Vision is the most developed sense organ in birds. The eye is a globular formation covered with many membranes.

From outside to inside (except for the front of the eye), the following membranes are located: sclera, vascular, pigment and retina. In front, the sclera continues with the transparent cornea, and the vascular - with the ciliary body and the iris. Under the influence of contraction of the muscles of the iris, the opening in it - the pupil - changes in size. Directly behind the iris lies the lens, and between it and the cornea is a small, fluid-filled anterior chamber of the eye. Behind the iris and lens, the optic cup is filled with a gelatinous vitreous humor.

The most striking difference between the bird eye and the mammalian eye is the absence of retinal blood vessels; but instead, the bird's eye has a special vascular structure that protrudes into the vitreous humor — the crest. Another difference is the presence in the retina of birds of two or even three pits (fovea) - areas of sharper vision. These areas are especially developed in birds of prey. The muscles of the ciliary body and iris are striated, and in mammals they are smooth. The sclera in birds and reptiles is reinforced with bony plates in its anterior part. Most of these differences represent adaptation to vision during flight and directly or indirectly contribute to the sharper vision of birds compared to mammals. Because of this, the birds are called Augentiere. Due to the fact that in birds each eye is connected to only one side of the brain (complete intersection of nerves), the visual perception of each eye is independent and binocular vision in birds is less important than monocular vision.

The development of the eye takes place in the dark; the eye is, as it were, protected from premature activation of the function. The eye vesicles, which have arisen as protrusions of the diencephalon, turn into real vesicles with compression at the base by 40-45 hours. incubation. From 50-55 hours. there is significant progress in the development of the eye. The eye vesicles begin to bulge, forming a double-walled cup, and the hollow stalk that connects them to the brain becomes increasingly narrower. The inner layer of the eye cup (originally the outer wall of the eye vesicle) - the retinal primordium becomes thicker than the outer one, which is the primordial layer of the pigment layer, the iris and the ciliary body. The eye cup has an opening facing outward and downward. The outer part becomes the pupil, and the lower, which subsequently closes, is called the choroidal, or embryonic, slit. Its closure is closely related to the development of the ridge.

The lens develops separately from the ocular vesicle as a thickening of the superficial ectoderm in a 40-hour chick embryo. This thickening is then invaginated, and in 62-74-hour embryos, the lens vesicle is separated from the superficial ectoderm. The walls of the crystalline vesicle thicken, and its cavity disappears. The lens cells stop dividing, lengthen, the nuclei in them disappear and become fibrous. The lens of a hatched chick contains more than 500 layers of fibers, and the process of their formation continues after hatching. The precipitin test showed the presence of adult lens proteins in the lens vesicle of a 60-hour embryo. Consequently, the chemical differentiation of the lens precedes the morphological one. The lens capsule (bag) is, apparently, a product of the activity of its cells. Zinn ligaments are attached to it, extending from the ciliary body. In a 4-day-old embryo, the upper edges of the eye cup converge on the sides of the lens.

The main part of the eye that perceives visual images is the retina, located between the pigment epithelium and the vitreous body. The retina consists of 5 layers: ganglion, internal reticular, internal nuclear, external reticular and external nuclear. Light, passing through the cornea, pupil, lens, vitreous humor and retina, is reflected from the pigment layer. The processes of visual cells (their nuclei are located in the outer nuclear layer) are directed to it, which perceive light: rods (black and white) and cones (color image). In daytime birds, cones predominate in the retina, while in nighttime birds, rods predominate. Light-induced stimulation is transmitted through the axons of visual cells to the synapses of the dendrites of bipolar neurons (whose nuclei are located in the inner nuclear layer), and one bipolar neuron unites up to 30 visual cells. The axons of the bipolar synapses with the dendrites of the ganglion cells, the axons of which grow along the groove in the wall of the eye stalk towards the brain and form the optic nerve.

The retinal fossa (area of ​​acute vision) appears in the center of a small thickened area, which appears to be the result of better blood supply due to early thickening of the choroid in this area. The fossa is formed as a result of radial migration of cells from the center of the site. In the area of ​​the fossa, there is the greatest accumulation of cones and rods. In birds hatching with closed eyes, the thickened platform and the fossa in it do not begin to develop until the moment of hatching, and the most rapid differentiation of the fossa occurs after the eyes are opened. The retina of birds is much thicker than that of other animals, its elements are more clearly organized, and the various sensitive layers are more sharply delimited. Different species of birds have differences in the structure of the retina - basically, this is a different ratio of rods and cones and the position and depth of pits, areas of acute vision. In the histological development of the retina of the chicken embryo, three periods can be distinguished:

1) reproduction of cells from the 2nd to the 8th day; 2) cellular rearrangement from 8th to 10th; 3) final differentiation after the 10th day of incubation. Neuroblasts and nerve fibers are present in the retina by the end of the 3rd day. Rods and cones begin to differentiate on the 10-12th day. By the end of incubation, the rods and cones in the retina of the chicken embryo reach the stage of development that is observed in the domestic sparrow only a few days after hatching. Govardovsky and Kharkeevich showed that in a 10-day-old chicken embryo, future visual cells have a cylindrical shape and are tightly attached to the pigment epithelium, which, apparently, plays an important role in supplying photoreceptor cells with vitamin A from the pigment epithelium. Vitamin A is necessary for the construction of molecules of the visual pigment - rhodopsin - and those membrane structures in which it is localized. On the 18-19th day of incubation, the structure of the receptor cell becomes more complex due to the inclusion of rhodopsin in it.

Here are several works on the histochemistry of the development of the retina of a chicken embryo. The content of acetylcholine and cholinesterase activity in the retina increases evenly from the 8th to the 19th day of the development of the chicken embryo, and then sharply increases. Alkaline phosphatase activity also suddenly increases between days 17 and 19. Apparently, the nerve elements of the retina mature by the 19th day and are able to conduct impulses, since the reflex of the constriction of the pupil can be evoked for the first time precisely at this time. Vinnikov's employees have shown that: 1) vitamin A is involved in the regulation of the release of ions in the light and in the dark and determines the state of general excitation of the receptor; 2) in the retina there is succinic oxidase and cytochrome oxidase activity, apparently indicating the transport of electrons and the regeneration of ATP; 3) the activity of oxidative enzymes in the mitochondria of photoreceptors, as a rule, increases in the light and decreases in the dark; when illuminated, the mitochondria of the rods swell, and the mitochondria of the cones do not change.

The crest of the eye varies greatly in size and shape in different bird species. It is a thin, dark-pigmented plate that fan-folds and protrudes into the vitreous from the ventral surface of the eye. The ridge can have 5 to 30 folds and be short or long, reaching the lens. It consists mainly of a vasculature supported by pigmented connective tissue (glial cells). On the 6th day of development of the chicken embryo, the ridge protrudes into the vitreous body in the form of a low ridge along the line of confluence of the walls of the choroidal fissure. The pigment appears in it after 8 days, and folds begin to form on the 9-10th day of incubation. In adult birds, the crest is completely penetrated by capillaries, and arteries and a vein lie at the base of it. It is possible that the ridge, in addition to supplying the retina with nutrients, also protects it from strong light. In addition, Dement'ev's review indicates that the crest plays a role in vitreous nutrition and possibly serves to warm the eye and increase visual acuity.

The edges of the eye cup facing forward form an iris by the 8-9th day, and muscle fibers begin to appear in it from the 7th day. The muscles of the iris: sphincter (for pupil contraction) and radial (for pupil dilation) are striated, which causes an arbitrary contraction of the pupil (especially manifested in birds of prey). The sphincter muscle appears on the 8-9th day, and the radial muscle appears on the 13-19th day. The color of the iris is due to pigment cells, pigment corpuscles and colored fat droplets.

The folds of the ciliary body (from 85 to 150 in adult specimens of different bird species), located in the center of the iris, diverge radially from the lens along the meridians of the eye. The ciliary processes (the central ends of the folds) extend beyond the border of the iris, and the ligaments (zinn), extending from the grooves between them, are attached to the lens bag. The first ciliary processes appear on the 6-9th day of the development of the chicken embryo and consist initially of the outgrowths of the mesenchyme directed towards the lens. In a 16-17-day-old chicken embryo, there are already about 90 of them. The ciliary body secretes fluid from the anterior chamber of the eye, due to which diffuse nourishment of the lens and cornea is carried out and intraocular pressure is regulated.

The rudimentary ciliary muscle appears on the 8th day in the form of a bundle of myoblasts; its transverse hairiness is first seen in an 11-day-old embryo. Contraction of the ciliary muscle, acting on the sclera, shrinks the equatorial diameter of the eyeball, increases intraocular pressure, and pushes the lens and front of the eye forward for close vision. According to another theory, the ciliary muscle acts on the cornea, which indirectly changes the tension of the ridge ligament and changes the shape of the lens. Dementyev believes that the accommodation of the eye in birds occurs in all three ways: by changing the shape of the lens, the shape of the cornea, and the distance between the cornea and the lens.

The corneal epithelium (conjunctiva) originates from the ectoderm, but the underlying corneal portion originates from the mesenchyme. The cornea performs two functions: coarse focusing of the eye and goggles. That part of the eye of a chicken embryo, where the vitreous body will form, on the 4th day of development Consists of a fibrous mesh of an indefinite structure.

The choroid and sclera arise from the mesenchyme, which covers the eye cup during embryonic development and is also involved in the formation of the ciliary body and cornea. The choroid provides nutrition to the eye. The early development of the choroid consists in the condensation of the mesenchyme in contact with the outer layer of the eye cup, which is noticeable already in a 5-day-old embryo. Further - on the 13-14th day - the size of the capillary network of the choroid increases, and then a layer of larger vessels appears outside it; tissue pigmentation begins on the 8th day. The inner surface of the choroid has a so-called "mirror" (tapetum lucidum), which reflects light and irritates the retina with its reflection, which allows it to capture visual impressions in low light. The development of the sclera begins simultaneously with the choroid, and on the 9th day, early protein bones can already be distinguished in it.

On the 7th day of development of the chicken embryo, an integumentary circular fold with a hole in the center forms in front of the eyeball, which later turns into the lower and upper eyelids. Inside it, a semicircular fold is simultaneously formed on the side of the beak - the blinking membrane, or the third eyelid. In a chicken embryo, the eyelids are closed until the 18th day of incubation, and in some chick birds (passerines, woodpeckers, cuckoos, etc.), the eyelids open only a few days after hatching.

The eyes are a special organ that is endowed with all living things on the planet. We know in what colors we see the world, but how do animals see it? What colors do cats see and which ones do not? Is vision black and white in dogs? Knowledge about the eyesight of animals will help us take a broader look at the world around us and understand the peculiarities of the behavior of our pets.

Features of vision

And yet, how do animals see? According to some indicators, animals have more perfect vision than humans, but it is inferior in the ability to distinguish between colors. Most animals see only in a specific palette for their species. For example, for a long time it was believed that dogs see only in black and white. And snakes are generally blind. But recent research has proven that animals see different wavelengths than humans do.

Thanks to vision, we receive more than 90% of information about the world that surrounds us. The eyes are for us the predominant sense organ. It is interesting that the vision of animals in its acuity is significantly higher than that of humans. It's no secret that predators see 10 times better. The eagle is able to detect prey in flight from a distance of several hundred meters, and the peregrine falcon tracks the pigeon from a height of a kilometer.

The difference is that most animals can see perfectly in the dark. The photoreceptor cells of the retina in their eyes focus the light, and this allows nocturnal animals to capture streams of light in several photons. And the fact that the eyes of many animals glow in the dark is due to the fact that a unique reflective layer called tapetum is located under the retina. Now let's take a look at certain types of animals.

Horses

The gracefulness of the horse and its expressive eyes can hardly leave anyone indifferent. But often those who are learning to ride are told that it is dangerous to approach a horse from behind. But why? How do animals see what is happening behind them? No way - the horse is behind its back and therefore it can easily get scared and kick up.

The horse's eyes are positioned so that it can see from two angles. Her vision is, as it were, divided in two - each eye sees its own picture, due to the fact that the eyes are located on the sides of the head. But if the horse looks along the nose, then it sees one image. Also, this animal has peripheral vision and sees excellent at dusk.

Let's add some anatomy. In the retina of any living being, there are two types of receptors: cones and rods. Color vision depends on the number of cones, and the rods are responsible for peripheral vision. In horses, the number of rods prevails over that in humans, but cone receptors are comparable. This suggests that horses also have color vision.

Cats

Many houses keep animals, and of course the most common are cats. The vision of animals, and especially of the feline family, differs significantly from that of humans. A cat's pupil is not round, like most animals, but elongated. It reacts sharply to large amounts of bright light by narrowing down to a small slit. This indicator says that in the retina of the eyes of animals there is a large number of receptor rods, due to which they see perfectly in the dark.

What about color vision? What colors do cats see? Until recently, it was believed that cats see in black and white. But research has shown that it distinguishes well between gray, green and blue colors. In addition, he sees many shades of gray - up to 25 tones.

Dogs

Dogs' vision is different from what we are used to. If we return to anatomy again, then in the eyes of a person there are three types of cone receptors:

• The first one perceives long-wave radiation, which is distinguished by orange and red colors.
• The second is medium wave. It is on these waves that we see yellow and green.
• The third, respectively, perceives short waves, in which blue and violet are distinguishable.

The eyes of animals are distinguished by the presence of two types of cones, which is why dogs cannot see orange and red colors.

This difference is not the only one - dogs are farsighted and see moving objects best. The distance from which they see a stationary object is up to 600 meters, but dogs notice a moving object from 900 meters. It is for this reason that it is best not to run away from the four-legged guards.

Sight is practically not the main organ in a dog, for the most part they follow smell and hearing.

Now let's summarize - what colors do dogs see? In this, they are similar to color-blind people, they see blue and purple, yellow and green, but a mixture of colors may seem to them just white. But best of all, dogs, like cats, distinguish gray colors, and up to 40 shades.

Cows

Many believe, and we are often presented, that domestic cloven-hoofed animals react sharply to red. In reality, the eyes of these animals perceive the color palette in very blurry fuzzy tones. Therefore, bulls and cows react more to movement than to how your clothes are colored or what color they wave in front of their face. Interestingly, and who will like it if they start waving a rag in front of his nose, sticking, in addition, a spear into the scruff of the neck?

And yet, how do animals see? Cows, judging by the structure of their eyes, are able to distinguish all colors: white and black, yellow and green, red and orange. But only weak and blurry. Interestingly, cows' vision is similar to a magnifying glass, and for this reason they are often frightened when they see people unexpectedly approaching them.

Nocturnal animals

Many nocturnal animals have a tarsier, for example. This is a little monkey that goes hunting at night. Its size does not exceed a squirrel, but it is the only primate in the world that feeds on insects and lizards.

The eyes of this animal are huge and do not turn in their sockets. But at the same time, the tarsier has a very flexible neck that allows him to rotate his head 180 degrees. He also has extraordinary peripheral vision, allowing him to see even ultraviolet light. But tarsier distinguishes colors very poorly, like everyone else.

I would also like to say about the most common inhabitants of cities at night - bats. For a long time it was assumed that they do not use sight, but fly only thanks to echolocation. But recent studies have shown that they have excellent night vision, and moreover, bats are able to choose whether to fly to sound or turn on night vision.

Reptiles

Talking about how animals see, one cannot remain silent about how they see snakes. The tale of Mowgli, where a boa constrictor bewitches monkeys with its gaze, is awe-inspiring. But is it true? Let's figure it out.

Snakes have very poor eyesight, this is affected by the protective shell that covers the reptile's eye. From this, the named organs seem cloudy and take on that terrifying appearance, about which they make legends. But vision for snakes is not the main thing, basically, they attack moving objects. Therefore, the tale says that the monkeys sat in a daze - they instinctively knew how to escape.

Not all snakes have some kind of heat sensors, but they still distinguish between infrared radiation and colors. The snake has binocular vision, which means it sees two pictures. And the brain, quickly processing the information received, gives it an idea of ​​the size, distance and outlines of a potential victim.

Birds

Birds are striking in a variety of species. It is interesting that the vision of this category of living beings is also very different. It all depends on what kind of life the bird leads.

So, everyone knows that predators have extremely keen eyesight. Some species of eagles can spot their prey from a height of more than a kilometer and fall down like a stone to catch it. Did you know that certain species of birds of prey are able to see ultraviolet light, which allows them to find nearby burrows in the dark?

And the budgie living in your house has excellent eyesight and is able to see everything in color. Studies have shown that these individuals distinguish each other with their bright plumage.

Of course, this topic is very broad, but we hope that these facts will be useful for you to understand how animals see.

These mysterious feelings

Bird vision

We are used to looking at the world with two eyes at once, using binocular, deep vision. In most birds, the eyes are located on the sides of the head - this expands the general field of view, but narrows the binocular one. But birds can use their eyes independently. Just as we can take one object with one hand and the other with the other and manipulate them separately, a seagull patrolling a pond can keep its left eye on its neighbor on the left, and with its right eye on its neighbor on the right, not forgetting to look down with two eyes immediately. The total field of view, consisting of monocular and binocular, in gulls, sparrows and pigeons is slightly more than 300 °, in chickens - 320 °, and in nightjar - 340 °! Binocular vision is only a special case of visual perception of birds. In humans, it is 150 °. No one of the birds can catch up with him in this. Even for an owl and nightjar it is only 60 °, for a pigeon - 25-30 °, for a sparrow, bullfinch, chaffinch - 10-20 °, and for a cuckoo it does not exist at all. The eyes of the woodcock sandpiper are peculiarly located. They are large, convex, and so displaced backward that the binocular field is formed not in front, but behind.

When a woodcock at feeding sticks its beak into the ground, it perfectly sees what is happening directly behind it. In herons, the binocular field is displaced downward under the beak. This is due to their manner of hiding, raising their beak vertically upward. At the same time, the eyes turn slightly downward, and the bird observes what is happening in front of it with two eyes at once. The use of binocular vision is very important for an accurate assessment of distance, perception of the depth of space and all movements of objects in it. Thanks to binocular vision, swallows, for example, successfully catch small insects in the air, and the shrike demonstrates aiming throws when hunting nimble lizards and mice. In the eyes of these birds, there is a second lateral area of ​​acute vision with a fossa. They all hunt for active, mobile prey. In addition to shrikes and swallows, these are hawks, falcons, terns, bee-eaters, kingfishers and some others. During a search flight, they use monocular vision and a central retinal fossa, while chasing and catching prey, they use binocular vision with focusing on the lateral fossa.

Nature has endowed birds with the most developed eyes among all living creatures. The eyes of birds of prey can be equal in volume or larger than those of humans. All birds have excellent eyesight. A small bird such as a sparrow or tit, hawk, eagle or falcon can be seen from a distance of more than a kilometer.

Vision is the main factor in the far and near orientation of birds. Unlike other vertebrates, among birds there is not a single species with reduced eyes. In terms of relative and absolute sizes, the eyes of birds are very large: in large predators and owls, they are equal in volume to the eye of an adult. Increasing the size of the eyes is advantageous because it allows you to get a larger image on the retina and thus more clearly distinguish its details. The relative sizes of the eyes, which differ in different species, are associated with the nature of food specialization and the way of hunting. In herbivorous geese and chickens, the eyes by weight are approximately equal to the mass of the brain and make up 0.4-0.6% of the body weight, in birds of prey the weight of the eyes is 2-3 times greater than the weight of the brain and is 0.5-3% of the weight body, in owls active at dusk and at night, the weight of the eyes is equal to 1-5% of the body weight.

Some species that feed mainly on mobile objects (daytime predators, herons, kingfishers, swallows) have two areas of acute vision. Swifts have only one area of ​​sharp vision, so their methods of catching prey on the fly are less varied than that of swallows. A very flexible pupil prevents excessive "exposure" of the retina (during fast turns in flight, etc.).

The structure of the eyes of birds.

The basic structures of the bird's eye are similar to those of the eyes of other vertebrates. The outer layer of the eye in front consists of the transparent cornea and two layers of the sclera - a rigid layer of collagen fibers. Inside, the eye is divided by the lens into two main segments: anterior and posterior. The anterior chamber is filled with aqueous humor, while the posterior chamber contains the vitreous humor.

The lens is a transparent biconvex body with hard outer and soft inner layers. It focuses light on the retina. The shape of the lens can be changed by the ciliary muscles, which are directly attached to it by means of zonular fibers. In addition to these muscles, some birds also have additional Crampton muscles that can reshape the cornea, thereby providing a wider range of accommodation than mammals. This accommodation can be very rapid in diving waterfowl. The iris is a colored muscle diaphragm in front of the lens that regulates the amount of light that enters the eye. At the center of the iris is the pupil, a changing circular opening through which light enters the eye.

The retina is a relatively smooth, curved multilayer structure containing photosensitive rod and cone cells with corresponding neurons and blood vessels. The density of photoreceptors is important in determining the maximum achievable visual acuity. Humans have about 200,000 receptors per mm2, the house sparrow has 400,000 and the common buzzard (bird of prey) 1,000,000. Not all photoreceptors have an individual connection with the optic nerve; visual resolution is largely determined by the ratio of nerve ganglia to receptors. In birds, this indicator is very high: in the white wagtail, there are 100,000 ganglion cells per 120,000 photoreceptors.

The rods are more sensitive to light but provide no color information, while the less light-sensitive cones provide color vision. In daytime birds, 80% of receptors can be cones (up to 90% in some swifts), while in night owls, photoreceptors are almost exclusively represented by rods. In birds, as in other vertebrates, with the exception of placental mammals, cones are double. In some species, these double cones can account for up to 50% of all receptors of this type.

The analysis of visual perception is carried out in the visual centers of the brain. Retinal ganglion cells respond to several stimuli: contours, color spots, movement directions, etc. In birds, like in other vertebrates, the retina has an area of ​​the most acute vision with a depression in its center (macula).

In the area of ​​the blind spot (the entry point of the optic nerve), there is a ridge - a vascular-rich folded formation protruding into the vitreous humor. Its main functions are to supply the vitreous body and inner layers of the retina with oxygen, as well as to remove metabolic products. There is a comb in the eyes of reptiles, but in birds it is larger and more complex. The mechanical strength of the bird's eyes is provided by the thickening of the sclera and the appearance of bony plates in it. Many birds have well-developed mobile eyelids and a developed nictitating membrane (third eyelid), moving directly along the surface of the cornea, cleaning it.

Most birds have eyes on the sides of their heads. The field of view of each eye is 150-170 degrees. The field of binocular vision is quite small and in many birds is only 20-30 degrees. In some birds of prey (for example, owls), the eyes shift towards the beak, which increases the binocular field of vision. In some species with bulging eyes and a narrow head (some waders, ducks, etc.), the total field of view can be 360 ​​degrees, while narrow (5-10 degrees) binocular fields are formed in front of the beak (this makes it easier to grasp prey) and in the area the back of the head (this allows you to estimate the distance to the enemy approaching from behind). In birds with two areas of acute vision, they are usually located so that one of them is projected into the field of binocular vision, and the other into the field of monocular vision.

Angles of view.

All birds have excellent color vision, recognizing not only primary colors, but also their shades and combinations. Therefore, in the plumage of birds, bright color spots are so often found that serve as species markers. Birds distinguish not only the movement of objects and their contours, but also details of the shape, color, pattern, surface texture. That is why visual perception is used by birds both to obtain a variety of information about the world around them, and as an important tool in intraspecific and interspecific communication.

Birds rarely look up because it is more important for them to see everything that happens on earth. The design of the bird's eyes reflects the correctness of this statement. The upper segment of the bird's retina sees better (sees the ground), and the lower segment sees worse (the lens builds an inverted image). Some birds see well both in the air and in the water (for example, the cormorant). This assumes the possibility of accommodation (changing the refractive power of the optical system of the eye). Cormorant has the ability to change this characteristic by 4000 diopters.

Perception of contrast.

Contrast is defined as the difference in brightness between two colors divided by the sum of their brightness. Contrast sensitivity is the inverse of the smallest contrast that can be detected. For example, a contrast sensitivity of 100 means that the smallest contrast that can be seen is 1%. Birds have relatively low contrast sensitivity compared to mammals. Humans can see contrasts of 0.5-1%, while most birds need 10% contrast to get a reaction. The contrast sensitivity function describes the ability of animals to detect the contrast of patterns of different spatial frequencies.

Perception of movement.

Birds see fast movements better than people, for whom flickering at a speed of more than 50 Hz is perceived as continuous movement. Therefore, a person cannot distinguish between individual flashes of a fluorescent lamp vibrating at a frequency of 50 Hz. The hawk is capable of swiftly chasing prey through the forest, avoiding branches and other obstacles at high speed; for a person, such a pursuit will look like a fog.

In addition, birds are able to detect slow moving objects. The movement of the sun and stars across the sky is imperceptible to humans, but obvious to birds. This ability allows migratory birds to orient themselves during migrations.

To obtain a clear image during flight, the birds hold their heads in the most stable position, compensating for external vibrations. This ability is especially important for birds of prey.

Perception of the magnetic field.

It is believed that the perception of the magnetic field by migratory birds depends on light. Birds turn their heads to determine the direction of the magnetic field. Based on studies of neural pathways, it has been suggested that birds are able to see magnetic fields. The migratory bird's right eye contains light-sensitive proteins, cryptochrome. The light excites these molecules, which release unpaired electrons that interact with the Earth's magnetic field, providing directional information.

There are many varieties of birds, with better developed eyes than other living creatures of the same size. In birds of prey, the eye volume can be equal (sarich) or much larger (golden eagle) than in humans. At the same time, the human body weight is 3000 times greater than that of the golden eagle. In an owl, the weight of the eyes is equal to one third of the weight of the bird's head. All birds have excellent eyesight. A small bird, such as a sparrow, can be seen by a peregrine falcon at a distance of more than a kilometer.

Birds use hearing or sight to search for prey, since some of the species are devoid of smell. A vulture can spot a dead animal in the mountains at a distance of 2-3 kilometers. The head of birds can freely rotate up to 180 degrees, and in some species up to 270 degrees. Owls twist their heads more than others. The eyes of owls are motionless and, in contrast to other birds, look forward. That is why nature has provided the owl with the widest angle of head rotation, the absence of the need to turn around with the whole body allows it to track sources of noise, leaving the body in place and remain invisible to potential victims.

What other birds can boast of? The eyes of most birds are located on the side of the head, and at the same time they have a horizon of 300, and some even 360 degrees. And this - without turning the head, and without changing the position of the eyes. It is worth remembering that human vision only covers an angle of 150 degrees. But not all birds need such a wide angle of view. For example, predators do not need it.

The eyes of predators are directed forward and the angle of view is not too large (160 degrees in the kestrel), but the ability for binocular vision is much more developed in predators. At the same time, owls have this ability better than others. It is easier for predators to turn to an object from behind and examine it, but their prey needs a wide outlook both in flight and during feeding and other situations. A duck can spot a predator without turning its head.

In birds, the direction of the best visual acuity exists and is important. It is determined by the anatomy of the structure of the eye and differs significantly in different species of birds. Usually, the most acute perception in birds is sideways, due to which the bird in flight has two clear pictures. It is interesting to compare the vision of a swift and a swallow. When eating the same food, their eyes are arranged differently. The swift's gaze is directed forward, since it flies very quickly and cannot turn on the spot. And the swallow's keen vision is mainly directed to the side, it can notice the midge from any angle, at the same moment make a U-turn and overtake the flickering food. Therefore, when there is a lot of food, the swallow and the swift are in an equal position, and when there is little, then the swift can no longer feed.

Birds rarely look up. It is more important for them to see what is happening on earth. The design of the bird's eyes reflects the correctness of this statement. The upper segment of the bird's retina sees better (and sees the ground), and the lower segment sees worse. Some birds see well both in the air and in the water (merganser, cormorant). This presupposes the possibility of accommodation (change in the refractive power of the optical system of the eye). Cormorant has the ability to change this characteristic by 4050 diopters. And a person with good eyesight at 1415 diopters. The colors of the birds are distinguished, otherwise why would they have colored plumage. But the question remains open - do they see colors in the same way as people. The question has no answer yet.