: In the Presence of Elephants. I
enjoyed reading her book and have
summarized her landmark discoveries in the
first article.

Sincerely,

Tom Irvine
Email: tomirvine@aol.com
Feature Articles



Elephant Infrasound



Slinky Science
Welcome to
Vibrationdata
2
Elephant Infrasound by Tom Irvine




Introduction

Katy (Katharine B.) Payne is a Cornell
University Bioacoustics Research
Associate who has studied acoustic
communication and other behavior in
elephants. She wrote about her
discoveries in her book Silent Thunder: In
the Presence of Elephants, as well as in
several scientific papers.

Zoo Discoveries

Payne performed her initial research with
William Langbauer, Jr. and Elizabeth
Thomas in the Washington Park Zoo in
Portland, Oregon. They observed Asian
elephants at this zoo.

Payne listened intently to the elephants
calls. Sometimes she felt a rumbling or
throbbing that was accompanied by only a
faint sound. At other times, she felt the
throbbing but heard no sound at all.

The throbbing reminded Payne of Bachs
Passion According to St. Matthew as
played on a pipe organ.

She recalled a childhood experience:

The organist pulled out the great
stop and the air around me began to
shudder and throb. The bass notes
descended in a scale. The deeper
they went, the slower the shuddering
became. The pitch grew indistinct
and muffled, yet the shuddering got
stronger. I felt I could not hear. My
ears were approaching the lower
limit of their ability to perceive
vibrations as sound.

Note that the lower frequency limit of
human hearing is approximately 20 Hz,
although this varies between individuals.
Infrasound is considered as any sound
below 20 Hz. Earthquakes, volcanoes,
wind, thunder, and ocean storms are
natural sources of infrasound. In addition,
whales communicate via infrasound.

Payne and her colleagues borrowed some
equipment to make recordings of the zoo
elephants calls. They ran the tape
recorder at its slowest speed during
recording. They then played the tapes
back at a higher speed to raise the pitch of
the sounds. This method brought the
lowest sounds into the frequency range of
human hearing.

Carl Hopkins later analyzed these tapes at
Cornell and confirmed that they contained
infrasound.
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In addition, Payne noted that a slight
fluttering of the skin occurs between the
eyes, where the trunk meets the
elephant's head. The amplitude is about 1
cm.
Field Research in Africa
For the next research phase, Payne
traveled to Africa. She made field studies
of elephants and their calls in Kenya,
Namibia, and Zimbabwe. She performed
this work with Joyce Poole, William
Langbauer, Cynthia Moss, Russell Charif,
Rowan Martin and others.
Payne described the various types of
elephant calls as bellows, rumbles,
screams, and trumpeting. Some of these
sounds may be overtones of infrasound.
Elephants use these sounds for greetings,
warnings, distress calls, reassurance,
mating, and other purposes.
In particular, elephants use their powerful
infrasonic calls in long distance
communication. Infrasound is effective
because it has long wavelengths that
travel far with little attenuation.
The intensity of these sounds can reach
104 dB, as measured 5 m from the source.
Payne and her colleagues performed tests
in Etosha, Nambia, which showed that
elephants hear and respond to each
others loud calls from distances as great
as 4 kilometers, which is equivalent to an
area of about fifty square kilometers.
During one test, Payne and a few
associates sat on a tower that overlooked
a water hole. Two mature male
elephants, called bulls, were splashing in
the muddy overflow. The researchers at
the tower recorded the bulls behavior on a
video with a time stamp.
As part of this experiment, a van located 2
kilometers away from the water hole with a
large loudspeaker broadcast a recorded
series of a female elephants mating call.
The call was inaudible to Payne and her
colleagues at the tower, because only the
infrasonic portion could propagate over the
entire distance from the van to the tower.
The test was double-blind because
Payne and her colleagues at the tower did
not know the time at which the broadcast
would occur. Neither did they know the
location of the van.
At a particular instant, the bulls perked up.
They paused, then left the water hole and
began heading north. The elephants in
fact walked directly by the van that had
broadcast the mating call earlier. The
elephants continued their walk past the
van without stopping.
That evening, Payne and the van
operators verified that the broadcasts were
made at the exact time that the bulls
perked up and began walking toward the
distant van.
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The broadcast had been played at half-
power because the loudspeaker was
incapable of reproducing the full volume
of the female elephants call. This
allowed the researchers to extrapolate
that the bulls would have heard a full
power signal at twice the distance, which
would have been 4 kilometers.

Elephants Uses of Infrasound
Elephants use long distant infrasound for
breeding. They also use infrasound to
assemble bond groups and to coordinate
movements between groups in a clan.
A bond group is headed by a matriarch
who leads several mature female
elephants, called cows, along with their
offspring. A typical group may contain
anywhere from one to three dozen
individuals. The main purpose of the
group is the bearing, rearing, and
protection of the calves.
Bulls remain somewhat detached from
these groups but may temporarily join
them for mating.


During the day, elephants must move from
one place to another in search of food and
water. The matriarch uses calls to
assemble her group when she decides to
lead them to next location. These calls
may contain infrasound particularly if her
group has become scattered.
Furthermore, bond groups are part of a
larger clan. The elephants use infrasound
to coordinate the movements between
groups. The groups need to remain far
enough apart so that they effectively
allocate scarce food and water resources.
Sometimes this may mean that the groups
take turns at a water hole.
On the other hand, the groups need to
remain somewhat close for mutual
protection against threats, particularly lions
and poachers.
Infrasound is an effective tool for
coordinating these movements.




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Infrasound Summary
Payne and her colleagues found that
both African and Asian elephants
communicate over long distances via
infrasound. The infrasonic signals begin
at a lower frequency of 14 Hz for each
species. The infrasound has a spectrum
of energy that overlaps into the audible
range for humans. The upper limits for
Asian and African elephants are 24 Hz
and 35 Hz, respectively.
The documented distance over which the
elephants communicate during the day is
2 km, but this has been extrapolated to 4
km based on a consideration of
maximum sound power.
The calling area may be expanded by as
much as an order of magnitude during
temperature inversions in the evening
and night.
Elephants may thus communicate more
effectively during the evening, but the
risk is that lions may detect these calls.











Postscript
Paynes discoveries have proven to be a
catalyst for bioacoustic research.

Payne studied elephant infrasound as
transmitted through the air. Infrasound also
generates a corresponding seismic wave.
Stanford researchers are pursuing this
ground-borne wave.
"We have several experiments going on
right now to try to determine whether
elephants perceive seismic cues via bone
through their toenails and foot bones to
their middle ear bones, or through vibration-
detecting cells in the bottom of the foot,"
said Stanford's Caitlin O'Connell-Rodwell,
now studying the matter in Namibia.
Other researchers using Paynes methods
have discovered that rhinos and giraffes
also communicate via infrasound. This list
of animals may continue to grow.


6
Slinky Science by Tom Irvine



Introduction

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