Ways of orienting birds during long flights. How migratory birds navigate. Vision as a way of orientation in space

Perhaps the most extensive, representative and at the same time beautiful, amazing and little known to the point of mystery, the category of representatives of the fauna of our planet is birds. It seems that everything is in front of your eyes, that is, above your head, but so far not all the subtleties of their existence have been discovered and studied.

Despite the fact that a detachment of birds inhabits the Earth for about 160 million years (pterodactyls were the predecessors of birds), little is known about the seasonal migration of these creatures, about their long flights. And most importantly - about the unique possibility of orientation in the vast expanse of the globe.

Reading not so numerous publications and scientific studies, we can conclude that scientists began to study the orientation of birds in flights only about a hundred years ago. And there are still no unambiguous and specific answers to all questions of interest. Basically information at the level of hypotheses.

However, this is not surprising. It is believed that our civilization has passed only 5-7 percent of its existence, and the same path is behind science and other branches of knowledge.

I note that for two decades I personally had to deal with radar and visual control of airspace, in which birds were quite often the objects of detection as air targets. So I have some idea about this topic.

Specifically about the orientation of migratory birds in their flights

It is known that not all birds remain to winter in their habitats. How to sing Vladimir Vysotsky, "everything strives for warmth from frost and blizzards." Although this opinion of the bard is now disputed by opponent scholars.

Let's leave for now the fact that not all birds fly south. Some species prefer the northern fringes of the continent. But you must admit that the ability to overcome tens of thousands of kilometers twice a year with enviable perseverance every year and not be mistaken by the desired “airfield” sometimes causes amazement. After all, birds, like their competitors, have no man-made aircraft, no modern navigation equipment, no ground-based tracking and flight control systems that can at any time determine their location, check the course and correct the route.

What can be said about bird navigation?

Many options have been put forward by researchers. This is a visual orientation according to the terrain, infrastructure, railways and highways, cities. Well, this, perhaps, is true, but, first of all, for sedentary, relatively far-flying birds. Then the sun, moon, stars and their positions, other permanent factors. However, as the main ones, many of these hypotheses were sooner or later rejected not so much because of the diversity of bird species, but because of the even greater diversity of their behavior.

Nowadays, with the development of science, the hypothesis has become predominant that the orientation and navigation of migratory birds is carried out using the planet's magnetic field, which exists between the poles. This judgment was first expressed over 100 years ago by a Russian academician BUT. Middendorf. At first it was successful, and then it was either recognized or denied, without offering anything significant in return. For with the methods then used for verification, the idea could neither be proved nor refuted.

The experiments were mainly carried out on pigeons, which, as is known, are not migratory birds. Small magnets were attached to the head, paws or wings of birds to find out how they affect flight. Due to this, the normal flight was disrupted, but no answer to the questions that arose could be obtained.

Currently, the geomagnetic orientation of birds in the direction of flight (along with other landmarks) is allegedly proved theoretically and experimentally. It is interesting that at the command posts of the radio engineering troops, as a document, there is a “Map of Ornithological Situation” with established flight routes for birds. It is worth noting that the main route of migratory birds, starting in the Brest region, goes to the north-east of the republic, where it seems that the birds gather in large flocks, feed on a long journey, and then follow in a southerly direction. However, this is based on generalized long-term observations. Only.

Turning to more recent research

At the Zoological Institute in Frankfurt am Main, robins were placed in a large chamber, inside which artificial magnetic fields were created. With the help of these fields, it was possible to compensate for the geomagnetic field or create its other strengths. Birds were isolated from all other external landmarks.

In a normal geomagnetic field, the birds correctly chose the direction for their migratory flight. When the field was weakened by 2-4 times or doubled, the controlled ones randomly rushed around the chamber, losing all orientation. Gathered together again only outside the radiation zone. Similar disturbances in navigational abilities in migratory birds are also observed during strong magnetic storms.

By the way, about the sensitivity of birds to ultra-high frequency radio emissions. If anyone does not know, aerial targets, which include the detected dense flocks of birds, on the screens of radar stations have a mark similar to the mark of a real low-speed target, such as balloons, helicopters, light aircraft, meteorological formations or something else like that.

One of the proven ways to recognize the type of "bird or target" is to irradiate this target with direct radiation from the radar, in particular a radar altimeter. After some time of intense exposure, if the target is a flock of birds, it will disintegrate. This is how flocks of birds are recognized in practice.

And recently, for the first time, biologists put forward and substantiated the version of how migratory birds feel the magnetic field.

"There are two hypotheses, explains Dmitry Kishkinev, an employee of one of the universities of Canada, - magnetic and olfactory (olfactory). Currently, scientists are actively looking for magnetoreceptive organs that can serve as an internal compass for birds. According to one version, birds in the retina have certain photoreceptors that can see the magnetic field. It was kind of proved that the sensitivity to the magnetic field is tied to vision. It is believed that the retina contains photosensitive proteins - cryptochromes, which, under the influence of light and a magnetic field, can be excited in different ways depending on the orientation of its lines of force. The second option suggested that birds have a magnetically sensitive organ in their upper beak - 15 years ago, cells containing a large amount of iron oxide were found there. Scientists then decided that this is the desired magnetoreceptor, connected to the bird's brain by the trigeminal nerve.

That's where they stopped

Why? Yes, because the organs of birds in the context of resolving issues of interest are practically not studied thoroughly. Scientists share the ability in the orientation (choice of direction) of birds and navigation - the ability not only to maintain a strict direction of movement, but also to represent one's true location relative to the target.

Thanks to experiments that have been going on since the 60s, scientists believed that birds could navigate in several ways.

Researchers led by Kishkinev caught warblers at the Rybachy biological station (Curonian Spit, Kaliningrad region) in the spring, when birds fly north. According to ringing data, biologists know that these birds must fly for nesting either to the Baltic states, or to the northwestern part of Russia (to the Leningrad region, Karelia), or to the south of Finland. The birds caught were brought to Moscow by plane, and some of them were operated on: one half of the warblers was cut the trigeminal nerve, and the other half was made the same incision in the beak, but without cutting the nerve. This was done in order to exclude the impact on the navigation of birds of the very fact of the operation on the beak.

To find out how the operation will affect the navigation of birds, they were brought to the biological station of Moscow State University near Zvenigorod, but for some reason they were not released. The cage method was used to study the migratory behavior of birds. Emlena. It is a cone with a mesh on top through which the bird can see the stars. The essence of the method is as follows: during the migration season, the bird is placed in this cage, and when it starts migrating "drive", it starts to jump and leave traces on the walls of the cone in the direction where it needs to fly by natural call. The experiment, the results of which were published in the scientific press, showed that birds with a severed nerve did not feel that they had been transported - they continued to navigate to the northeast, believing that they were still in the Kaliningrad region. And the falsely operated birds realized that they were a thousand kilometers from the place of capture, and compensated for the direction from the northeast to the northwest.

Scientists believe that the severed nerve transmitted some information to the bird's brain, most likely through a magnetic field, about its current location on the surface of the Earth. But in order to know its location, a bird either needs to have a "grid" of the Earth's magnetic field or know the nature of its change in longitude and latitude.

But where is this "grid" and how to know the field change?

“It seems to me that the mesh option is very complicated, because nature always chooses less precise, but simple mechanisms. Most likely, the birds feel that when moving, the field strength grows too much, and when a certain threshold that is genetically set is exceeded, the bird switches on "emergency plan". Instead of flying northeast, her on-board computer switches to "fly northwest"– explained the author of the study.

So this experiment could be considered incomplete. Moreover, the magnetic receptors themselves have not yet been found in the mandible; moreover, recent studies have shown that iron-containing cells are not nerve cells, but macrophages that consume bacteria. And such cells are found not only in the beak, but also in other tissues.

That is, we have a situation that has developed not in favor of modern world science: many observations confirm that birds are perfectly oriented, especially during long seasonal flights over vast distances - flying over vast ocean expanses without visual "control points", not only along the Earth's magnetic field, but also by adjusting its routes taking into account the magnetic declination, that is, making an allowance for the angular divergences of the directions of the geographic and magnetic poles of the Earth. But to find the biological mechanism for determining these magnetic meridians, that is, the notorious "bird compass", and to find out the principle of its operation, a person is not yet able to.

But there was another bold and unexpected version. If “migration anxiety” is one of the important reasons for the beginning of bird migration, then the question arises: is not the increase in magnetic activity (approximately twice) that occurs on Earth twice a year - during the periods of spring and autumn equinoxes - during periods their (birds) migration?

That is all that can be said for today. There are hypotheses, but man, the "king of nature", cannot yet go further.

Just some information

The Common Tern left its nest in Finland around 15 August 1996 and was caught on 24 January 1997 in Australia. She flew 25,750 km. The flight altitude usually does not exceed 3 thousand meters, however, there have been cases of climbing up to 6,300 meters (radar measurements).

The main migration routes from the European part of Russia: out of almost two hundred species of migrating birds, 16 go to Australia, 16 go to North America, 5 go to South America, 95 go to Africa.

Swans, storks, cranes and geese fly in families or large communities. Storks during long flights can periodically fall asleep on the fly for 10-15 minutes.

The flock, as a rule, is led by the most experienced bird - the leader, who has already flown along this route. However, there were cases of replacement of the leader in flight by "deputies" flying behind, as well as the merging of two wedges into one. Moreover, it was noticeable that this happened in cases when some of the birds got tired in flight and they began to fall out of order. And the conclusion was that the temporary merging of the wedges was done for the moral support of the tired. It was noticeable that the stronger birds seemed to be pushing the weaker ones into the ranks. After some time, the aligned wedges again divided into several and continued their normal flight.

And something else incredible.

In the units that provide aviation flights and control, we were armed with driving radio stations of the PAR-8 type (then more modern systems). These systems are a medium wave transmitter that emits Morse code. Moreover, the set of characters is set individually for each specific radio drive.

The antenna consisted of four parallel emitter cables located at a height on the masts. This antenna formed two radiation patterns in opposite directions, that is, two beams. And the plane that received this particular set, focusing on the maximum radiation, went to this particular drive. And during the periods of seasonal flights, in particular, cranes, we noticed every time that the flocks went straight to our drive, and then corrected the further direction of the flight.

Despite the fact that six kilometers from our small unit was located the central town, quite extensive, with three-four-story buildings, pipes and other things that could serve as a much more contrasting visual reference. It turns out that the birds caught the radiation of the drive?

It should be noted that flocks of smaller birds stopped for the night on these antenna cables. Fortunately strength allowed. And after a night's rest, the flight continued. It is possible that radio drive radiation also helped them find such an unconventional resting place in the dark. It is worth saying that there were no trees around, the area was deserted, and the high-voltage line, which was not yet connected at that time, was away from bird tracks and, apparently, did not suit them.

Some of my classmates in graduation were assigned to the fleet, in particular, to the ships of the command and measurement complex, which provide constant monitoring of space objects. Including inhabited. The guys talked about cases when flocks of birds, usually in inclement weather, found these ships in the middle of the oceans (according to the radio emission of ships?) and, in order not to die, literally stuck around their decks, equipment and superstructures. And after the weather cleared up, fed by the sailors, they resumed their flight. Preliminarily making a farewell flight around the ship. Naturally, except for those who died. Sailors of other military ships also told the same. Ornithologists consider such a flyby not a sign of gratitude, but a test of the wings and the ability of the flock to continue flying.

And until the birds are thoroughly studied, until an effective, at least in the form of a working layout, flywheel as a working copy of a bird is created, apparently, the hypotheses will remain so.

In order to correctly plot a course for the intended target, the navigator of a ship or aircraft resorts to the help of complex navigational instruments, uses maps, tables, and now GPS navigation, gps monitoring. All the more surprising in this connection seems to be the ability of birds and animals to orient themselves with amazing accuracy relative to the surface of the earth. Birds behave especially unmistakably in space. The distances that birds cover during seasonal migrations are sometimes very large. So, for example, arctic terns make a two-month flight from the Arctic to the Antarctic, covering about 17 thousand kilometers. And waders migrate from the Aleutian Islands and Alaska to the Hawaiian Islands, flying over the ocean for about 3,300 kilometers. These facts are of interest not only from the point of view of physiology. Of particular surprise is the unmistakable orientation of birds over the ocean. If during a flight over land one can assume the presence of any familiar visual landmarks, then what kind of landmarks can be encountered on a monotonous water surface?

It is also known that birds always return to their places after distant wanderings. Thus, American terns, transported 800-1200 kilometers from their nesting sites, returned to their old places, to the shores of the Gulf of Mexico, in a few days. Similar experiments have been done with other birds. The results were the same.

Not only “migratory”, but also “settled” birds have a certain ability for orientation (a trained one can return to the dovecote from a distance of 300-400 kilometers). The ability of birds to navigate in space was known in antiquity. Then they already used pigeon mail. However, by themselves, observations of the flights of birds, their behavior, practically did not give anything to clarify the reasons for orientation. Until now, there are only numerous conjectures and theories on this issue.

The English scientist Metoz empirically established that carrier pigeons orient themselves worse on cloudy days. Launched from a distance of more than 100 kilometers, they deviated by a known angle from the correct direction of flight. On a sunny day, this error was much smaller. On this basis, the opinion was put forward that birds orient themselves by the sun.

It is known that orientation by the sun in nature really exists. So, for example, some aquatic insects, sea spiders have the ability to navigate by the sun. Released into the open sea, they will unmistakably rush back to the shore - their usual habitat. When the position of the sun in the sky changes, the spiders change both the angle and direction of movement, respectively.

All these facts to some extent speak in favor of the Metosis theory. However, a significant objection to it is the night flights of many birds. True, some scientists believe that in this case the birds are guided by the stars. The so-called magnetic theory has become widespread. The idea that birds have a special, "magnetic sense" that allows them to navigate in the Earth's magnetic field, was expressed in the middle of the 19th century by Academician Midendorf. Subsequently, this theory found many adherents. However, numerous laboratory experiments, during which magnetic fields were created, in intensity many times greater than the Earth's magnetic field, did not have a visible effect on the birds.

Recently, the "magnetic theory" has been criticized by physiologists and physicists. Nevertheless, it should be noted that migratory birds show a certain sensitivity to certain special types of electromagnetic oscillations. So, for example, amateur pigeon breeders have long noted that pigeons orient themselves worse near powerful radio stations. Their statements were usually not taken seriously. But during the Second World War, numerous information was obtained about the effect on migratory birds of ultrashort waves emitted by radar installations (radar). It is curious that the radar radiation did not have a visible effect on sitting birds, even from a very close distance, but radiation directed at flying birds broke their formation.

From the point of view, a science that studies the living conditions of various animals. the ability of birds to navigate in space is quite natural. The extraordinary speed of movement and the ability to cover significant distances in a short time distinguish birds from other representatives of the living world of our planet. The search for food far from the nest undoubtedly contributed to the development of extraordinary abilities to navigate in space compared to other animals. However, as we can see, the mechanism of this interesting phenomenon has not yet been discovered. So far, we can only assume that the complex instinct of birds is not based on any one factor. Perhaps it includes elements of astronomical orientation to the sun, especially since a number of animals have this ability.

Obviously, visual orientation along the Earth's surface can also play an important role, given that the vision of birds differs in a number of features. There are, of course, some other important, yet unknown to science factors. Whether the so-called magnetic sense of birds is among them, it is not yet possible to say with certainty. Only further research with the participation of scientists of various specialties will apparently help to solve this riddle of nature.

A relatively small number of species and individuals of Anseriformes, Grebes, Anklets, Predators, Waders, Gulls, Passerines winter in the southern regions of the former USSR along the Black Sea, in the Transcaucasus, in the south of the Caspian Sea, and in some regions of Central Asia. The overwhelming majority of species and individuals of our birds winter outside the country in the British Isles and in Southern Europe, in the Mediterranean, in many parts of Africa and Asia. For example, many small birds from the European part of the former USSR (warblers, warblers, swallows, etc.) winter in South Africa, flying from wintering places up to 9-10 thousand km. The flyways of some species are even longer. Arctic terns nesting along the coasts of the Barents Sea - Sterna paradisea winter off the coast of Australia, flying only in one direction up to 16-18 thousand km. Almost the same migration path is observed for the brown-winged plover Charadrius dominica nesting in the tundra of Siberia, wintering in New Zealand, and for the spiny-tailed swifts, Hirundapus caudacutus, flying from Eastern Siberia to Australia and Tasmania (12-14 thousand km); part of the way they fly over the sea.

During migrations, birds fly at normal speeds, alternating flight with stops for rest and feeding. Autumn migrations usually take place at a slower rate than spring migrations. Small passerine birds during migrations move an average of 50-100 km per day, ducks - 100-500 km, etc. Thus, on average, birds spend relatively little time on the flight per day, sometimes only 1-2 hours However, some even small land birds, such as American tree warblers - Dendroica, migrating over the ocean, are able to fly 3-4 thousand km without stopping. for 60-70 hours of continuous flight. But such strenuous migrations have been identified only in a small number of species.

The flight altitude depends on many factors: bird species and pellet capabilities, weather, air flow speeds at different altitudes, etc. Aircraft and radar observations have shown that most species migrate at an altitude of 450-750 m; individual flocks can fly quite low above the ground. Migratory cranes, geese, waders, and pigeons were noted much less frequently at altitudes up to 1.5 km and above. In the mountains, flocks of flying shorebirds, geese, cranes were observed even at an altitude of 6-9 km above sea level (at the 9th kilometer, the oxygen content is 70% less than at sea level). Water birds (loons, grebes, auks) swim part of the flyway, and the corncrake passes on foot. Many species of birds, usually active only during the daytime, migrate at night and feed during the day (many passerines, waders, etc.), while others retain their usual daily rhythm of activity during the migration period.

In migratory birds, during the period of preparation for migration, the nature of metabolism changes, leading to the accumulation of significant fat reserves with enhanced nutrition. When oxidized, fats release almost twice as much energy as carbohydrates and proteins. Reserve fat, as needed, enters the bloodstream and is delivered to working muscles. When fats are oxidized, water is formed, which compensates for the loss of moisture during breathing. Particularly large reserves of fat are in species that are forced to fly non-stop during migration for a long time. In the already mentioned American tree warblers before flying over the sea, fat reserves can be up to 30-35% of their mass. After such a throw, the birds feed intensively, restoring their energy reserves, and again continue their flight.

The change in the nature of metabolism, which prepares the body for a flight or for wintering conditions, is provided by a combination of the internal annual rhythm of physiological processes and seasonal changes in living conditions, primarily by a change in the length of daylight hours (lengthening in spring and shortening in late summer); probably, seasonal changes in feed also play a role. In birds that have accumulated energy resources, under the influence of external stimuli (changes in the length of the day, weather, lack of food), the so-called "migratory anxiety" occurs, when the bird's behavior changes dramatically and a desire to migrate arises.

The vast majority of nomadic and migratory birds have a distinct nesting conservatism. It manifests itself in the fact that the next year breeding birds return from wintering to the place of the previous nesting and either occupy the old nest or build a new one nearby. Young birds that have reached sexual maturity return to their homeland, but more often they settle at some distance (hundreds of meters - tens of kilometers) from the place where they hatched (Fig. 63). Nesting conservatism, which is less pronounced in young birds, allows the species to populate new territories suitable for it and, providing mixing of the population, prevents inbreeding (closely related crossing). The nesting conservatism of adult birds allows them to nest in a well-known area, which makes it easier to search for food and escape from enemies. There is also the constancy of wintering places.

How birds navigate during migrations, how they choose the direction of flight, getting to a certain area for wintering and returning thousands of kilometers to their nesting site - Despite various studies, there is no answer to this question yet. Obviously, migratory birds have an innate migratory instinct that allows them to choose the desired general direction of migration. However, this innate instinct under the influence of environmental conditions, apparently, can change rapidly.

Eggs of settled English mallards have been incubated in Finland. Growing young mallards, like local ducks, flew away for wintering in autumn, and next spring a significant part of them (36 out of 66) returned to Finland in the release area and nested there. None of these birds have been found in England. Black goose are migratory. Their eggs were incubated in England, and in autumn the young birds behaved in a new place as sedentary birds. Thus, it is still impossible to explain both the desire for migration itself and the orientation during the flight only by innate reflexes. Experimental studies and field observations show that migratory birds are capable of celestial navigation: to choose the desired direction of flight according to the position of the sun, moon and stars. In cloudy weather or when the picture of the starry sky changed during experiments in the planetarium, the ability to orientate noticeably deteriorated.

From today, the day of Gerasim Grachevik, migratory birds are expected in Russia. Making long-distance flights, they return from warm countries. How are they oriented? Why are they flying like a wedge? What do they eat? We decided to answer these and other "bird" questions.

How to get directions

How not to make a mistake with the route? After all, a mistake will cost your life! But for cruise travelers this is not a problem at all: routes have long been defined and remain unchanged from year to year. Where to head, the younger generation will learn from older comrades. But what if there is only one inexperienced young in the flock? How to find out the way without a map and a gps navigator? It turns out that every bird has such a navigator, it is an innate instinct that leads the birds in the right direction. This is confirmed by cases when young individuals made their first flight absolutely independently.

Wind, wind, you are mighty!

Weather conditions certainly affect the course of migration. In warm weather, birds fly longer, and the flow of arriving birds increases dramatically. And if suddenly a severe cold snap sets in, the birds can even turn back to the south. During the autumn migration, a cold snap contributes to a faster departure. Ducks can move south without stopping, covering long distances - 150-200 km. The wind can interfere with the flight, and, conversely, contribute. Seagulls, flying rather slowly, fly in calm or with a fair wind. Naturally, with such an assistant, the flight is more intense.

Count in order!

Many birds fly in a wedge, such as cranes and geese. Some believe that birds fly like a wedge in order to cut through the air, just as the prow of a ship cuts through the waves. But it's not. The meaning of the wedge-shaped formation, however, like any other (rank, arc, oblique line), is that the birds do not fall into the vortex-like air currents created by the movements of the neighbors' wings. Due to the fact that birds in front flap their wings, additional lift is created for those flying behind. Geese thus save up to 20% of energy. At the same time, a great responsibility is assigned to the bird flying in front: it is a guide and guide for the entire flock. This is hard work: the sense organs and the nervous system are in constant tension. Therefore, the leading bird gets tired faster and is soon replaced by another.

Flight flight, and lunch on schedule!

During the flight, the flock will not always be able to fully eat - the possibilities for obtaining food are very limited. Where do you get the strength for such hard work? When going on a long journey, we tend to think about our diet in advance. So the birds prefer to eat well on the track: in preparation for the flight, they eat very tightly in order to accumulate more fat reserves for a long flight.

Rest time, and flight hour

The flight is difficult, and the supply of energy quickly dries up, so it is very important for the birds to recuperate. Some species of birds fly almost without rest: a woodcock, for example, covers a distance of up to 500 km in one night without stopping. Others cannot boast of such endurance and make many stops. As a rule, the speed of these birds is small. They arrange a rest for themselves near the reservoirs, where they can recuperate, refresh themselves and quench their thirst. It takes a lot of time, and on average it takes about an hour to fly a day.

Wandering in the dark

Many birds migrate at night. Quails, coots and woodcocks, for example, fly only at night. Moreover, not only nocturnal birds fly at night: wild geese, loons and many species of ducks continue their journey at any time of the day. But how do birds fly at night, accustomed to daylight? The fact is that birds can navigate by the stars, the sun and the outlines of the landscape. They also easily determine their location by the Earth's magnetic field, so they can move in conditions of very poor and even zero visibility.

9. Orientation of birds according to the sun

In the history of science, it is not uncommon for a researcher, striving for one result, to obtain another, sometimes much more important one. However, it also happens that a scientist finds a brilliant solution to exactly the problem that he set himself, and at the same time discovers that the causes of the phenomenon under study are much deeper than he expected.

It was in this way that Cramer made his discovery, after which many biologists at various research centers abandoned their current work to join those who struggled to solve the riddle of the living clock.

Gustav Kramer was born in Mannheim in 1910 and received his biological education at the Universities of Freiburg and Berlin. His first scientific work in the field of physiology of the lower vertebrates was so promising that at the age of twenty-seven he was appointed head of the department of physiology of the Naples Zoological Station.

He began his world-renowned research on the orientation of birds in flight at the University of Heidelberg and continued at the Institute of Marine Biology. Max Planck in Wilhelmshaven, located on the west coast of the cold North Sea. Watching seabirds fly swiftly to nesting grounds, Cramer pondered the age-old mystery of flight, the marvelous precision with which migratory birds find their way to a distant destination.

Rice. 30. Exceptional flight route for the arctic tern.

He marveled at the heroism of the arctic tern, that extraordinary flyer that nests one and a half hundred kilometers from the North Pole, and with the onset of autumn flies over Canada, then over the lifeless expanses of the Atlantic Ocean to the western shores of Africa and, having rounded the Cape of Good Hope, remains to winter south of Port Elizabeth.

But the Arctic tern is not the only example of excellence in the art of navigation. The New Zealand bronze cuckoo covers a distance of two thousand kilometers, flying across the Tasman Sea to Australia, and from there another fifteen hundred kilometers north across the Coral Sea to its tiny wintering grounds in the Bismarck Archipelago and the Solomon Islands. It is even more surprising that a young cuckoo, making such a flight for the first time, can do it alone, ahead of her parents by at least a month.

Ringed white-headed zonotrichia returns year after year to the same bush in the garden of Professor L. Menwald in San Jose (California), flying three and a half thousand kilometers from their nesting sites in Alaska.

The mystery of such precisely targeted flights has long been of interest to biologists, and they have explained it in different ways. And it is not surprising: the problem was extremely complex, and there were no opportunities to scientifically develop it at that time.

Therefore, when Cramer reported to the International Congress of Ornithologists on the results of his experiments on the study of the orientation of birds, the Congress was amazed and delighted. R. Peterson said: "Gustav Kramer's report on experiments with starlings, which showed that the only source of orientation for birds is the sun, is extremely exciting and captivating."

The field of study of animal migration is very broad, and determining the direction of migration is, of course, only one of its aspects. But penetration into one aspect often leads to clarification of the whole problem as a whole.

As we have seen, animals often migrate to very remote places and there they find the final, sometimes negligible goal of their flight. Such accuracy would be physically impossible in the absence of some kind of control system, similar to the control system of a homing torpedo.

At the same time, it is extremely important to understand that such a control system cannot function without a constant influx of information from the outside world. A homing torpedo must receive signals that bounce off the target or it will miss. Similarly, animals must receive signals from the environment, otherwise the mechanism that guides them will not work.

But what are the signals? Information coming from the environment can be perceived either by the bird's sense organs known to us, or not yet known. At the same time, regardless of how this information is perceived, it must be such that the bird can solve three problems.

First, where it is at the moment and in what direction it needs to go further.

Thirdly, how to find out the destination when you arrive there.

Is there any single sense, known or unknown to us, through which the bird could receive an answer to all these questions? Let's try to consider the possible types of information.

Every object on the Earth's surface radiates heat. Hot objects emit high-intensity, short-wavelength radiation, while cold objects emit low-intensity, long-wavelength radiation. Therefore, both the frequency and intensity of radiation at the poles will differ greatly from those near the equator. One might assume that long-distance migrants pick up on this difference. But, as Griffin noted, this would be too simple an explanation for the ability of birds to navigate.

Three facts contradict this explanation. Radiation propagates in a straight line. Therefore, the radiation from an object located only one and a half hundred kilometers from the bird will fall to a point located much higher than the level of ordinary bird flights. In addition, thermal radiation is strongly distorted by such features of the landscape as forests, lakes, deserts, cities, which introduce the so-called "noise" into it. Finally, no one has so far convincingly proved that birds can perceive changes in thermal radiation.

All this applies to ordinary thermal radiation. But what about something less obvious? With the Earth's magnetic field, for example. It has also been named as a possible "compass" for birds. The equipotential lines of the Earth's magnetic field approximately coincide with the parallels. If the bird feels the difference in the magnetic field strength, then it can determine the geographical latitude of its location. Or, say, magnetic inclination. If the bird perceives it, the arrow of its "compass" will be in a horizontal position above the equator and almost vertical - at the poles. Changing the position of this arrow will tell the bird where it is. But even here there are obstacles. Experiments have shown that birds do not react to a magnetic field, even much stronger than the Earth's magnetic field. In addition, experimenters have never been able to teach birds to respond to magnetic fields.

What other features of the bird's environment can give it information about its location? Obviously the rotation of the earth. The angular velocity of its rotation is such that a point on the surface of the Earth, located near the equator, moves at a speed of about 1600 km / h. If a bird is flying east at a speed of 100 km/h, its true speed (relative to the sun) will be about 1700 km/h, and if it is flying west, then about 1500 km/h. If the bird perceives this difference, then it can apparently determine the direction of flight and the geographical latitude of its location.

What if the bird doesn't fly? A case is known when geese with clipped wings traveled several kilometers in the direction of their usual flights. In addition, it has been convincingly shown that caged birds are excellent at determining direction. But, despite the evidence of the facts, scientists still have not been able to establish what helps birds navigate in flight.

So we've got some idea of ​​the complexity of the problem Cramer is facing. A considerable difficulty in experiments on the study of the orientation of birds was the determination of the direction of their flight, since it could be observed only by following the birds. A new experimental method was needed.

It has long been known that during the migratory season, birds kept in cages show what is known as "migratory restlessness": they flit from place to place, but at the same time maintain a certain direction. Isn't that the direction they would take to fly if they were free? Kramer decided to answer this question.

He chose the European starling as an object for his observations, which perfectly tolerates keeping in cages, is easily tamed and can be trained.

And soon the laboratory in Wilhelmshaven acquired young yellow-mouthed birds, and Kramer impatiently waited for the end of summer, when autumn flights begin.

Even before the onset of cool October days, he established a continuous observation of his starlings during daylight hours (since the flight of starlings takes place during the day). From Wilhelmshaven, starlings usually head southwest in autumn. Would caged starlings prefer this direction? Cramer did not have long to wait: in October, his birds thrashed nervously in the southwest corners of their cages.

What landmarks did the birds use? Maybe some purely physical feature of the terrain, like a tree or a hill? Cramer placed the cages in various places, covering the bottom of the cages so that the starling could see only the sky, but the birds still stubbornly rushed to the southwest. The next spring, when the starlings' flight direction changed to the northwest, the birds in their cages preferred the northwest direction.

This is the essence of the experimental method that Kramer has been looking for for so long. Now he had to create equipment to make thousands of observations and process them statistically.

A round cage was built with an absolutely symmetrical inner surface: the bird in it had no landmarks by which it could determine the direction. From a perch located in the center of the cage, during the period of migratory disturbance, the bird constantly fluttered up, trying to fly all the time in one direction. The transparent plastic floor allowed an observer lying under the cage to follow the bird. To ensure an accurate record of the position of the bird at any given moment, the plastic was marked up into a number of sectors.

The most important variable in Cramer's experiments was the direction of the light entering the cell. Therefore, he placed the experimental round cage in a six-sided pavilion, each side of which had a shuttered window. A mirror was attached to the inside of the shutter, which changed the direction of the beam of light entering the cage. And finally, both the cage and the screen around the pavilion could be rotated.

When everything was ready, Kramer settled down under the transparent bottom of the cage with a notebook and a pencil in his hands and every ten seconds recorded which of the marked sectors the bird occupied. In the morning for at least an hour, Cramer noted the bird's position and very soon became convinced that neither the equipment nor his own presence disturbed the starlings.

Now the researchers were no longer hindered by the uncertainties and inaccuracies that are inevitable when observing in the field. The laboratory experience allowed the experimenter to change the controlled conditions in any way he wanted. How, for example, will birds behave if a beam of light entering a cage is reflected by a mirror at right angles to its natural direction? Indeed, in such a situation, the position of the sun should seem to be rotated by 90 ° to the caged bird.

Rice. 32. A starling trained to fly in the same direction at the same time (for example, when the sun's rays fell in the direction indicated by a light arrow) knew which direction to fly at any other time of the day (for example, when the sun's rays fell in the direction of the dark arrow). The dots show the individual positions of the bird.

Once again, Kramer pedantically wrote: “For the first 10 seconds, the bird is in sector 8; the second 10 seconds - in sector No. 9; the third 10 seconds - in sector No. 7; the fourth 10 seconds - in sector No. 9; fifth 10 seconds - in sector number 8 ... "and so on, until he made more than 350 entries in just an hour. Soon the validity of the results obtained became apparent. But will skeptical scientists accept them? Certainly not, since a completely startling conclusion followed from these results. And Kramer again takes up his tiresome observations.

When he announced his findings, the scientific world was truly amazed. What surprised scientists the most was the fact that when the direction of the sun's rays was changed by 90°, the starlings tried to fly in a new direction, rotated by the same 90°. So, to determine the direction of the flight, the birds need to take a bearing to the sun!

Cramer was looking for an answer to his questions, changing the conditions of his experiment in every possible way. Rotated an opaque screen around the pavilion so that the birds could only see part of the sky. Rotate the cell. He covered the pavilion with screens to vary the amount of light penetrating into it, simulating varying degrees of cloudiness. But no matter how he changed the conditions, the starlings always chose the right direction if they saw the sun directly.

Cramer, of course, was familiar with Behling's early work, which showed that bees could be taught to look for food in a certain direction. But what if you try to train birds in the same way?

The researcher builds a round training cage, which, like the first one, looks absolutely symmetrical from the inside. But outside around the cage, he evenly placed twelve completely identical feeders, covered with rubber membranes with slots. Until the bird stuck its beak through the slot, it did not know which of the feeders contained the grain.

Now Kramer needed to train the bird to look for food in one side of the cage. He chose an oriental feeder for this and poured grain into it at seven o'clock in the morning. The bird showed great perseverance and after a series of attempts found that the food was only in the eastern feeder. After 28 days of training (training took place from 7 to 8 in the morning), the starling learned his lesson.

The time has come for a decisive test. Kramer moved the cage ten kilometers and at 17.45 poured grain into the eastern feeder. How will the bird behave now?

During the morning training, the sun was slightly to the right of the eastern feeder. Now, by the end of the day, it was behind the western one. Will the bird still look for food in the eastern feeder or turn after it in the direction of the sun? Kramer waited tensely. The starling darted around the cage a little, apparently in indecision, and then, making a mistake only once, turned to the eastern feeder.

So the bird somehow knew that in order to find the east in the morning, it was necessary to move towards the sun, and at the end of the day - so that the sun was directly behind!

To further confirm his conclusions, Cramer came up with an extremely elegant experiment. First of all, he trained the starling to find food regardless of the time of day in a western feeder. Then he covered the cage with a protective screen from the real sun and illuminated it with an artificial sun, but in such a way that the light fell all the time from the same side- from the west.

Rice. Fig. 33. Cramer's installation for studying the choice of direction by a starling at a fixed position of the "sun" (C) (above). First, the starling was trained to search for food in the open sky (a) in a feeder (P) located in the western sector of the cage (K). Then they blocked the cage with a protective screen (E) from the real sun and turned on the fixed "sun". And the bird, taking the artificial “sun” for the real one, looked for food in the eastern feeder in the morning (b), in the northern one at noon (c) and in the western one at the end of the day (d).

What will the poor bird do with such a "sun" that shines continuously from the same side? To the surprise of Cramer, who was burning with impatience, the starling treated this luminary as if it were a real one, that is, he behaved as if the "sun" was moving, as it should be, across the sky. Since he was trained to look for food at any time of the day in a western feeder, he looked for it in east feeder at 6 o'clock in the morning, in the north - at noon and in the west - at 17 o'clock.

Could it now be doubted that this bird with dark iridescent feathers could determine the time of day to the nearest minute?

These are the amazing discoveries Cramer reported to the scientific world in the early 1950s. And although these discoveries very quickly brought him world fame, he himself looked at his achievements through the eyes of an open-minded person. There was still a lot to be done to find out exactly how the birds orient themselves.

Since he showed that the bird determines its direction by orienting itself to the sun and taking into account its daily movement, it could be considered that it possesses a solar compass, which it uses in the same way as a navigator uses a magnetic compass to plot a course. But this was only a partial solution to the problem. After all, in order to determine the direction, a person must also have a map, and also know his location on this map. This means that in order to achieve the ultimate goal of the flight, the bird also needs to have some kind of map. But no one knew about such a map yet. And Kramer turns to literature. One of the English researchers, Geoffrey Matthews, studied the behavior of carrier pigeons for a long time and after that wrote a lengthy monograph on the navigation of birds. She interested Cramer, who very soon realized how much the experimental technique developed by Matthews promised him. Matthews released carrier pigeons, previously carried away from the dovecote to a specially chosen place for this (open plains with equal visibility in all directions), and followed the direction of their flight through binoculars until the bird was out of sight. These observations were carefully compared with the timing of the return of birds to the nest.

Given the results of Matthews, Cramer outlined a broad program of his own experiments, which, unfortunately, he could not carry out.

In search of well-guided birds, he began to catch wild pigeons in the mountains of Calabria, in southern Italy. On April 4, 1959, during one of the ascents, he fell and died.

Gustav Cramer proved indisputably that birds are able to navigate by the position of the Sun in the sky, correcting for its movement. And all this was explained in the only way - birds have their own clock. Moreover, they are so accurate that they can only be compared with a chronometer used by navigators.

Rice. 34. Gustav Kramer releases carrier pigeons from the tower of the old Heidelberg castle near Hesse.

What to feed the birds! With such a question, I was often approached by phone or in person, both by acquaintances and by complete strangers. It happens that some bird flew into the apartment or you picked up a frail chick that fell out of the nest, or even took adults under your care