Cetacea: Encyclopedia II - Cetacea - Breathing Seeing Hearing and Echolocation

Cetacea - Breathing Seeing Hearing and Echolocation

Since the cetacean is a mammal, it needs air to breathe. Because of this, it needs to come to the water's surface to exhale its carbon dioxide and inhale a fresh supply of oxygen. Naturally it cannot breathe under water, so as it dives a muscular action closes the blowholes (nostrils), which remain closed until the cetacean next breaks the surface. When it does, the muscles open the blowholes and warm air is exhaled.

To make this easier, the cetacean's blowholes have moved to the top of its head, giving it a quicker chance to expel the stale air and inhale fresh air. When the stale air, warmed from the lungs, is exhaled it condenses and vapourises as it meets the cold air outside. This is rather like when you breathe out on a cold day and a small cloud of warm air appears. This is called the 'blow', or 'spout', and each cetacean's blow is different in terms of shape, angle and height. This is how cetaceans can be identified at a distance by experienced whalers or whale-watchers.

The cetacean's eyes are set well back and to either side of its huge head. This means that cetaceans with pointed 'beaks' (such as dolphins) have good binocular vision forward and downward, but others with blunt heads (such as the Sperm Whale) can see either side but not directly ahead or directly behind. The eyes shed greasy tears which protect them from the salt in the water. Cetaceans also have an almost spherical lens in their eyes, which is most efficient at focusing what little light there is. However, their vision is generally quite poor (with the exception of the dolphin), which cetaceans make up with their excellent hearing abilities

Akin to the eyes, the cetacean's ears are also small. Life in the sea accounts for the cetacean's loss of its external ears, whose function is to collect sound waves and focus them in order for them to become strong enough to hear well. However, sound waves travel faster through the water than in the air, and so the external ear was no longer needed, and is no more than a tiny hole in the skin, just behind the eye. The inner ear, however, has become so well developed that the cetacean can not only hear sounds tens of miles away, but it can also discern from which direction the sound comes.

Some cetaceans are capable of echolocation. Mysticeti have little need of it, as they prey upon small fish that would be impractical to locate with echolocation. Some members of Odontoceti, such as dolphins and porpoises, perform echolocation. Many toothed whales emit clicks similar to those in echolocation, but we have yet to prove that they echolocate. Cetaceans use sound in the same way as bats - they emit a sound (called a click), which then bounces off an object and returns to them. From this, cetaceans can discern the size, shape, surface characteristics and movement of the object, as well as how far away it is. With this ability cetaceans can search for, chase and catch fast-swimming prey in total darkness. It is so advanced that most cetaceans can discern between prey and non-prey (such as humans or boats), and captive cetaceans can be trained to distinguish between, for example, balls of different sizes or shapes.

Cetaceans also use sound to communicate, whether it be groans, moans, whistles, clicks or the complex 'singing' of the Humpback Whale that is becoming so popular on wildlife documentaries and relaxation tapes.

Adapted from the Wikipedia article "Breathing Seeing Hearing and Echolocation", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki