Why do most animals have black noses

Seeing in animals

How do animals see the world? Similar to us?

This is the question that cats and dogs have been asking themselves for a long time. Now you can see a little more clearly here. For a long time it was believed that animals only saw the world in black and white. Today we know that this is wrong. Not only is color vision widespread among animals - depending on the species, their eyesight can also be significantly better than ours. Visual acuity differs from species to species. It varies depending on the environment in which the animals live, at what speed they move, what prey they hunt or what predators they have to flee from.

 

To understand the differences between different animal species, let's use the human eye as a guide. It is characterized by particularly good general vision, which is able to adapt to practically all situations on land (underwater our lens cannot deform sufficiently to accommodate, we see blurred). With its sharpness, resolution, contrast and movement sensitivity, it is equally suitable for near, far and night vision. This versatility is typical of the human eye. The flip side of the coin is that it does not excel in any single area as it does with animals.

The night vision

For humans, “all cats are gray at night”, and shapes are also more difficult for them to see at night. The reason: only the rods, the light-sensitive cells of the retina, work. The latter require very little light to react and thus ensure that we can see at night - in contrast to the cones, which are responsible for colors and details.

Compared to humans, dogs can see very well at night. On the one hand, because his retina contains many more rods than human's, and on the other hand, because his pupil is able to position itself very wide. This is how he sees even in very weak light.

After all, it has a reflective membrane behind the retina, the so-called tapetum lucidum, which allows it to use even the smallest bit of light. This device makes the eyes of dogs (and other animals) glow at night when they are illuminated with a light source.

The more an animal's life is determined by nocturnal activity, the greater the number of rods in the retina compared to the cones. In exclusively nocturnal animals, such as owls or eagle owls, the pupil is round and large and very expandable, so that the eye can absorb as much light as possible during the night. It is also slit so that it can be closed more easily than a round pupil.

Controversial results

How did you come to these conclusions? On the one hand, changes in the behavior of the animals were examined and, on the other hand, spectrophotometric studies of the radiation absorbed by the retina were carried out. But since there is no concrete confirmation, the results obtained in this way are considered controversial.

The various theories agree on at least one point: the eye of a mammal is very similar to that of humans as a whole. Like humans, the shrew and the squirrel have perfect trichromatic vision, which means that their eyes react to blue, green and red (see box). The mouse and rat can see very well at night, but have poor color perception. Rabbits have difficulty recognizing certain colors, but can easily distinguish between blue and green. The horse can recognize some colors (yellow and green) better than others (blue and red), but also certain nuances (light and dark). After all, cattle allegedly cannot see red. So bulls are not attracted by the color of the red cloth, but by the movement of the fronds in front of their eyes.

  
 Twilight and night Strong light

Dogs, cats, etc.

Dogs cannot see yellow, red, and orange, nor can blue. So your color palette is in the green area. By the way, they are also slightly farsighted: at 25 cm they see a little blurred, so that they have difficulty seeing an immovable object right in front of their nose. Your visual acuity here is six times less than that of the average person. But they have other advantages: A German Shepherd can recognize the movement of its master even at a distance of 1.5 km. They also have better peripheral vision than we do, which is partly due to the lateral position of their eyes.

 

Cats see dichromatic: Research on their retinas has shown that they contain two types of cones, one reacting to blue and the other to green. So a cat cannot see red.

Your eye is adapted to your activity as a night hunter: there are chopsticks in large quantities. They cannot see anything in total darkness, but the starlight is enough for them to go hunting and prey on animals. To protect your very sensitive eye, the pupil closes to form a narrow slit when the light is fully incident. Overall, a cat's eyes are very well adapted to night vision, but not particularly efficient during the day. They only accommodate poorly and do not depict objects very precisely.

In contrast to that of the cat, the eagle's eye is tuned to track down prey during the day and at great distances. His retina must give him a very precise picture of a distant object. Its eyeball is relatively large and its retina contains more cones than rods. The eagle can therefore see excellently during the day; here he can accommodate quickly and easily. However, as soon as the light fades, his eyesight drops rapidly. He can therefore only hunt between sunrise and sunset. Another example: the rabbit. For him, looking up close is of little use. However, since it is a potential victim for land and air predators, it needs very good all-round visibility. His field of view is therefore 360 ​​°. Even if he cannot see clearly, his eye can see very precisely from which direction a movement is coming. So he can flee into his den very quickly. The same goes for most rodents.

The same flower seen by human beings and by a bee. Bees do not perceive the wavelengths of red, but they do recognize the wavelength of the ultraviolet that escapes our eyes.

What else is worth knowing

There are two types of photoreceptor cells in insects: ocells or single eyes, which react to light intensity, and compound eyes, which contain a large number of light-sensitive cells (8000 in bees). They enable the insect's nerve center to compose an image from the information transmitted by the compound eyes. A compound eye transmits 200 images per second, while the human eye perceives around 24 images per second. The sensitivity of compound eyes varies depending on the species.

 

In vertebrates, fish are said to see all colors, from red to purple, including ultraviolet, but they do not have good night vision, with the exception of pikeperch. Some predatory fish, such as the trout, have a field of view of 180 degrees. With reptiles, we know that a turtle can distinguish between blue, green and orange. The lizard recognizes yellow, red, green and blue.
Finally, birds have a very highly developed color perception and seem to adapt their behavior to color rather than to shape and movement.

 

The light spectrum

The light from the sun spans a spectrum that ranges from infrared to ultraviolet. The human eye can only perceive part of the light between red and purple. For example, it does not recognize ultraviolet, it is filtered out by the cornea and retina. But some animals, such as lobsters, goldfish and trout, bees, turtles, swallows and pigeons, can recognize it.

 

At the other end of the light spectrum, infrared rays are invisible to humans, but the heat released by infrared radiation from their prey can be perceived by some species of snake.

The four elements of sight

The color perception

In humans, it is possible due to the presence of three types of uvula in the retina, which are sensitive to green, blue or red. In some cases, one or more types of these suppositories are poorly developed. The most common form, red-green blindness, leads to confusion between green and red. In the most pronounced form of color blindness, there is no color perception at all, so everything is only seen in shades of gray from black to white. Some animals have more suppositories: some birds have four species, some butterflies five, and the manta ray even 30.

The perception of movement

It depends on the content of photoreceptors (light receptors) in the retina and their resistance during the visual process. Most animals can perceive movement very well because this is essential for them to survive - either to protect themselves from a predator or to hunt prey. The prey hunters snap for food that moves, but would starve to death next to a dead animal.

The field of view

This is the visible part of the room when the eye is not moving. In vertebrates, the field of view is fairly constant: its average is 170 °. The field of vision for humans is 200 °, 180 ° for falcons, 287 ° for cats and 360 ° for rabbits.

The position of a dog's eyes allows the animals a larger field of view from the side. So you see more than we do.

The perception of space

It is made possible by the field of vision, by the movement of the eyeball and the head. Nevertheless, there are animals whose spatial perception works differently: They are equipped with sonar that allows them to “see” sound waves - bats are one of them.