While cetaceans adapted to survive in an underwater environment 47 million years ago, they still have the senses generally found in land mammals. Humans have five senses: sight, hearing, smell, taste, and touch. Cetaceans have two more: echolocation and magnetic sense.
Hearing: Whales have specialized ears that are designed to hear sounds underwater. They use their sense of hearing to navigate the ocean, find food and communicate with each other. Whales have a different ear structure from ours and that of other mammals, so they process sound differently. The ear, or auditory canal, that connects the outside with the inside is blocked or limited; to compensate for this, whales have jawbones that function as sound transmitters to the inner ears. Each of their ears receives sound independently of the other. The middle and inner ear (tympanic bulla) are acoustically isolated from the skull by foam- filled air spaces, an adaptation that helps the whales to distinguish the direction of underwater sounds.
Whales produce sounds of various types, frequencies, and strengths. Dolphins use clicks and whistles to communicate with other members of their group; they can also use these to identify other species and even individuals. Sperm whales produce patterns of sound known as ‘coda’; this is used as an acoustic signature for each whale in a group. Orcas also have unique ‘dialects’ which are used for distinguishing family groups.
Great whales make the loudest sounds. Fin and blue whales make sounds with such low frequencies that we cannot hear them. The good news, however, is that with adequate equipment, these frequencies can be detected over distances of up to 1.600 km. Whales use these vocalizations and their hearing to communicate and navigate the depths of the dark ocean. Researchers estimate that some of the lowest-frequency sounds can travel through the ocean as far as 16.000 km without losing power. This equals the distance between Reykjavík and Brisbane in Australia.
Most of the frequencies whales use in their vocalizations are between 30 and 8.000 hertz. Water in the ocean has different layers because of the varying salt content and temperature; sound reflects between the layers, providing channels for concentrated sound that carries over long distances.
EcolocationTo get a sense of their surroundings, all toothed whales use a technique known as echolocation. Through echolocation, whales bounce sounds off objects in the environment: when the echo returns to them, they are able to decode information such as the distance of the object, how fast it is moving, its direction, its size, and whether it is dense or hollow. Not only this, but their echolocation is also so advanced that they are able to tell whether the object is a form of food, a predator, or an inanimate object.
Echolocation is extremely valuable when there is no light available, in the night or deep in the ocean for example. Whales are not the only animals with this ability; bats use echolocation to navigate in the night and when hunting, and also some bird species and rodents.
TasteTaste buds are visible on the tongues of some whale species, but scientists believe that four out of five taste receptor genes may be pseudogenized – i.e. the genes for taste might have lost their function. The five taste modalities are: sweet, salt, sour, bitter and umami.
The salt taste receptor genes are evolutionarily conserved in toothed and baleen whales and may help them regulate sodium levels and blood pressure.
SmellBaleen whales may have a limited sense of smell, used for detecting krill or plankton when they come up for air. On the other hand, toothed whales appear to have completely lost their olfactory system. This is the result of evolutionary processes. It is reasonable to assume that as the repositioning of the nostrils to the top of the head was occurring, many changes to the function of the organs associated with the nostrils must have also occurred.
Magnetic senseSmall crystals of magnetite have been found in many species including bacteria, bees, butterflies, fish, birds, bats, and reptiles. They have also been found in and around the brains of cetaceans. These crystals are believed to continuously orient themselves towards the earth’s magnetic field. This phenomenon is not very well understood, but the animals are believed to sense the orientation of the crystals, which indicate the direction they are traveling. Magnetic fields normally run north to south at an even density, but they may occasionally become distorted by certain geographical formations that are rich in metals like iron. This may be a cause of whale strandings. Similarly, solar flares, that create the aurora in the winter sky, may cause whale strandings in the same way.
VisionWhales do not see as well as humans and other terrestrial mammals; they see details ten times worse than humans. Their asymmetrical pupils allow them to use different areas of their retina, according to the light intensity. This is why these animals can see well in both water and air. On the downside, however, their sight is limited to only a few meters.
Species with short snouts or pointed beaks have binocular vision. Larger whales, like sperm whales, have their eyes positioned far back from the snout. They have monocular vision – meaning that each eye sees a separate part of the total visual field.
Mammals have two types of photoreceptors in their retinas – rods and cones. Cones give mammals color vision and are responsible for high spatial acuity. Rods let mammals see when light levels are low.
Most mammals have XNUMX types of cones in their eyes. Toothed whales’ eyes contain one type of cone, while baleen whales have none. This is why whales are believed to be largely colour-blind. On the other hand, whales’ eyes have many rods, so they seem to have evolved night vision.
TouchThe skin of a whale is very sensitive to touch. This may come as a surprise to some who imagine it to be a thick, leathery layer. However, it is actually very thin and smooth and feels like a peeled hardboiled egg to touch. It is the layer of blubber beneath the skin that may give it the appearance of being far tougher than it really is. Cetacean skin is made up of 80% water and is especially sensitive around the genital area, blowhole, flippers, and belly.
Touch seems to maintain order within social groups. Stroking or touching is also a part of courtship rituals in most species. Mothers and calves frequently touch each other to reaffirm their bond.