Dolphins have eyelids

The senses of the dolphins

Seeing

Since the refractive index of water is higher than that of air, people can only see blurred in water, as the image is created behind the retina. The dolphins, on the other hand, have a softer lens and can thus adapt their shape to the environmental conditions. Its own glands continuously release a thick, transparent mucus that protects the eyes from the aggressive sea water. When the dolphin is above water, you might think that it is crying - but that is wrong because the dolphin has no tear glands.
The dolphin's eyelids act as a shutter. In low light they are wide open, in bright light they keep closing. Dolphins have their eyes completely closed in their sleep.
Many species of dolphins can only perceive two-dimensional images because the eyes are not in front, but to the side. Spatial vision is only possible in animals whose eyes are at the front of the head, so that both fields of vision overlap. But together with the sonar, spatial images are created again in the brain.

The sense of touch

The sense of touch is extremely important for the dolphins' daily life. It enables the dolphin to perceive the tiniest turbulent disturbances and pressure differences across the skin. The detection of turbulent disturbances is important in order to adapt the skin to the flow conditions and thereby avoid greater turbulence when swimming.
The dolphins also have a particular fondness for exchanging caresses. Touch plays a crucial role in a dolphin's life.

The sense of smell and taste

Odors do not spread as quickly in water as they do in air. Therefore it is not particularly important for the dolphins to be equipped with a sense of smell. Instead of the sense of smell, the dolphin is equipped with a sonar. With the help of the eyes and the sonar, the dolphin can recognize the environment and prey.
The taste buds on the tongue are present in dolphins. However, it is unclear whether these can also be used accordingly.

The hearing

It is anything but calm in the sea. Natural noises are created e.g. by waves and by living beings. The processing of the sound is favored by the fact that sound waves propagate five times faster in water than in air. Furthermore, the sound is carried much further.
In order to be able to evaluate all these noises, the dolphin has extremely fine hearing.
The dolphins' ears are directly behind the eye and can only be seen from a very short distance. In contrast to humans, dolphins can also determine the direction of a sound source underwater. The hearing limit with the help of the eardrum is similar to that of humans, approx. 20,000 Hz. At higher frequencies, other organs are also involved (lower jaw, sonar).

The sonar

The term sonar comes from English (Sound Navigation and Ranging). The dolphins have sonar parallel to their hearing, which is used to generate and perceive ultrasonic sounds, especially underwater. The principle of sonar is relatively simple. The dolphin emits a directional signal that is reflected back from the target and returns to the starting point. Then it is collected and analyzed. The echo provides the dolphin with information about the distance and the shape of the object.

The sense of direction

For dolphins, orientation under water is essentially based on the relief of the ground. You can remember this and remember it too. In addition, they can also use the ground magnetic field to orientate themselves (similar to bats, sea turtles, and whales). Dolphins may be able to remember the fluctuations in the magnetic field and orientate themselves accordingly. However, this is a hypothesis.