The more we learn about cetacean acoustics, the more they continue to astound us with their vocal abilities! Here is a run-down of acoustical info on various cetacean species:
The
Mysticetes:
- Blue
Whales: non-vocal, extremely low frequency,
~40Hz, 10-15 seconds long
- Fin
Whales: (the
earth shakers),
lowest frequency of all whales, ~20Hz,
sounds were first detected by geologists
on seismographs (that's a deep rumble!!).
Both blue and fin whales are pelagic breeders
and therefore need long, deep calls to
locate each other in an environment filled
with ambient noise.
- Humpback
Whales: 20-800 Hz, very loud, sing
songs on breeding grounds (learn more below!).
- Right
Whales: call types have been correlated
to behaviours, different calls for swimming,
socializing, sexual activity etc.
The
Odontocetes:
- Tursiops (the
bottlenose dolphin): the most acoustically
studied marine mammal, mostly in captivity.
Large range of frequencies (7-15 kHz) in
clicks and whistles; high discriminatory
ability. Use signature whistles to identify
themselves (like a name) and communicate
with group.
- Sperm
Whales: called the Carpenters
of the Sea because
their clicks sound like hammers tapping
incessantly. They click almost continuously
to orient themselves. Their codas are
collections of 5-10 clicks repeated in
a pattern. They use codas to identify groups
of whales and individuals and keep track
of each other over long distances.
- Beluga
Whales: The Canaries
of the Arctic,
so called because of their impressive acoustic
range, from 1.5 kHz and 60 kHz. In the
face of high ambient noise levels, the
Hawaii population of belugas shifted their
frequency levels from 40-60 kHz to 100-120
kHz. They shifted their signals to a frequency
band where the ambient noise was reduced.
- Killer
Whales: broad use of frequencies (4-18
kHz), both clicks and pulsed calls; it
has been recognized that they subpopulations
of killer whales communicate in group specific
dialects (learn more below!)
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WAIT!!
What about animals other than whales?!!?
Yes!
Although
research on ocean acoustics has primarily been
focussed on large cetaceans, there are many
other animals in the ocean that create sound
besides whales! The pinnipeds are quite vocal
too! Seals and sea lions emit underwater growls,
grunts and roars. Male walruses have pharyngeal
(throat) pouches that are filled with air.
When they dive they make gong-like sounds by
striking their pouches. The walrus performs
elaborate courting displays using sound. And
fish can make a lot of noise, gulping, chirping,
tapping and booming with their swim bladders.
Snapping shrimp make a typical cacophony in
the backdrop of any ocean sound scape. They
sound like rustling leaves or Rice Krispies
popping!
So you see, the ocean is truly alive with sound!
Read on to learn about some particularly accomplished
acoustical animals:
Song
of the Humpback
Killer
Whale Dialects
Weddell
Seal: Sounds out of this World
The Song of the Humpback
Humpback whales (Megaptera novaeangliae) are the most musical of the mysticete whales. The songs of the humpback were first detected by military arrays in the 60’s. And when scientists dropped their hydrophones into the waters of the breeding grounds, they were instantly intrigued by the deep, haunting sounds of the whales. And indeed, humpbacks truly do sing songs.
The
sounds they make are organized into themes, repeated
consecutive phrases of music. Individual phrases
of the song are usually only last a few seconds and
under 1.5 kHz in frequency. The sounds include long
groans, low moans, roaring sounds, trills, and chirps.
Each song lasts anywhere from 8-16 minutes and the
whale may sing for hours on end, repeated the song
over and over again. All the whales that share a
breeding area sing the same song. That means that
the whales in the North Pacific sing a different
song than the whales in the North Atlantic. The songs
also evolve over time. Individual phrases are dropped,
new ones inserted or the sequence of themes is altered
slightly. Over time (many years), an entirely new
song will come about. How do the changes occur? Scientists
do not understand the process completely but believe
that it may be forgetfulness or innovation. Then,
other whales actively learn from each other, and
the changes are passed on through the group (kind
like the game "Telephone").
Why
do they sing?
Underwater observations of humpbacks have determined that it is
only the males that sing. Likewise, the songs are only heard on
the breeding grounds. This leads biologists to think the songs
are a kind of breeding behaviour. Perhaps the songs are a way to
attract females or to mark their territory. It is thought that
the way the male sing indicates to a female that he will be a good
mate. Although all the males are singing the same song, they are
not synchronized. There is random overlap with small variations.
Perhaps the whale with the most novel song is a dominant whale.
What is most fascinating about the songs of the humpback is that
we still do not know HOW they do it. Whales do not have vocal cords
and the long, deep and musical sounds of the humpbacks leave whale
biologists mystified. It is most likely that the sounds are produced
somewhere in the nasal passages (similar to echolocation sound
production), but the process is not fully understood. So, as research
continues, the song of the humpback continues to haunt us.
 Click
here to listen to the humpback song!
(a link to Dr. John Ford's web site at UBC)
Killer
Whale Dialects
The killer
whales (Orcinus orca) of the North Pacific
are the most well studied whales on earth. Field
observations of these whale populations have been
ongoing in British Columbia, Washington and Alaska
for more than 20 years.
In the last 10 years, much
of this research has been focussed on killer whale
communication, and the results have been extremely
interesting. The killer whales on the Pacific Coast
communicate in group-specific dialects.
The
East Pacific population of killer whales is divided
into three ecotypes:
- Residents:
are piscivores (fish eaters), and remain in
localized areas (they are further divided in
the Northern and Southern Residents.
- Transients:
are mammal- eaters and have unpredictable movements
- Offshores:
feed on schooling fish and remain offshore,
not well studied.
Although
these ecotypes can be differentiated based on
morphology, feeding behavior and genetics, they
also have different call repertoires. Because
transients feed on animals (like dolphins and
porpoises) that have sonar abilities too, they
are generally fairly silent, so as not to alert
their prey to their presence. Only after a kill,
will transients become quite vocal. Residents
on the other hand are quite a chatty bunch of
whales! When whale biologists in British Columbia
drop a hydrophone into the waters surrounding
Vancouver Island, judging from the sounds they
hear they could tell you whether it is a southern
or a northern resident, what clan and even what
pod the whale belongs to. A pod is a group of
whales in the same matriline (i.e.: they have
a common grandmother or great-grandmother). Each
pod has a repertoire of 7-17 discrete calls,
distinct to that pod. Often the whales will have
calls in common with other pods in their clan
( a clan being pods that have similar dialects
and a common ancestor). Recently it has been
determined that the dialects of killer whales
reflect their genetic relationships. In other
words, the more similar the dialect, the closer
the whales are related.
Functions
of the dialects:
Combined field observations and genetic analysis suggest that
the dialects serve to identify groups of whales. They may help
coordinate pod movements and maintain the integrity of the pod.
It is also thought that the dialects prevent a whale from breeding
with others that are too genetically similar. By breeding with
an animal with a sufficiently different dialect, a killer whale
is ensuring genetic mixing.
Click
here to listen to different killer whale dialects!
(a link to Dr. John Ford's web site at UBC)
The
Weddell Seal:
Sounds Out of this World
The Weddell Seal (Leptonychotes weddell) stands out among the pinnipeds as the most outrageously vocal. The booming calls, whistles, chirps, buzzes and trills of this seal sound like sound effects out of Star Wars! Scientists working in the Antarctic have classified 12 distinct Weddell call types with frequencies ranging from 0.1 kHz to over 70 kHz (well outside the range of human hearing). So, what are they trying to say with all this racket? Most of the calls are related to breeding behaviour. Calls are used for mate attraction, asserting dominance and for defending a territory around a breathing hole. During the breeding season, researchers have recorded up to 20 calls per minute! However, the rest of the year, the seals remain quiet to listen for the sounds of killer whales or leopard seals (their main predators). You have to hear these outlandish sounds for yourself to believe they are made by a living animal!!
Listen at these links:
Underwater Field Guide to Ross Island & McMurdo Sound, Antarctica
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