The book is devoted to one of the most interesting and mysterious problems of ornithology - the problem of fidelity of migratory birds to their homeland and home. The feeling of "loyalty to the house" is inherent in a variety of animals - from insects to primates, including humans. This feeling has an instinctive basis and manifests itself in an individual in an effort to return home - to a place familiar to her after a temporary absence. For migratory birds, "home" can mean the place of birth, nesting, wintering.
For readers interested in problems of biology and ornithology, as well as for nature lovers.
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During migration, birds cover great distances to get to the wintering or nesting area, often located on another mainland. It is hard to imagine how birds manage in the most difficult conditions, when they are constantly blown off course by the wind, at night, often in full cloud cover, when neither stars nor earth are visible, to find the right path, it is difficult to imagine. But they find it even when they are young and inexperienced. At first, they thought that the young ones fly with adult birds, which show them the way. As an example of "family" flights, flocks of swans, geese or storks, consisting of parents and children, are usually cited, which often stay together not only during the autumn migration, but also during the winter until the nesting season. Special experiments were required to detain young birds in the nesting area in order to prove that the young are able to independently find the right way to wintering. Such experiments were carried out by E. Schutz with white storks. He caught young storks from the eastern population, from which birds usually fly to Africa for the winter in a southeasterly direction, skirting the Mediterranean Sea from the east, and released them, after the adults had flown away, in the western part of Germany, from where storks fly southwest way. As the finds of ringed storks showed, in the same year, the young flew along their southeastern route, which is innate for them.
Rice. 33. Results of the experiment on the importation of young and adult common starlings from the autumn migration route from Holland to Switzerland.
Light circles - places of finds of adult birds after release, dark circles - places of finds of young birds.
Thin arrows indicate the direction of bird introduction; light and dark arrows - the direction of movement of adult and young birds after release.
Later, A. Perdek transported about 15 thousand starlings during the autumn migration from Holland to Switzerland and Spain in the late 50s. In the first experiment, he released 11 thousand starlings in three places in Switzerland (750 km southeast of the place of capture). In the same year, 354 returns were received, 131 of them from distances over 50 km. from the place of release. These finds of displaced starlings showed that young birds, which migrated 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 wintered in an area unusual for them (in Southern France and Spain). Returns in subsequent years showed that the birds returned to these areas in the future. Adult birds showed a double distribution after release: one group continued to fly like juveniles, but the other returned from their characteristic wintering areas (England and northern France). The third group (19 individuals) gave returns from the northern regions, from the traditional starling migration route. In the next experiment, 3600 starlings caught in autumn in Holland were transported to Barcelona (Spain). Again, young birds continued to migrate in a compass southwesterly direction, while adults shifted towards wintering.
Based on these data, Perdek concluded that young birds in their first migration follow an 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-olds would behave after the displacement of the first year in the spring, since they should already know, like adults, where their nesting area is.
Perdek conducted such an experiment. About 3 thousand young starlings caught in Holland were released in Switzerland in February and March. In the same year, part of the birds were found in their nesting area, as expected. However, some birds remained nesting in the release area, some of these birds returned here for nesting in subsequent years. This suggests that in some cases, the primary information about the nesting area obtained by the bird at juvenile age 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 suggestions have been put forward: 1) that birds have an innate knowledge of the location of wintering grounds, 2) that they fly in the direction of wintering grounds until they use up all the energy “destined” for migration, 3) that they are guided by a change in the ratio of the length of day and night (photoperiod) and biological clock for the timely completion of migration, and even 4) that they use the temperature gradient, i.e., they fly in the direction of increasing temperatures in autumn. None of these assumptions has been confirmed experimentally. 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 directionality, 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 it is possible to get, for example, from Siberia to a small area in Africa, but nevertheless this is so far the only way that has experimental confirmation. In numerous experiments to test the duration of migratory disturbance in cellular conditions in captive-bred birds of different species and populations, evidence was obtained that the level and duration of migratory activity are innate and specific for a species, population, and even for different individuals from the same population.
Recently, G. Bibach showed in experiments on the hybridization of migratory and sedentary individuals in the robin that more individuals with migratory activity (89%) were born in the group of descendants from migrant parents (89%) than in the group of descendants from sedentary parents (53%). Similar data were obtained for the black-headed warbler. Thus, it was found 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 lentils in laboratory conditions, I found that in young individuals, a decrease in fat reserves and migratory activity occurs at strictly defined times, when migration is buried in these species in nature, while in For adults, the end of the migratory state in captivity is delayed by about 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. For the final cessation of migration, an adult bird needs to receive information that it has reached its wintering place. Under cellular conditions, it naturally cannot obtain this information. In the spring, the end of the migratory state in the chaffinch is delayed both in adults and first years, if they are detained on the migration route, but ends in time, as shown by M.E. Shumakov and N.V. Vinogradova, if the birds are kept in their nesting area.
Rice. 34. Terms of the end of the migratory state in young (1) and adult (2) common lentils (A) and finches (B) detained during the autumn migration on the Curonian Spit.
Later, E. Ketterson and V. Nolan, recording in autumn the intensity of nocturnal 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 wintered here less often in the past years, fat deposition and nocturnal activity were significantly lower than in the other two groups, which included birds brought to the study area from Canada, from nesting sites. In spring experiments, there were no noticeable discrepancies in these indicators for all three groups. The authors concluded that the presence of birds on familiar wintering grounds before the start of autumn migration can suppress the development of the migratory state.
In another experiment, the researchers analyzed factors that determine the end of spring migration in previously breeding indigo buntings. For this purpose, they caught 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 aviation, where the photoperiod corresponding to the areas of migration and wintering of this species was automatically maintained. Before the start of spring migration, 22 males caught in individual territories were divided into two equal groups. One group (experimental) of birds was released directly on their last year nesting sites, the other (control) was transported and released the next day at 1000 km. south of the study area. The remaining 24 males were placed in cages (where the motor activity of birds 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 while nesting. After all these operations, a series of control captures of males that started nesting in the study area was made. From the experimental group, 4 males were caught, moreover, on their last year's nesting sites. From the control group, brought to 1000 km., 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 curious experiment came to the conclusion that indigo buntings, in order to stop spring migration, need to go directly to the nesting territory they had previously captured. If the 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, then 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, similarly to how they do it when imprinting the future nesting area (see Chapter 5). However, it is clear both from our and these experiments that the time of the end of spring and autumn migration in adult birds is primarily determined by whether they have reached the nesting (wintering) area familiar to them or not.
Recently, facts have appeared that indicate that not only the total duration of migration is genetically programmed, but also its strategy on different sections of the route. Gwinner and Berthold found that in long-distance migrants (warblers and warblers) the most intense nocturnal activity in autumn in cellular conditions occurs at a time when their free relatives cross the Mediterranean and the Sahara at maximum speed. Then the migratory restlessness of the caged birds gradually decreases, just when the free birds also slow down their migratory 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. W. Neuzzer tested the direction of migratory activity in Emlen's round cages in captive-bred blackheads from two populations - from Germany, migrating to the southwest in autumn, and from Austria, flying to the southeast. Significant differences were obtained in the orientation of these groups of birds (241° in birds from the FRG and 185° in 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 ringed bird finds have shown, 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 bred 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 that it is time for them to change their direction of flight? It turned out that even such information is in the genetic program. Checking in round cages the migratory orientation throughout the autumn in young garden warblers bred in captivity, Gwinner found that in August-September the birds choose the south-western direction, and in October-December - the south-east (Fig. 35). Further experiments with reared warblers showed that a change in the direction of jumping in birds in a round cage was observed even when the birds could not see the sky. Gwinner and Viltchko suggested that the change in orientation occurs along 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 guided not by the poles of the Earth's magnetic field, but by the direction of declination: the north for the bird is where the angle between the magnetic inclination and the gravity vector is smaller. A magnetic compass of this kind is only useful within one hemisphere. At the equator it will not act, but beyond the equator it will give the opposite direction. According to the magnetic compass, V. Viltchko believes, the astronomical compass is tuned. The star compass, the existence of which was proved by S. Emlen, and the rotation of the firmament are used, according to Viltchko, only by night migrants during flights. The solar compass, which includes determining the direction by sunset, is also an additional orientation system that is adjusted in the first months of a bird's life according to the primary, i.e. magnetic, system. Viltchko believes that the role of the solar compass in migratory orientation is currently overestimated.
Other researchers disagree with this view. In particular, K. Able believes that the solar compass develops in migratory birds, regardless of the magnetic one. The star compass is also formed independently by sighting the axis of rotation of the star sphere. The polar point gives the reference direction relative to which the inherent migration azimuth is realized. F. Moore, E. B. Katz and other researchers prove that the determination of the direction by migratory birds occurs mainly by the sun during sunset. The stars are used only to maintain this direction. Which of these points of view is more correct, further research will show.
The direction of flight of birds during migration can be influenced by other factors: wind, landmarks, magnetic anomalies, etc. Can birds correct their path after exposure to such factors? P. Evans analyzed the autumn course of night migrants of Scandinavian origin, who leave Norway in a south-south-westerly direction, passing through southern England and western France. If, while crossing the North Sea, the birds are caught in strong easterly winds, they can be blown away and they will pass along the northeast coast of Britain. Do the birds continue to migrate in the standard direction, or will they reorient themselves to the south or southeast to enter the normal migratory path? Evans checked for orientation in round cages the off-course birds he had caught in north Yorkshire. In these experiments, many birds showed a southerly and southeasterly orientation, i.e., they tried to compensate for the shift. Evans later compared autumn and winter finds of common redstarts and pied flycatchers ringed north of Yorkshire with those taken from the coast south of Yorkshire. Returns from displaced birds showed the same geographic distribution as in non-displaced birds. Evans concluded that the two species had the ability to correct bias.
Radar observations show that flying birds compensate for about? - ? influence of wind on migratory flight by changing the speed. G. Klein's calculations showed that for a distant migrant - a garden warbler, the maximum displacement reaches 900 km, which is only 1/10 of the migration distance for extremely distant migrants, while for a black-headed warbler (near migrant) such an error is about a third of the distance, provided that the birds half compensate for the influence of the wind. Probably for this reason, Klein suggests, nearby 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 spread of directions than adult birds. In particular, F. Moore discovered this in the savannah bunting when comparing orientational behavior in Emlen cells in young and adult birds in North Dakota. He suggested that differences in orientation between adults and juveniles reflect the importance of migratory experience. Young people may make more orientational mistakes, they do not have information about the ultimate goal of migration. Moreover, adult birds may know some sections 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 replenishment of fat reserves. There may be several such places on the track. Therefore, it is quite possible that adult birds with migratory experience use a different strategy than is usually assumed to migrate from nesting areas to wintering areas and vice versa.
Rice. 36. Hypothetical scheme of "staged" migration of migratory birds during the first and subsequent flights between nesting and wintering areas.
1 - nesting area (purpose of spring migration), 2 - wintering area (purpose of autumn migration), 3 - main stopping places of birds during migration (intermediate goals 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 dashed line is the path of the subsequent migration of an adult bird.
I think that birds, primarily waterfowl, can implement a “staged” migration strategy, which consists in the fact that birds fly from one place they know on the track to another and so on to the final goal (Fig. 36). If for any reason they go off course (for example, they are blown away by the wind), then they tend to get to the nearest point on the track they are familiar with. There are facts that displaced birds (see the description of A. Perdek's experiments) tend to enter 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, may react to the behavior of adult birds that have settled for rest. In waterfowl, storks, 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 looping flight when the autumn migration path does not coincide with the spring one. In this case, the birds may have several fixed stops along the autumn and spring migration routes (Fig. 36). Thus, I assume that migratory birds can navigate not only in relation to the main targets located in the nesting and wintering areas, but also in relation to additional targets located on the migration route, in the molting area, etc.
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Have you ever thought about how birds find the right path, overcoming boundless oceans and vast deserts during their flights and migrations (more about)? What landmarks do they use, what sense organs are they guided by? Hunters often ask these questions, and our today's publication is ready to answer this question ...
For a bird to be well oriented in space means, first of all, to have reliable information about their environment. After all, its changes in some cases can be fatal for the bird, in others - on the contrary, favorable, but it needs to know about both in a timely manner. The animal's behavior will depend on how its sense organs perceive these changes and how their higher organ of orientation, the brain, evaluates them. It is clear that success in the struggle for existence will accompany the individual whose sense organs and brain will quickly assess the situation and whose response will not be long in coming. That is why, speaking about the orientation of animals in space, we must keep in mind all 3 of its components - landmark stimulus, perceiving apparatus, and response.
Despite the fact that in the process of evolution all these components were formed into a certain balanced system, not all landmarks are perceived by birds, since the throughput of their sense organs is very limited.
So, birds perceive sounds with a frequency of up to 29,000 Hz, while bats - up to 150,000 Hz, and insects - even higher - up to 250,000 Hz. Although, from a physical point of view, the auditory apparatus of a bird in the air is very perfect, it fails in water, and the sound wave travels to the auditory cell in an uncomfortable way - through the whole body, while the eardrum and auditory canal are completely blocked. And, how underwater hearing would help fish-eating birds! It is known that dolphins with the help of hearing can accurately determine the type of fish, its size, its location. Hearing for them completely replaces vision, especially since the possibilities of the latter are even more limited - the viewing space, for example, for kestrel and barn owl, is 160 degrees, for pigeons and passerines - about 300 degrees, for woodpeckers - up to 200 degrees. And, the angle of binocular vision, that is, vision with two eyes, which allows you to especially accurately examine an object, is 30-40 degrees in most birds, and only in owls, with their characteristic face, up to 60 degrees.
The sense of smell in birds is even less possible - the direction of the wind, dense thickets and other obstacles make it very difficult to navigate by smells. Even urubu vultures, descending to carrion from a great height, are guided by a thin trickle of the smell that has risen upward, and they are far from always able to use this type of orientation.
The absence of the necessary sense organs leads to the fact that many of the natural phenomena, as landmarks, are not used by birds or are not used enough. Experimental data and individual field observations give a very contradictory picture. In certain situations, for example, powerful radio stations affect the orientation of birds, however, this does not always happen and not in all cases. Birds certainly perceive changes in pressure, but how subtly the pressure gradient can be used as a guide is completely unclear. Thus, the orientation abilities of each individual individual are very limited. Meanwhile, for birds with their open way of life, surrounded by a mass of enemies and other worldly troubles, reliable orientation is a matter of life and death. And, often, their insufficient individual capabilities are corrected through communication with other individuals, in a flock, in a nesting colony.
Every hunter knows that a single bird is much easier to approach than a flock that has many ears and eyes, and where the warning cry or flight of one individual can alarm the rest. Various calls, postures, bright spots in coloring provide the birds with joint behavior in the flock and communication between them. A kind of group, secondary orientation is being created, where the possibilities of orientation, the individual experience of one bird are significantly increased at the expense of other birds. Here it is no longer necessary to see the predator itself, it is enough to hear the warning cry of a neighbor. Of course, the neighbor screams not at all because he wants to warn other birds - he has this natural reaction to the enemy, however, the rest of the birds perceive this cry precisely as a signal of danger.
The matter becomes even more complicated and the possibilities of one individual increase even more when communication is established between birds of different species within the community. For example, the cry of a small bird at an owl gathers a very diverse society in the forest - tits, warblers, nuthatches, finches, crows, jays and even small predators. Exactly the same understanding is established between waders, gulls and crows on the sea shallows, between various thrushes, etc. In the forest, the role of a signalman is played by a magpie - the cry of which, for example, when a large predator or a person approaches, is perceived not only by a wide variety of birds, but also by mammals. Here group orientation goes even further.
In terms of visual acuity, birds have no equal. The amazing abilities of various predators in this regard are well known. The peregrine falcon sees small birds at a distance of over a kilometer. In most small passerines, visual acuity is several times greater than human visual acuity. Even pigeons distinguish 2 lines at an angle of 29 degrees, while for a person this angle should be at least 50 degrees.
In addition, birds have color vision. You can, for example, teach chickens to peck at red grains and not peck at blue or white ones, to run towards the blue one in the direction of the red screen, etc. This is indirectly proved by the amazing variety of bird coloration, represented not only by all the colors of the spectrum, but also by their most diverse combinations. Coloring plays a big role in the joint behavior of birds and is used by them as a signal when communicating. Finally, it can be added that recent experiments by Polish researchers confirmed the ability of birds to perceive the infrared part of the spectrum, and therefore to see in the dark. If this is true, then the mysterious ability of birds to live in darkness or in twilight becomes clear. In addition to owls, other birds are apparently capable of this - in the conditions of a long Polar night in the Arctic, white and tundra partridges, raven, gyrfalcon, tap-dancing, snow bunting, and various guillemots remain to winter.
These features of bird vision are provided by the remarkable anatomical structure of their eyes. First of all, birds have relatively huge eyeballs, which in owls and falcons, for example, are about 1/30 of their body weight, in woodpeckers - 1/66, in magpies - 1/72. The bird's eye has a large number of cone sensory cells necessary for sharp vision, equipped with red, orange, green, or blue oil globules. Experts believe that oil balls enable the bird to distinguish colors.
Another feature of the bird's eye is its fast and accurate adjustment - accommodation. This is done by changing the curvature of the lens and cornea. Rapid accommodation allows, for example, a falcon hitting a flock of ducks from a great height to clearly see the birds and correctly estimate the distance at any moment of its throw. Steppe birds also have a special plane of sensitive cells in the retina of the eye, which makes it possible to view the horizon and distant objects especially clearly and at a great distance. The eyes of cormorants, auks, ducks (o), loons hunting for fish under water have special devices that provide underwater vision to birds.
Good vision of birds of prey is used in.
The sense of smell of birds is still little explored and very mysterious. For a long time it was believed that birds have a poor sense of smell, but new experiments suggest otherwise. Songbirds, ducks, some chickens distinguish smells well, for example, clove and rose oil, benzaldehyde ...
Ducks are able to find a box of food by a special smell from a distance of 1.5 meters and go straight to it. Urubu vultures, some nightjars, petrels, and gulls have a good sense of smell. Albatrosses gather on lard thrown into the water from a distance within a radius of 10 kilometers. Hunters also know cases when crows found pieces of meat buried in the snow. Nutcrackers and kukshas quite accurately look for pieces of food hidden in the litter in the aviary, being guided solely by their sense of smell.
Birds, in general, have a mediocre taste, and only in certain groups, such as granivorous birds, predators and noble ducks, does it reach some development.
A large number of nerve endings in the form of tactile bodies are located in the skin of birds, at the base of feathers, and in the bones of the limbs. With their help, the bird can determine, for example, the pressure of the air stream, the strength of the wind and the temperature of the air. These nerve endings are very diverse in structure and function, and there is an opinion that it is among them that one should look for the so far unknown organs of perception of electric and magnetic fields.
A large number of tactile bodies are located at the tip of the beak of the snipe, woodcock and other shorebirds, which obtain food by probing wet earth, mud and mud. In lamellar beaks, such as mallards, the tip of the beak is also covered with sensitive bodies, which is why the maxillary bone, like that of the woodcock, looks completely cellular.
Perceiving a single environment in its essence in the form of separate stimuli, landmarks, the organs of spatial orientation of the bird isolate only some of the qualities of the object. At the same time, the space in which these landmarks are located is also not unlimitedly analyzed by them. Individual landmarks are perceived at long distances and have a maximum range, such as sound. Others act in close proximity, on contact, like the tactile bodies of the beak. The action of the smell of carrion for vultures soaring in the air is limited to a narrow stream of rising air. All sense organs, therefore, have their own spatially limited spheres of action, within which the analysis of objects and landmarks is carried out.
The spheres of action of the sense organs have their own biologically justified orientation. When it comes to especially critical situations in the life of a species, such as catching prey or evading danger, one sense organ, for example, sight, hearing or smell, is not enough, therefore, several sense organs act together. There is a layering of their spheres of action, and the object that is within their limits is analyzed and will be perceived more comprehensively and accurately.
Thus, owls and harriers, whose existence depends on how accurately they determine the location of the mouse, and the action often takes place in dense thickets or with limited visibility of the field of vision and hearing, have a common forward orientation, resulting from the forward displacement of the eyes and ears - such a face is a very characteristic feature of owls and harriers.
This duplication of the sense organs with each other and provides an integral perception of the environment, natural landmarks. Of course, this wholeness is ensured not only by the sense organs, but also mainly by the brain, which combines information coming through individual channels and evaluates the situation as a whole. First of all, higher forms of orientation, the so-called homing, return to the nesting place of artificially distant birds, orientation during seasonal flights, weather forecasting, counting, etc. are associated with the work of the brain.
An open mobile lifestyle, a constant alternation of various landmarks, the need for communication developed in birds the rudiments of rational activity and the ability for elementary abstractions. If you sneak up on the crows feeding in the field and at the same time go down into the ravine to disguise yourself, then the birds will be waiting for you at the other end of the ravine, where you will have to find yourself, maintaining the original direction of movement. A flock of geese or cranes watching a fox creeping up on them will do the same.
However, an assessment aimed at the movement of a landmark, partly its extrapolation, is no less important in complex forms of orientation than the ability to quantify orientation. In experiments, it was possible to teach chickens to peck any grain of their choice - the second, third, etc., but pigeons were able to be taught to distinguish between different combinations of grains. Magpies and crows are also good at distinguishing between different sets of objects, and even the number of people and animals. Birds, for example, can distinguish 5 objects from 6 without counting - a task that is not always accessible even to humans. Special experiments have also shown that birds are good at distinguishing the contours and shapes of objects, geometric shapes, etc.
These abilities play a particularly important role in the celestial navigation of birds - the use of celestial bodies as landmarks.
Thus, warblers were placed in a planetarium and the direction of their flight was monitored at different positions of the starry sky. It was possible to prove that the general picture of the starry sky can be used by them as a guide during seasonal flights. It is easy to imagine the difficulties that arise in this case for the bird - the need to extrapolate the movement of the stars, to accurately, up to 15-20 minutes, to feel the time, to perceive various combinations of constellations, the number of stars, etc.
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. Nearly the same migration route is observed for the brown-winged plover Charadrius dominica, nesting in the Siberian tundra, 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. Observations from aircraft and radar found 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 (change 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 still no answer to this question. 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 migrating 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.
For a bird to be well oriented in space is, first of all, to have reliable information about the environment. After all, its changes in some cases can be fatal for the bird, in others, on the contrary, favorable, but it needs to know about both in a timely manner. The animal's behavior will depend on how its sense organs perceive these changes and how their higher "organ" of orientation, the brain, evaluates them.
It is clear that success in the struggle for existence will accompany the individual whose sense organs and brain will quickly assess the situation and whose response will not be long in coming. That is why, speaking about the orientation of animals in space, we must keep in mind all three of its components (orientation stimulus, perceiving apparatus, response).
Despite the fact that in the process of evolution all these components are formed into a certain balanced system, not all landmarks are perceived, since the “throughput” of the sense organs is very limited.
Thus, birds perceive sounds with a frequency of up to 29,000 Hz, while bats up to 150,000 Hz, and insects even higher - up to 250,000 Hz. Although from a physical point of view, the auditory apparatus of a bird in the air is very perfect, it fails in water, and the sound wave travels to the auditory cell in a long and "uncomfortable" way - through the whole body, while the eardrum and auditory canal are completely blocked. And how underwater hearing would help fish-eating birds!
It is known that dolphins with the help of hearing can accurately determine the type of fish, its size, its location. Hearing for them completely replaces sight, especially since the possibilities of the latter are even more limited: the viewing space, for example, for kestrel and barn owl is 160 °, for pigeons and passerines - about 300 °, for woodpeckers -. up to 200° etc.
And the angle of binocular vision, that is, vision with two eyes, which makes it possible to examine an object with particular accuracy, is 30-40 ° in most birds, and only up to 60 ° in owls with their characteristic “face”. Birds have even fewer opportunities for smelling - the direction of the wind, dense thickets, etc. interference makes it very difficult to navigate by smells. Even urubu vultures, descending to carrion from a great height, guided by a thin stream of smell that has risen to the top, and they are far from always able to use this type of orientation.
The absence of the necessary sense organs leads to the fact that many of the natural phenomena, as landmarks, are not used by birds or are not used enough. Experimental data and individual field observations give a very contradictory picture. In certain situations, for example, powerful radio stations influence the orientation of birds, but not always, not in all cases. Birds certainly perceive changes in pressure, but how subtle and whether pressure gradient 2 can be used as a guide is completely unclear.
Thus, the orientation abilities of each individual individual are very limited. Meanwhile, for birds with their open way of life, surrounded by a mass of enemies and other “worldly” troubles, reliable orientation is a matter of life and death. And insufficient individual capabilities are corrected through communication with other individuals, in a flock, in a nesting colony. Every hunter knows that it is much easier to get close to a single bird than to a flock that has many ears and eyes, and the warning cry or flight of one individual will alarm everyone else.
Various calls, postures, bright spots in coloring ensure the joint behavior of birds in a flock, the connection between them. A kind of group, secondary orientation is being created, where the possibilities of orientation, the individual experience of one bird are significantly increased at the expense of others. Here it is no longer necessary to see the predator itself, it is enough to hear the warning cry of a neighbor. Of course, the neighbor screams not at all because he “wants” to warn others: he has this natural reaction to the enemy, but the rest of the birds perceive this cry precisely as a signal of danger.
The matter becomes even more complicated and the possibilities of one individual increase even more when communication is established between birds of different species within the community. For example, the cry of a small bird “at an owl” gathers a very diverse society in the forest: tits, warblers, nuthatches, finches, crows, jays, even small predators. Exactly the same “understanding” is established between waders, gulls and crows on sea shallows, between various thrushes, etc. In the forest, the role of a signaler is played by a magpie, whose cry, for example, when a large predator or a person approaches, is perceived not only by a variety of birds, but and mammals. Here the group orientation goes even further.
Vision, hearing and smell are the main "bricks" that make up the general building of spatial orientation. In terms of visual acuity, birds have no equal. The amazing abilities of various predators in this regard are well known. The peregrine falcon sees small birds at a distance of over a kilometer. In most small passerines, visual acuity is several times greater than human visual acuity. Even pigeons can distinguish between two lines that run at an angle of 29°, while for humans this angle should not be less than 50°.
Birds have color vision. You can, for example, teach chickens to peck at red grains and not peck at blue ones, or to run in the direction of a red screen and not run up to a blue one, etc. This is indirectly proved by the amazing variety of bird coloration, represented not only by all the colors of the spectrum, but also by their most diverse combinations. Coloration plays a large role in the cooperative behavior of birds and is used as a signal in communication.
Finally, it can be added that recent experiments by Polish researchers seem to have confirmed the ability of birds to perceive the infrared part of the spectrum and, consequently, to see in the dark. If this is so, then the still mysterious ability of birds to live in darkness or in twilight lighting will become clear. In addition to owls, other birds are apparently capable of this: in the conditions of a long polar night in the Arctic, white and tundra partridges, raven, gyrfalcon, tap-dancing, snow bunting, and various guillemots remain to winter.
These features of bird vision are provided by the remarkable anatomical structure of their eyes. First of all, birds have relatively huge eyeballs, which in owls and falcons, for example, are about Vso of body weight, in woodpeckers g/bb" in magpies 1/?2. The bird's eye has a large number of sensory cells - cones, necessary for sharp vision, equipped with red, orange, green or blue oil globules.
It is believed that oil balls enable the bird to distinguish colors. Another feature of the bird's eye is its quick and precise adjustment - accommodation. This is done by changing the curvature of the lens and cornea. Rapid accommodation allows, for example, a falcon hitting a flock of ducks from a great height to clearly see the bird and correctly estimate the distance at any moment of its throw. Steppe birds have a special strip of sensory cells in the retina of the eye, which makes it possible to view the horizon and distant objects especially clearly and at a great distance. The eyes of cormorants, auks, ducks, loons hunting for fish under water have special devices that provide underwater vision.
The sense of smell of birds is still little explored and very mysterious. For a long time it was believed that birds have a poor sense of smell. however, new experiments say otherwise. Songbirds, ducks, some chickens distinguish smells, for example, clove and rose oil, amyl acetate, benzaldehyde. The duck found a box of food by a special smell and from a distance of 1.5 meters went straight to it. Urubu vultures, some nightjars, petrels, and gulls have a good sense of smell.
Albatrosses gather on lard thrown into the water from a distance within a radius of tens of kilometers. Hunters know cases when crows found pieces of meat buried in the snow. Nutcrackers and kukshas quite accurately search for odorous pieces of food hidden in the litter in the enclosure, apparently also being guided solely by the sense of smell.
Birds, in general, have a moderately developed taste, and only in certain groups, as, for example, in granivorous birds, predators and noble ducks, does it reach some development.
A large number of nerve endings in the form of tactile bodies are located in the skin of birds, in the bases of feathers, and in the bones of the limbs. With their help, a bird can determine, for example, the pressure of air jets, wind strength, temperature, etc. These nerve endings are very diverse in structure and functions, and there is an opinion that it is among them that one should look for the yet unknown organs of perception of electric and magnetic fields etc.
A large number of tactile bodies are located at the tip of the beak of the snipe, woodcock and other shorebirds, which obtain food by probing the wet earth, mud and mud. In lamellar-billed birds, such as mallards, the tip of the beak is also covered with sensitive bodies, which is why the maxillary bone, like that of the woodcock, looks completely cellular.
Perceiving a single environment in its essence in the form of separate stimuli, landmarks, the organs of spatial orientation isolate only some of the qualities of objects. At the same time, the space in which these landmarks are located is also not analyzed indefinitely. Some landmarks are perceived at great distances and have a maximum "range", such as sound, others act in close proximity, upon contact, such as the tactile bodies of the beak.
The action of the smell of carrion for vultures soaring in the air is limited to a narrow stream of rising air. All sense organs, therefore, have their own spatially limited spheres of action, within which the analysis of objects and landmarks is carried out.
The spheres of action of the sense organs have their own biologically justified orientation. When it comes to especially critical situations in the life of a species, such as catching prey or avoiding danger, one sense organ, say, sight, hearing or smell, is not enough, so several sense organs act together. Spheres overlap.
Steppe birds have a special strip of sensory cells in the retina of the eye, which makes it possible to see especially clearly at great distances.
So, in owls and harriers, whose existence depends on how accurately they determine the location of the mouse, and the action often takes place in dense thickets or with limited visibility, the fields of vision and hearing have a common, forward orientation. The “face” formed as a result of the anterior contraction of the eyes and ears is a very characteristic feature for both owls and harriers.
This duplication of the sense organs with each other and provides an integral perception of the environment, natural landmarks. Of course, this wholeness is ensured not only by the sense organs, but mainly by the brain, which combines information coming through separate "channels" and evaluates the situation as a whole.
The highest forms of orientation, the so-called “homing” (return to the nesting place of artificially distant birds), orientation during seasonal flights, weather forecasting, counting, etc., are primarily associated with the work of the brain.
An open mobile lifestyle, a constant alternation of various landmarks, the need for communication developed in birds “the rudiments of rational activity and the ability for elementary abstractions.
If you sneak up on the crows feeding on the field and at the same time descended into a ravine to disguise, then the birds will be waiting for you at the other end of the ravine, where you should find yourself, maintaining the original direction of movement. A flock of geese or cranes watching a fox creeping up on them will do the same.
However, the assessment of the direction of movement of a landmark, partly its extrapolation, is no less important in complex forms of orientation than the ability to quantify landmarks.
In experiments, it was possible to teach chickens to peck any grain of their choice - the second, third, etc., pigeons - to distinguish various combinations of grains. Magpies and crows distinguish well between different sets of objects, for example, the number of people, animals. Birds, for example, without counting, can distinguish 5 objects from 6 - a task that is not always accessible even to humans. Special experiments also showed that birds distinguish well the contours and shapes of objects, geometric figures, etc.
These abilities play a particularly important role in the celestial navigation of birds - the use of celestial bodies as reference points.
Warblers were placed in a planetarium and the direction of their flight was monitored at different positions of the starry sky. So it was possible to prove that the general picture of the starry sky can be used as a guide for seasonal flights. It is not difficult to imagine the difficulties that a bird faces with an atom: the need to extrapolate the movement of the stars, exactly, up to 15-20 minutes. Seagulls have a good sense of smell; broody.
From this point of view, the orientation in the daytime, according to the sun, is somewhat simpler. But here, before the bird, it becomes necessary to estimate the angular displacement of the sun and have a very accurate "internal clock". This is still easier than using the star as a reference point, which may be why this view has more adherents and is less controversial. There are attempts to explain the nocturnal flights of birds with the help of solar orientation: at night, birds fly in the direction that they have chosen during the day in the light of the sun.
In addition to these general "universal" landmarks, other, local ones may be of great importance. Where constant winds blow, birds can use the direction of the wind. The direction of mountain ranges, river beds, sea coasts - even wave crests can also play the role of such landmarks.
Despite the two-century history of the study of bird migration, the issue is far from clear even today. Failed. Attempts to explain flight orientation solely by one reference point: Coriolis forces. arising from the rotation of the earth, magnetic or electric fields, etc. Experimental verification of them showed conflicting results, apparently due to the fact that a complex of landmarks, and not one landmark, is used during flights. In essence, the search for an “organ of orientation” also turned out to be useless.
In the final assessment of the situation, the brain is of decisive importance, and the key to the "mechanism" of orientation during flights lies in the study of the brain activity of birds.
A completely special, no less interesting, category of phenomena is "homing" - the return to the "home" of artificially removed birds. Forty years ago, experiments with terns showed that, 1,200 kilometers away from nesting sites, they return after a few days. Swallows, starlings, shrike, wrynecks and other birds have also discovered this ability. The petrel returned from Venice, where it was introduced, to its nest in Scotland in 14 days, covering 6,000 kilometers. The white-bellied swift returned from Lisbon to Switzerland within three days.
The mechanisms of homing are also currently unclear. So far, we can say that, apparently, local landmarks are used to a greater extent, and, probably, a whole complex of them. Extrapolation and the ability to quantify phenomena, the internal clock, and such an important property of brain activity as memory are of particular importance.
“The spatial orientation of birds is an extremely interesting question at all levels of orientation, from the simplest to the most complex. It acquires great importance now in connection with bionics and the problem of controlling the behavior of animals.
Bionics is interested in the means and ways of visual, auditory and other types of orientation, the work of auxiliary structures that de-energize the best signal reception and processing, and the evaluation of the final information in the brain centers. Birds are especially attractive to bionics because of their small size, high reliability and performance, wide range of action, efficiency and other qualities of their sense organs, which are much superior to everything that modern technology has.
By creating artificial landmarks, a person evokes the necessary motor reactions in animals under natural conditions. In some cases, in this way it is possible to attract many animals to a limited area, in others, on the contrary, to scatter, scare them away from those places where they are undesirable.
An energetic search is currently underway for such means of controlling the behavior of animals and, in particular, birds. Acoustic, optical and olfactory landmarks have already been found, some of which are used in practice. Hunting and fisheries, the fight against harmful insects, the protection of humans from bloodsuckers - this is not a complete list of industries where they can be used. Finally, this opens up the possibility of a reasonable, rational regulation of the number of natural populations.
winged wanderers
The most difficult, still fraught with many mysteries, question in the study of bird migrations is the question of their orientation. For many years, scientists struggled to resolve it, either looking for special "organs of orientation", or attributing the phenomenal abilities of migratory birds to instincts, "an innate sense of direction." How do birds find directions to nesting and wintering grounds? The training of young birds by old ones plays an insignificant role here, since young birds often fly away earlier than adults and travel separately. Birds also cannot remember the way according to visible signs, since many fly at night, behind the clouds, and return to nesting places by another way. Many ornithologists have experimented with birds, bringing them in closed boxes hundreds of kilometers from home. The boxes were sometimes rotated along the road to eliminate any memorization. Starlings were taken 100-300 km from the nest, nightingales - 270 km, urban swallows - 317 km. All of them quickly returned home. Common petrels from Venice returned to the coast of Wales after flying 6,000 km in 14 days. The albatrosses returned to Midway Island after flying 6,590 km in 32 days. Common terns returned, overcoming a distance of 600 km, herring gulls - 1300-1400 km.
There are many hypotheses about the mechanisms of orientation of birds during flights. Some of them have long been discarded as not confirmed by facts, others look more convincing. However, the issue of bird navigation still cannot be considered resolved. Let's consider several hypotheses.
Orientation by landscape features seems to be the most natural from the point of view of a person. There are so-called guide lines: river valleys, sea coasts, ravines in the mountains and other large landscape details that a bird can see from the air. But in order to navigate along these lines, the bird must see them at least once. Thus, the orientation of young birds flying on their own is excluded by this sign. Birds flying at night cannot use guide lines either. Many seabirds are perfectly oriented over the open sea, where there are no signs. In this case, the hypothesis is also not confirmed.
Infra-red thermal radiation from the south cannot signal the choice of path to birds, since birds do not have increased sensitivity to the infrared part of the spectrum.
Italian scientists have put forward a hypothesis that certain areas of the Earth's surface have a specific smell. Ornithologists from Germany have suggested that olfactory sensations can help birds find their native places. They set up an experiment to study the feeling of home (homing) in pigeons. The birds, divided into two groups, control and experimental, were taken 180 km from the dovecote. The olfactory nerves were preliminarily cut in the experimental group. The operated pigeons strongly deviated from the course, unlike the birds of the control group. But an experiment carried out according to the same scheme with a swift did not confirm this hypothesis. Most ornithologists do not accept it, since in birds the sense of smell is generally less developed than in other vertebrates.
The hypothesis of having an innate sense of direction has not been proven.
