The ability to produce and perceive sound is important for whales – to navigate, find food, and communicate.
Toothed whales can use echolocation to hunt their prey. They send out high frequency clicks then listen for their echo as they bounce back from objects – like the next meal!
Baleen whales use low frequency sound to communicate, sometimes over considerable distances. Recent research suggests that they do this with their larynx – the ‘voice box’ in land mammals. Some baleen whales, such as male humpbacks, produce extremely complex ‘songs’.
‘Seeing’ with sound
One of the most startling adaptations of toothed whales is echolocation.
Echolocating whales, such as sperm whales, send out a series of clicks, then interpret the echoes these make when they bounce back from objects. This bio-sonar locates prey with great accuracy and provides a way for these whales to ‘view’ their world.
How does sound travel through water?
Sound travels as vibrations through matter. In fact, sound travels four times faster through the denser medium of water than through air!
Experiments with dolphins show that they can use echolocation to detect a small object at some distance. They can distinguish its shape and what it’s made of. They can also look at an object with their eyes, then identify it again using only echolocation.
Echolocation means these whales are not dependent on light. They can hunt even in the darkness of the deep – as with sperm whales seeking out giant squid.
Human sonar devices work in exactly the same way, although the whale’s bio-sonar is far more sensitive and subtle.
How a dolphin produces and receives sound
Dolphins have monkey lips!
Air is forced through a pair of flaps made of fat and gristle that have been dubbed ‘monkey lips’. These vibrating lips create the initial sound.
Use your melon!
As the lips vibrate, the sound is transmitted via the whale’s ‘melon’ – fatty tissue that makes up its forehead. This tissue has the same acoustic properties as water. The sound, therefore, passes into the sea with minimal loss of energy. Toothed whales can direct sound by bouncing it off air sacs in their nose and possibly by using face muscles to alter the shape of the melon.
Dolphins have the ability to make two sounds at once. Each nasal tube has its own set of lips that can vibrate independently, possibly a thousand times a second.
Listening with fat!
The echoes that return from the sound pulses are received by a deposit of fat in the dolphin’s jaw. This ‘acoustic fat’ relays the sound along a thin channel of fat to the dolphin’s ear bones.
How a sperm whale produces and receives sound
At least a quarter of a sperm whale’s length is dedicated to its nose – a third in mature bull sperm whales. This giant nose is actually an elaborate sound-generating device.
A sperm whale’s blowhole is on the front left side of its head. This is the animal’s left nasal passage. The right nasal passage has no exterior opening. Instead, it supplies air to the ‘monkey lips’ for sound production.
The monkey lips vibrate and the sounds they make bounce off an air sac. They then pass through the waxy, liquid contents of the spermaceti organ and are reflected off an air sac behind it.
The sounds pulse through several lenses of fat – whalers called them ‘the junk’ – which focus the sounds into a narrow beam. This beam of sound emerges from the front of the head, and sperm whales can direct it – like a searchlight used to sharply illuminate a target.
The sperm whale receives the sound much like the dolphin – through a large pad of fat in the rear of the jaw. This, in turn, is relayed along a fine channel of fat to the ear bones.