Dolphins
and porpoises make two kinds of sounds:
- one that sounds like a whistle
- a clicking noise
You can hear them at the Marine Mammals Acoustics page here.
The animals use the whistle-like sounds to communicate.
The clicking sounds are used to "echolocate." That's like sonar (used
by submarines). Dolphins and porpoises send out the clicks into the water
and the clicks bounce back off the objects around them. By "reading" the
clicks that are bounced back, the dolphins and porpoises can identify
what's around them and where! This is how they hunt for fish and navigate.
Scientists still don't agree on exactly how it works. But here's what
many think.
How do they make the clicks?
Scientists think the sounds are created just below the animals' blowhole,
in their nasal passages. (Humans use their vocal chords to make sounds,
but dolphins and porpoises don't have vocal chords.)
The
sound is sent to the front of their heads to an organ called the MELON!
(So you can call your new friend a melon-head and not get in trouble!)
The melon is filled with an oily substance which focuses or directs the
sound forward, in a sort of beam.
How do they receive the clicks that are bounced back at them?
Scientists think the echoed sounds or vibrations are received by the animals'
lower jaw, and then passed to the middle ear and brain for processing.
So they "talk" with their nose and forehead, and "hear" with their jaws!
Fishies Beware!
The clicks sent out by dolphins and porpoises help them to hunt for food
by showing them where it is. But many researchers believe the clicks are
also used as a weapon! The sounds may temporarily stun nearby fish, making
them easy prey.
Danger from Humans?
If dolphins' and porpoises' navigation systems are disturbed or hurt,
it can kill them. If they lose their way, they can get trapped in a shallow
area and end up washed ashore. They can't get back to the water by themselves,
and if they're not quickly rescued, will die of dehydration.
Many people believe that the increasing use of "Low Frequency Active Sonar"
(LFAS) for military use is causing dolphins and porpoises around the world
to lose their way and die. You can read more about this at the Stop LFAS web site. Others disagree. You can read their
side at the U.S. Navy's web site here.
We're giving you both these links so you can read both sides of the argument
and make up your own minds. CBC4Kids isn't responsible for the content
of external sites, and we can't necessarily endorse what they say.
Links:
U.S. Navy's
LFAS web site
Stop LFAS web site