Birds and sky. Features of orientation of migratory birds. How do migratory birds navigate? How do migratory birds navigate?

A relatively small number of species and individuals of Anseriformes, grebes, great-creepers, raptors, waders, gulls, and passerines winter in the southern regions of the former USSR along the shores of the Black Sea, in Transcaucasia, in the south of the Caspian Sea, and in some areas of Central Asia. The vast majority of our bird species and individuals winter outside the country in the British Isles and Southern Europe, the Mediterranean, and many areas of Africa and Asia. For example, many small birds from the European part of the former USSR winter in South Africa (warblers, warblers, swallows, etc.), flying up to 9-10 thousand km from their wintering grounds. The flight paths of some species are even longer. Arctic terns, Sterna paradisea, nesting along the coasts of the Barents Sea spend the winter off the coast of Australia, flying up to 16-18 thousand km in one direction only. The flight path is almost the same for brown-winged plovers, Charadrius dominica, nesting in the tundra of Siberia, wintering in New Zealand, and for 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 migration, birds fly at normal speeds, alternating flights with stops for rest and feeding. Autumn migrations usually occur at a slower rate than spring migrations. During migration, small passerine birds move on average 50-100 km per day, ducks - 100-500 km, etc. Thus, on average per day, birds spend a relatively short time on migration, sometimes only 1-2 hours However, some even small land birds, for example, 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 intense migrations have been identified only in a small number of species.

Flight altitude depends on many factors: the type of bird and pellet capabilities, weather, speed of air flows at different altitudes, etc. Observations from airplanes and using radars have established that migrations of most species take place at an altitude of 450-750 m; individual flocks can fly very low above the ground. Migrating cranes, geese, waders, and pigeons were observed much less frequently at altitudes of 1.5 km and higher. In the mountains, flocks of flying waders, geese, and 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 walks. Many species of birds, usually active only during the day, migrate at night and feed during the day (many passerines, waders, etc.), while others maintain the 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 increased nutrition. When oxidized, fats release almost twice as much energy as carbohydrates and proteins. Reserve fat enters the bloodstream as needed and is delivered to working muscles. The oxidation of fats produces water, which compensates for the loss of moisture during respiration. Fat reserves are especially large in species that are forced to fly non-stop for long periods of time during migration. In the already mentioned American tree warblers, before flying over the sea, fat reserves can amount to up to 30-35% of their mass. After such a throw, the birds feed intensively, restoring energy reserves, and again continue their flight.

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

The overwhelming majority of nomadic and migratory birds have clearly expressed nest conservatism. It manifests itself in the fact that the breeding birds return from wintering to the previous nesting site the next year 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). Less clearly expressed nesting conservatism in young birds allows the species to populate new territories suitable for it and, by ensuring mixing of the population, prevents inbreeding (inbreeding). The nesting conservatism of adult birds allows them to nest in a well-known area, which makes it easier both to search for food and to escape from enemies. There is also constancy of wintering places.

How do birds navigate during migration, how do they choose the direction of flight, arriving in a certain area for the winter 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 can apparently change quickly under the influence of environmental conditions.

The eggs of resident English mallards were incubated in Finland. The grown young mallards, like local ducks, flew away for the winter in the fall, and the following spring a significant part of them (36 out of 66) returned to Finland to the release area and nested there. None of these birds have been found in England. Black geese are migratory. Their eggs were incubated in England, and the young birds behaved like sedentary birds in the new place in the fall. Thus, it is not yet possible to explain both the desire to migrate and orientation during the flight only by innate reflexes. Experimental studies and field observations indicate that migrating birds are capable of celestial navigation: choosing the desired flight direction based on 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 navigate noticeably deteriorated.

Undoubtedly, instinct, that is, the innate, inherited ability for certain behavior, is of great importance in flights. An example of instinct in birds: no one teaches a bird to build a nest, but when it first begins to build it, it does it in the same way as all birds of its species. In some birds, young birds fly away first, and then older birds. Consequently, no one shows the young people the way to wintering; they somehow “know” it themselves from birth.

Many experiments confirm that it is “instinct” that guides birds.

During one of these experiments, a group of storks were taken from their nests shortly before the time of autumn migration and moved to another place. From this new location they had to fly in a different direction to reach their winter quarters. But when the time came, they flew in the same direction in which they had flown from their old place!

Even if the birds were taken hundreds of kilometers away from their native places by plane, when they were released, they flew exactly to their home.

In another experiment, the scientist took duck eggs from England to Finland, and there they hatched into ducklings. But it must be said that wild ducks living in England lead a sedentary lifestyle, and ducks from Finland fly to the west of the Mediterranean Sea in winter.

The experiment showed an unexpected result. After the “Finnish” ducks flew south, the ducks hatched from the “English” eggs also took to the sky. The ringed birds flew over the same regions that the ducks from Finland usually crossed and reached the wintering grounds of their foster parents. The following year, most of these ducks returned to Finland.

How do birds navigate their way? We must admit that we don’t fully know this yet.

One hypothesis is that birds sense the magnetic fields that surround the Earth. Magnetic lines are located in the direction from the north magnetic pole to the south. Perhaps it is these lines that serve as guides for birds.

Scientists conducted experiments: magnetic plates were hung on the necks of pigeons. This made it difficult for the birds to navigate, but the magnetic plates could not completely lead them astray.

Additional landmarks for determining the direction of flight are landscape features (turn of a river, mountain, group of trees). It is possible that birds also navigate by the location of the sun. During long-distance flights, the most important, apparently, are not terrestrial, but celestial landmarks: the sun during the day, the moon and stars at night.

Most likely, birds during migration use all these types of landmarks: magnetic field, astronomical and terrestrial landmarks.

One of the most amazing and mysterious abilities of birds is migration. Every year they gather in flocks and travel thousands of kilometers to wait out the cold in a more favorable climate and never make a mistake in the chosen path.

Why do birds travel?

The main reason for the flight is lack of food. During the cold season, it is difficult to obtain insects, fruits or seeds in the required quantities. But further south, they are in abundance. Some birds cannot survive the long flight and die, but most survive and return warm.

To survive a long journey, the bird must have good health, a significant fat reserve, which is the only source of energy during the journey, and new plumage. Therefore, immediately after the chicks have grown up, they are engaged in their renewal and preparation.

So how do birds navigate in space?

It is known that birds always return to their old home, and this applies not only to migratory birds. Pigeons, for example, do not fly away for the winter, but they navigate the terrain just as well and can find their home at a distance of more than 100 km. Until recently, ornithologists believed that birds were driven by instinct and the ability to navigate by the sun and stars. But recent research indicates that birds sense the earth's magnetic field, the lines of which are located in the direction from north to south and serve as guides.


Birds are helped to detect the magnetic field by special crystals located on the bridge of the nose - magnetites; they perceive information like a compass. This helps the bird determine not only the direction of flight, but also its current location. There are still many questions left on the issue of geomagnetic orientation and solutions to them cannot yet be found in any book, but scientists do not give up and, not paying attention to the opinions of skeptics, continue their research.

From today, the day of Gerasim Grachevik, migratory birds are expected in Russia. Making long-distance flights, they return from warm countries. How do they navigate? Why do they fly 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 winged travelers this is not a problem at all: the routes have long been determined and remain unchanged from year to year. The younger generation learns where to head from their older comrades. But what if there is only one inexperienced youngster left in the flock? How to find out the road without a map and GPS navigator? It turns out that every bird has such a navigator; it is an innate instinct that leads birds in the right direction. This is confirmed by cases when young individuals made their first flight completely independently.

Wind, wind, you are powerful!

Weather conditions certainly influence the course of migration. In warm weather, birds fly longer and the flow of arriving birds increases dramatically. And if suddenly there is a strong cold snap, the birds may even turn back to the south. During the autumn migration, colder temperatures promote faster departure. Ducks can move south without stopping, covering long distances - 150-200 km. The wind can interfere with the flight, and, on the contrary, facilitate it. Seagulls, flying rather slowly, fly in a calm or with a tailwind. Naturally, with such an assistant, the flight is more intense.

Pay in order!

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

The flight is a flight, and lunch is on schedule!

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

I have time to rest, but the flight takes an hour

Flight is a difficult task, and energy reserves quickly deplete, so it is very important for birds to recuperate. Some species of birds fly practically without rest: woodcock, for example, covers a distance of up to 500 km without stopping in one night. Others cannot boast of such endurance and make many stops. As a rule, the speed of these birds is low. They arrange a rest near ponds, where they can recuperate, refresh themselves and quench their thirst. This takes a lot of time, and the flight takes about an hour on average per 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 migrate at night: wild geese, loons and many species of ducks continue their journey at any time of the day. But how do birds, accustomed to daylight, fly at night? The fact is that birds can navigate by the stars, the sun and the contours of the landscape. They also easily determine their location using the Earth’s magnetic field, so they can move in conditions of very poor or even zero visibility.

The book is devoted to one of the most interesting and mysterious problems of ornithology - the problem of loyalty of migratory birds to their homeland and home. The feeling of “home loyalty” is inherent in a wide variety of animals - from insects to primates, including humans. This feeling has an instinctive basis and manifests itself in the individual in the desire to return home - to a place familiar to it after a temporary absence. For migratory birds, “home” can mean a place of birth, nesting, or wintering.

For readers interested in problems of biology and ornithology, as well as for nature lovers.

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During migration, birds travel vast distances to reach wintering or nesting areas, often located on another continent. How birds manage to find the right path in the most difficult conditions, when they are constantly blown off course by the wind, at night, often when it is completely cloudy, when neither the stars nor the earth is visible, is difficult to imagine. But they find it, even when they are young and inexperienced. At first they thought that the young were flying with adult birds that showed them the way. As an example of “family” flights, flocks of swans, geese or storks, consisting of parents and children, which often stay together not only during autumn migration, but also during the winter until the nesting season, were usually cited. Special experiments were required to detain young birds in the nesting area to prove that young birds are able to independently find the right path to wintering. Such experiments were carried out by E. Schutz with white storks. He caught young storks from the eastern population, from which the birds usually fly to Africa for the winter in a south-easterly direction, skirting the Mediterranean Sea from the east, and released them, after the adult birds had flown away, in the western part of Germany, from where the storks fly south-west way. As the findings of ringed storks showed, in the same year the young ones flew in their southeastern route, which is innate for them.

Rice. 33. Results of an experiment on the introduction of young and adult common starlings from the autumn migration route from Holland to Switzerland.

Light circles are where adult birds were found after release, dark circles are where young birds were found.

Thin arrows indicate the direction of bird importation; light and dark arrows - the direction of movement of adult and young birds after release.

Later, A. Perdek, in the late 50s, transported about 15 thousand starlings during the autumn migration from Holland to Switzerland and Spain. In the first experiment, he released 11 thousand starlings in three places in Switzerland (750 km southeast of the capture site). In the same year, 354 returns were received, 131 of them from distances greater than 50 km. from the place of release. These findings of displaced starlings showed that young birds that were migrating for the first time continued to fly after release in the standard direction for European populations of this species - to the west and southwest (Fig. 33). As a result, they spent the winter in an unusual area for them (in Southern France and Spain). Returns in subsequent years showed that the birds continued to return to these areas in the future. Adult birds showed a double distribution after release: one group continued to fly like young birds, but the other returned from their typical wintering areas (England and northern France). The third group (19 individuals) returned from the northern regions, from the traditional migration route of starlings. In the next experiment, 3600 starlings, captured in the fall in Holland, were transported to Barcelona (Spain). Again, young birds continued to migrate in a compass southwesterly direction, while adults moved towards the wintering area.

Based on these data, Perdek came to the conclusion that young birds on their first migration adhere to their innate direction, while adults navigate to the place where they have wintered before. Based on this assumption, it was interesting to find out how the first-year birds would behave after the displacement in the spring, since they should already know, like the adults, where their nesting area is located.

Perdek conducted such an experiment. About 3 thousand young starlings caught in Holland were released in Switzerland in February and March. That same year, some of the birds were found in their nesting area, as would be expected. However, some birds remained to nest in the release area, and some of these birds returned here to nest in subsequent years. This suggests that in some cases, the primary information about the nesting area received by the bird as a juvenile may be “blocked” by other, later information about the new nesting site. How do young birds find their wintering area during their first migration? Various hypotheses have been put forward: 1) that birds have an innate knowledge of wintering locations, 2) that they fly in the direction of wintering grounds until they have used up all the energy “intended” for migration, 3) that they are guided by changes in the ratio of day and night lengths (photoperiod) and biological clock for the timely completion of migration and even 4) that they use the temperature gradient, that is, they fly in the direction of rising temperatures in the fall. None of these assumptions have been confirmed in experiments. Currently, the most proven hypothesis is the “endogenous temporal control” of migration, put forward by P. Gwinner and E. Berthold. According to this hypothesis, the duration of migration in birds, as well as the direction, is innate, i.e., during the first migration, the bird flies for a strictly defined time, maintaining a standard direction, as a result of which it ends up in the area where the wintering of the species is located, even if she is on another continent. It seems incredible that in this way you can get, for example, from Siberia to a small area in Africa, but nevertheless, this is so far the only method that has experimental confirmation. Numerous experiments testing the duration of migratory restlessness in caged conditions in captive-bred birds of different species and populations have provided evidence that the level and duration of migratory activity is innate and specific to the species, population, and even to different individuals from the same population.

Recently, G. Bibach showed in experiments on the hybridization of migrating and sedentary individuals of the Robin that in the group of descendants from migrant parents, more individuals with migratory activity were born (89%) than in the group of descendants from sedentary parents (53%). Similar data were obtained for the Black-headed Warbler. Thus, it was established that even the phenomenon of partial migration in a population is controlled genetically.

Comparing the duration of the migratory state in autumn in young and adult finches and common finches in laboratory conditions, I found that in young individuals a decrease in fat reserves and migratory activity occurs at strictly defined times, when migration in these species in nature begins, while in In adult individuals, the end of the migratory state in captivity is delayed by approximately 10–14 days. (Fig. 34). This is due to the fact that in young birds the first migratory state is controlled only by an innate endogenous program, and therefore ends on time in captivity. In order for an adult bird to finally stop migrating, it needs to receive information that it has reached its wintering place. In cellular conditions, it naturally cannot obtain this information. In the spring, the end of the finch’s migratory state is delayed for both adults and first-year birds if they are delayed on the migration route, but it is completed on time, as M.E. Shumakov and N.V. Vinogradova showed, if the birds are kept in their nesting area.

Rice. 34. The timing of the end of the migratory state in young (1) and adult (2) common lentils (A) and finches (B) detained during autumn migration on the Curonian Spit.

Later, E. Ketterson and V. Nolan, recording in the fall the intensity of night migratory activity and fat deposition in three groups of juncos in the state of Indiana (USA), within the wintering range of this species, found that in the group consisting of birds that had wintered here in the past years, fat deposition and night activity were significantly lower than in the other two groups, which included birds brought to the study area from Canada, from nesting sites. In the spring experiments, there were no noticeable differences in these indicators among all three groups. The authors concluded that the presence of birds in familiar wintering grounds before the start of autumn migration can suppress the development of the migratory state.

In another experiment, the researchers analyzed the factors that determine the end of spring migration in previously breeding indigo buntings. For this purpose, they captured 46 adult males during the nesting period, 22 of them in their individual territories. Until the end of the postnuptial molt, the birds were kept in an open enclosure directly in the area of ​​capture, after which they were transferred to a closed aviary, where a photoperiod was automatically maintained corresponding to the migration and wintering areas of this species. Before the start of spring migration, 22 males captured in individual territories were divided into two equal groups. One group (experimental) of birds was released directly on their last year's nesting sites, the other (control) was transported and released the next day 1000 km away. south of the study area. The remaining 24 males were placed in cages (where the birds' motor activity was recorded) located in a pavilion with a natural photoperiod, but excluding the view of the surrounding area. The pavilion itself was located directly in the area where the birds were caught during nesting. After all these operations, a series of control catches of males that had begun nesting in the study area was carried out. From the experimental group, 4 males were caught, and on their previous year's nesting sites. From the control group, brought 1000 km away, 5 males were caught. At the same time, birds kept in cages showed nocturnal migratory restlessness, despite the fact that they were in their nesting area.

The authors of this interesting experiment came to the conclusion that indigo buntings need to go directly to the nesting territory they had previously imprinted to stop their spring migration. If birds are released into this territory before the start of spring migration, then the development of the migratory state, despite its endogenous program, is blocked (control group). If the birds are kept indoors in their nesting area, their migratory state develops normally. It is possible that birds, being indoors, simply cannot determine the coordinates of their location; for this they need to have freedom of movement within a certain territory, similar to how they do when imprinting the future nesting area (see Chapter 5). However, it is clear from both our and these experiments that the end time of spring and autumn migration in adult birds is primarily determined by whether they have reached a familiar nesting area (wintering area) or not.

Recently, facts have emerged indicating that not only the overall duration of migration is genetically programmed, but also its strategy on different sections of the route. Gwinner and Berthold found that long-distance migrants (warblers and warblers) exhibited the most intense nocturnal activity in caged conditions in autumn when their free-ranging conspecifics were crossing the Mediterranean and the Sahara at maximum speed. Then the migratory restlessness of the caged birds gradually decreases, just as the free birds also reduce their flight speed. This coincidence led them to believe that the timing of the first autumn migration in these species is determined, at least in part, by an endogenous innate program.

The innate program determines not only the duration of migration in birds, but also its direction. V. Neuzser tested the direction of migratory activity in round Emlen cells of captive-fed warblers from two populations - from Germany, migrating to the southwest in the fall, and from Austria, migrating to the southeast. Significant differences in the orientation of these groups of birds were obtained (241° for birds from Germany and 185° for birds from Austria), corresponding to the innate directions of migration of these populations. However, many migratory birds will not reach their wintering grounds if they fly in only one standard direction. For example, European birds wintering in Africa first fly southwest, as shown by findings of ringed birds, and then turn south or southeast in France or Spain.

Rice. 35. Changes in the direction of autumn migration and orientation in a round cage in young garden warblers raised in captivity in Germany.

The shaded part of Africa is the wintering area of ​​this species.

The question arises, how do young birds migrating for the first time determine when it is time for them to change direction of flight? It turned out that even such information is in the genetic program. Checking the migratory direction of young garden warblers raised in captivity in round cages throughout the fall, Gwinner found that in August-September the birds choose the southwestern direction, and in October-December - the southeastern direction (Fig. 35). Further experiments with reared warblers showed that a change in the direction of jumps in birds in a round cage was observed even when the birds could not see the sky. Gwinner and Wiltchko suggested that the change in orientation occurs according to the Earth's magnetic field.

It has now been proven that birds use the Earth's magnetic field to choose the direction of migration in the first autumn. V. and R. Viltchko showed on several species (robin, garden warbler, pied flycatcher, etc.) that the ability to determine the migratory direction is formed without astronomical information, on the basis of a magnetic compass - the main mechanism for implementing a genetically fixed migratory direction. Moreover, birds are oriented not by the poles of the Earth’s magnetic field, but by the direction of declination: north for a bird is where the angle between the magnetic inclination and the gravity vector is smaller. A magnetic compass of this kind is only suitable within one hemisphere. It will not act at the equator, but beyond the equator it will give the opposite direction. According to V. Viltchko, an astronomical compass is adjusted using a magnetic compass. The stellar compass, the existence of which was proven by S. Emlen, and the rotation of the firmament are used, according to Wiltchko, only by night migrants during flights. The solar compass, which includes determining direction by sunset, is also an additional orientation system, which is adjusted in the first months of the bird’s life according to the primary, i.e. magnetic, system. Wiltschko believes that the role of the solar compass in migration orientation is currently overestimated.

Other researchers disagree with this point of view. In particular, K. Able believes that the solar compass develops in migratory birds independently of the magnetic one. The star compass is also formed independently by sighting the axis of rotation of the star sphere. The polar point provides a reference direction relative to which the innate azimuth of migration is realized. F. Moor, E. B. Katz and other researchers prove that direction determination by migratory birds occurs mainly by the sun during sunset. The stars are used only to maintain this direction. Further research will show which of these points of view is more correct.

The direction of flight of birds during migration can be influenced by other factors: wind, landmarks, magnetic anomalies, etc. Can birds adjust their path after exposure to such factors? P. Evans analyzed the autumn course of nocturnal migrants of Scandinavian origin, who leave Norway in a south-south-west direction, passing through southern England and western France. If the birds are caught in strong easterly winds while crossing the North Sea, they could be blown away and travel along the north-east coast of Britain. Do the birds continue to migrate in the standard direction, or do they reorient to the south or southeast to reach the normal migration route? Evans checked the orientation of the off-course birds caught by the North Yorkshire in round cages. In these experiments, many birds showed a southern and southeastern orientation, i.e., they tried to compensate for the displacement. Evans later compared autumn and winter finds of common redstarts and pied flycatchers banded north of Yorkshire with those collected on the coast south of Yorkshire. Returns from displaced birds showed the same geographic distribution as undisplaced birds. Evans concluded that these two species have the ability to correct displacement.

Radar observations indicate that flying birds compensate for about? - ? the influence of wind on migratory flight by changing speed. Calculations by G. Klein showed that for the long-distance migrant, the garden warbler, the maximum displacement reaches 900 km, which is only 1/10 of the migration distance for extremely long-distance migrants, while for the black-headed warbler (short-range migrant) such an error is about a third of the distance, provided that birds half compensate for the influence of the wind. Perhaps for this reason, Klein suggests, short-haul migrants avoid migrating in stormy weather, as this can lead to large errors in migratory distance.

There is evidence that during autumn migration, young birds have a greater range of directions than adult birds. In particular, F. Moore discovered this in savannah buntings when comparing orientation behavior in Emlen cells in young and adult birds in North Dakota. He suggested that differences in orientation between adult and juvenile birds reflected the importance of migratory experience. Young people can make more orientation mistakes; they do not have information about the final goal of migration. Moreover, adult birds may know some parts of the route where they stopped during the previous migration.

The third chapter shows that some species of birds, in particular waterfowl, have permanent stopping places along the migration route, which they know and use annually for rest and restoration of fat reserves. There may be several such places on the route. Therefore, it is quite possible that adult birds with migration experience use a different strategy than is usually assumed for migrating from breeding areas to wintering areas and vice versa.

Rice. 36. Hypothetical scheme of “stage-by-stage” migration of migratory birds during the first and subsequent flights between breeding and wintering areas.

1 - nesting area (purpose of spring migration), 2 - wintering area (purpose of autumn migration), 3 - main stopping places for birds during migration (intermediate purposes of autumn and spring migrations), 4 - random stopping place during migration (not the purpose of migration ).

The solid line is the path of the first autumn and spring migrations, the broken line is the path of the subsequent migration of an adult bird.

I think that birds, primarily waterfowl, can carry out a “step-by-step” migration strategy, which consists in the fact that birds fly from one familiar place on the route to another and so on until the final goal (Fig. 36). If for some reason they go off course (for example, they are blown away by the wind), then they try to go to the nearest point on the route that they are familiar with. There are facts that displaced birds (see the description of A. Perdek’s experiments) tend to go to the area on the route where their migration path was interrupted. Young birds that pass the migration route for the first time, when choosing places to stop, can react to the behavior of adult birds that have settled for rest. Among waterfowl, storks, and cranes, which often fly in family groups, adult birds can simply lead the young to traditional stopping places. There is no other way to explain how these places, sometimes located far away from the main migration route, are preserved for decades and even centuries as permanent stops (see Chapter 3). Once in these places, young birds probably determine their coordinates and, during subsequent migrations, find them without much difficulty. Birds often make a loop-like flight when the autumn migration route does not coincide with the spring one. In this case, birds may have several fixed stops along the autumn and spring migration route (Fig. 36). Thus, I assume that migratory birds can navigate not only in relation to the main targets located in the breeding and wintering areas, but also in relation to additional targets located along the migration route, in the moulting area, etc.