What is seasonal animal migration? Aerospace methods for studying animal migrations Why animals migrate

13.06.2019

Graduation work

Performed by Viktor Tkachenko

Secondary school - Lyceum No. 265

St. Petersburg

I. Introduction

The entire animal world of the planet is in constant motion: from the smallest planktonic organism to giant whales in the seas and oceans, from tiny midges to huge albatrosses in the air, from such small mammals like lemmings, to elephants - everything moves, everything moves in the surrounding space, looking for the best habitats, rich in food or convenient for breeding. Some animals make their movements irregularly, others strictly cyclically: once a day, a month, a season, a year, or even once every few years. For some inhabitants of the planet, such a journey is the only one in life, while others undertake it many times. It is as if a gigantic pump, or rather a multitude of pumps, pumps the animal population of the planet, mixing it and directing it along one or another channel.

However, all this looks chaotic only at first glance. Animal movements are governed by complex laws closely related to changes in the environment. In fact, the movements themselves are the most important adaptations that expand the ecological capabilities of the species.

Animal movements are strictly limited in space and time. They follow certain rhythms. It would seem a contradiction: on the one hand, constant movement, on the other, binding to certain points in space, certain routes, territories that ensure the existence of each separate species, a separate population, a separate organism in infinitely diverse conditions environment. Therefore, the movements of animals are so diverse and complex, so difficult to compare and classify. The classification of migrations is difficult not only because of their insufficient knowledge, but also because of the diversity of their manifestations in different groups of animals.

Every animal can face problems of food shortage, overpopulation, excess predators or habitat destruction, and often the best way out for him is to change his place of residence. The success of animals is largely determined by their mobility, and it is not surprising that, with a few exceptions, natural selection has favored the evolution of mobile species.

II. Types of animal movement

There are three types of animal movements: minor movements, migrations and migrations.

Insignificant movements are characteristic mainly for lower animals, which lead a predominantly sedentary lifestyle, moving to a limited extent within a small area. An example is an ordinary saucer, which, at low tide, leaves its place on a rock in search of food, and when the tide approaches, it returns to its place again. Each saucer has its own place on the rock, which has a certain shape.

Migrations are a type of movement of animals caused by the need to get food. The nomadic way of life is typical for the inhabitants of arid and semi-arid regions. If the vegetation is too sparse for a population of animals to constantly feed in a given area, the inhabitants of these places are forced to make long transitions from one feeding area to another. So, moose gather together in winter and move to winter habitats and there, in this limited area, remain until spring. In the warm season, they lead a truly nomadic lifestyle, moving across the vast expanses of the country.

Migrations are regular and directed movements "to and fro". At the same time, characteristic features appear in the behavior and lifestyle of animals. In a number of species, animals migrate several times in their lives, in others - only once (migrations will be discussed in more detail below).

There are no clear distinctions between periodic migrations, migrations and other movements. But all of them are part of the general complex of adaptive properties that ensure the distribution and survival of animals. Migration and nomadism of animals are different. Each species has its own characteristics. In some animals, migrations occur only during the period of family breakdown, when these animals are evicted from their birthplaces, and usually over short distances; for others, migrations are repeated annually in certain seasons of the year due to changes in environmental conditions, while for others, during the years of a sharp increase in the number of species, mass eviction of animals occurs without returning to their birthplaces, and, finally, for fourths, periodic migrations occur during the day, which is associated with their lifestyle and biological habituation. All this greatly complicates the study of migrations, which are of great interest to biological science.

III. Origin of migrations

AT in general terms science knows a lot, especially about the ways of animal migration. However, the causes of their occurrence and the orientation of animals during migration over long distances have not yet been sufficiently studied and are in given time the subject of research by scientists from many countries.

Migrations are characteristic of many mammals, but people know less about them than about bird flights and fish migration. Animals lead a more hidden lifestyle. Observations of them are possible only with special studies.

For centuries, most of the theories that explain migration were based on the most bizarre guesses, often completely wrong. The strange, regularly repeated movements of animals have been of interest to people since the days when ancient hunters first began to follow herds that migrated across the vast savannahs of tropical Africa. On the rocks and walls of caves, such as Lasko, Altamira and Tassilin-Angier, masterpieces ancient painting preserved images of horses, bison and primitive bulls, which served our ancestors for thousands of years as a source of food and other means of subsistence.

Even after the transition to agriculture, people were wondering why some fish, birds and animals are found only in certain seasons and mysteriously disappear at other times of the year, in order to reappear with the same inexplicable regularity after a few months.

In the XVI-XVIII centuries, a number of individuals believed that some animals, in order to avoid adverse conditions coming cold weather, lay at the bottom of reservoirs, and surfaced in the spring. Such a bizarre hypothesis was held by the Archbishop of Uppsala from Sweden, Olaf Magnus, Dr. Samuel Jones (1709-1784), the creator of the modern system of plants and animals, Carl Linnaeus (1707-1778), naturalist Lazzaro Spallanzani (1729-1799) and many others. Aristotle (384-322 BC) put forward a fantastic hypothesis of "transmutations", which explains the seasonal disappearance of some animal species and the simultaneous appearance of others. He even stated that animals were seen directly at the moment of transformation. This myth has survived to this day in some remote rural areas of England. But later, towards the end of the 18th century, the theories became more real, closer to true migrations. The vast majority of biologists, especially in the last century, when "explaining" seasonal transitions, referred to "innate instinct", "generic habit", usually without even putting any specific content into these concepts. Only later, with the development of the teachings of I. P. Pavlov on conditional and unconditioned reflexes, they began to try to formulate the concept of instinct more specifically, in a physiological sense. And, finally, by the end of the 19th century, the migration theory was recognized as proven.

The main reason for migration is the need for food and conditions for reproduction, as well as competition for convenient habitats. When, for example, a herd of buffalo or wildebeest doubles in size, its members are forced to roam over much wider areas in search of food than before. Since fresh grass serves as food for them, the abundant growth of which is associated with a certain season, the movements of these animals also become seasonal. Before the colonization of North America, bison made such trips twice a year, going from Canada to Mexico.

Much less often, migration is driven by the desire to protect oneself from climatic extremes. Even on the islands of the Arctic Ocean, neither musk oxen nor bull-hunting wolves try to move to more warm places. Arctic foxes even move further north at this time of the year to stay close to polar bears and feed on the remains of the seals they have killed. Lemmings and Scottish hare hares also remain to winter in the north, and besides them, other animals and birds. Even the baribal bear does not go south, except perhaps in the most severe winters, when he moves to places where you can safely hibernate without being subjected to such ordeal(if energy resources are overused, he runs the risk of not waking up after hibernation).

Migrations arose in animals in the course of their historical development; they are an interesting biological adaptation. The emergence of migrations is, of course, associated with the evolution of the species to which they are characteristic. They have evolved from the aggregates of animal movements over countless generations. Animals that went in the wrong direction died. Those that chose the right path survived and returned with offspring. At first, there was no need to travel long distances, it was enough just to find an unoccupied territory; but, repeating every year, wandering acquired the character of a stable habit, which eventually grew into an instinct characteristic of the entire population.

Migration ecology arose and is developing as a synthesis of ecology and physiology. This field of study of migration covers a wide range of different aspects migratory behavior. It is very interesting to study the issues of the variability of migratory behavior, the difference in the timing and routes of migration, the individual variability of the migration distribution in time and across the territory in different species.

The migrations probably formed gradually, under the influence of slow climatic changes, such as the retreat of glaciers. With the melting of glaciers, a gradual expansion of areas suitable for food and reproduction began. This reason for the migrations seems more plausible than the assumption that during the millions of years of the Ice Age, animals retained the desire to return to their native lands.

A number of scientists have suggested that some modern migration routes developed against the background of the geographical conditions of earlier eras, and also that as the continents shifted relative to each other, the migration routes connecting the places where the breeding took place, with foraging grounds, lengthened. But migrations could also occur suddenly.

All these ideas do not necessarily contradict each other. The migrations may have resulted from a combination of climatic changes and a series of invasions from various causes. In the case of trans-equatorial migrations, when the territories where animals live in different seasons are separated by a considerable distance, their occurrence is determined by a large number of complex interacting factors. Be that as it may, any hypothesis remains just a guess until it is confirmed by observations or verified experimentally.

The developed form of migration is characterized by a sufficiently high speed and range of movement.

IV. Migrations

Migration, (from Latin migrans) means resettlement. Migrations are widespread among animals of all the globe and are an interesting adaptation for enduring the unfavorable conditions that sometimes occur in nature.

In autumn, as food conditions worsen, the bulk of arctic foxes and reindeer migrate from the tundra to the south, to the forest-tundra and even to the taiga, where it is easier to get food from under the snow. Following the deer migrate to the south and tundra wolves. In the northern regions of the tundra, hare hares at the beginning of winter undertake massive migrations to the south, in the spring - in the opposite direction.

Migrations of animals arise under different conditions and they pass differently.

Regular seasonal migrations of desert ungulates also depend on seasonal changes in vegetation cover, and in some places - on the nature of the snow cover. In Kazakhstan, saigas in the summer stay more often in the northern clayey semi-desert steppes; in winter they migrate to the south, to the area of less snowy wormwood-fescue and wormwood-saltwort semi-deserts.

In general, migrations in mammals are characteristic of a relatively smaller number of species than in birds and fish. They are most developed in marine animals, bats and ungulates, while among the species the most numerous groups- rodents, insectivores and small predators - there are practically none.

Animals have periodic migrations, they are also called eviction. Periodic evictions - migrations include those that represent the mass departure of animals from breeding places without subsequent return to their former habitats. According to science, such evictions are caused by a sharp deterioration in living conditions, as well as lack of food, which is associated with the emerging high population density of the species, forest and steppe fires, severe droughts, floods, excessive snowfall, and other reasons. This shows that numerous circumstances can cause the movement of a mass of animals over long distances. Invasions - the movement of animals outside their homeland. Such movements differ from true migrations in their irregularity and long intervals between successive invasions. Sometimes they are considered as initial stages the formation of real migrations arising from explosive settlements - "emigrations". Invasion is like a safety valve triggered by excess population density. In itself, this favors the existence of the species only indirectly. Under normal natural conditions, population processes are in equilibrium, and population growth resulting in eviction rarely occurs. Invasion is a phenomenon, the disadvantages of which are striking, but which, at the same time, for a long time gives an advantage that more than outweighs the disadvantages. A typical example of these migrations is the migration of lemmings and squirrels. Irreversible periodic migrations are characteristic of ordinary proteins. They (migrations) arise quickly in response to unfavorable conditions. Migration begins in July-August, when the squirrels begin to feed on seeds and nuts of a fresh crop and discover their deficiency. Migration continues for about 6 months. Squirrels sometimes overcome up to 500 km or more. Proteins do not migrate in groups, but singly. Squirrel wanderings are periodically repeated every 4-5 years and greatly affect the yield of furs and the economy of squirrel hunters. The speed of squirrels during migration reaches 3-4 km/h.

seasonal migrations animals commit annually and in certain time of the year. These migrations are regular and reversible. Animals, leaving their breeding places, return to the same places when favorable conditions occur. Seasonal migrations are characteristic of Arctic fox, the main reason for which is food. Arctic foxes follow migrating lemmings, completely repeating the properties of their migrations. The migration of predatory animals is mainly associated with the migration of small animals that are food for predators.

Seasonal migrations are especially pronounced in places with a sharp change in habitat conditions from winter to summer, in places with severe winters and hot, dry summers. This phenomenon has the character of a purposeful mass movement, although it is not always clearly visible. The causes of seasonal migrations are always complex. However, the most tangible of them is hunger. Another reason is the attack on animals by gnats: mosquitoes, gadflies, horseflies.

Seasonal migrations, in turn, are divided into horizontal and vertical.

Horizontal migrations are those when animals move from one place to another, changing environmental conditions within their typical landscape. Such migrations are typical for reindeer, seals and other animals.

Vertical migrations are understood as those when animals in the same season of the year find the best conditions for themselves in the spring in high-mountain regions in alpine meadows, and in autumn they descend to the foothill pastures. Such movements are typical for the inhabitants of the mountains - goats, chamois and other ungulates. Mountain ungulates by the summer rise to the upper mountain belts with their rich herbage, in winter, as the depth of the snow cover increases, they descend. And in this case, some predators, such as wolves, are observed combined with ungulates.

Diurnal migrations are also known among animals - this is the transition of animals from places of daytime haulouts to places of watering places, salt licks and feeding. Daily migrations are characteristic of hares, deer and other animals.

All the aforementioned migrations are called active because the animals carry them out with great excitement, they sometimes appear in settlements and in other places that are not typical of their habitat and often, unfortunately, remain unaccounted for.

In contrast to active migrations, passive migrations are also observed among animals, that is, those when animals move away from their breeding grounds and their usual habitat with the help of ice or water currents. For example, migrations of walruses, polar bears, and arctic foxes are known, caught on ice floes, which were carried away by the current into the ocean to some islands. Hares and muskrats during floods, falling on floating objects or ice floes, go downstream for long distances. Different modes of transport play a significant role in passive migration. The distribution of mouse-like rodents through vehicles is especially characteristic. As a result of passive migrations, house mice, rats and other animals were settled almost all over the world. Many of the introduced species of animals get along well in new places. Thus, there is an increase in the range of certain species of harmful rodents.

Rodent migrations are of interest in the sense that many of them can be used in hunting and fishing and in pest control. Agriculture.

V. Orientation of mammals

Since migration is one of the forms of development of the surrounding space, not a single creature, who does not have the ability to orientate, is unable to master this space, cannot move in it in an ecologically expedient and useful way. And if this is so, then, consequently, the evolution of migratory behavior went, first of all, through the improvement of the ability to navigate in space. But if migration is impossible without orientation, then the ability to navigate in space, of course, goes beyond the limits of migration tasks, ensuring the existence of a living organism in the surrounding world. The ability to perceive objects and phenomena of the environment and on this basis to create an idea of their location in space is inherent in all animals and accompanies any animal organism from the moment it is born until death.

The ability to navigate correctly is vital for all creatures, but it is especially important for migratory species. As a rule, they use noticeable landmarks, and then the ability to find the right direction by the sun, moon or stars is not so necessary, becoming a valuable help in critical situations, and in cases where travel is made over very long distances. An assistant in the orientation of animals during migration is not a mysterious "sense of direction", but vision, memory and a sense of time.

The behavior of mammals differs from the behavior of birds and lower animals, primarily in that in mammals learning plays a greater role than instinct. Therefore, among mammals, the ability to navigate by the position of celestial bodies is much less common, although many species have been specially studied to identify such abilities. However, scientists have found that field mice, which are also active to some extent during the day, orient themselves by the sun. It is very likely that in large mammals, young animals can simply remember the path to follow during migration, learning from parents and other members of their community, and then pass on the knowledge to the next generations. The assumption that the sense of smell plays a certain role in orientation in mammals has been experimentally confirmed only at the very beginning. recent times, and here we may be on the verge of interesting discoveries.

Smells and smell play a huge role in the life of animals. Smells are vital necessary information from the surrounding world, excite instincts, conditioned reflexes, determine a positive or negative attitude to new environmental factors. The sense of smell is one of the oldest and most important senses, with the help of which animals orient themselves in their environment.

VI. Ways to study migrations

Methods for studying mammal migration are varied and complex. This is primarily due to the fact that mammals live in different environment. Some of them live in terrestrial conditions in the forest and on the ground or in the crowns of trees. Many of these animals have excellent climbing ability. Other terrestrial animals inhabit open spaces and have a fast run, or when danger arises, they instantly hide underground (marmots, ground squirrels); some of the mammals (desman, mink, muskrat, nutria, etc.) semi-aquatic image living near rivers where they forage for food.

In recent years, special attention has been paid to migration by scientists around the world. Migrations began to be studied not only through direct observations, but also with the help of marking. Already, the marking of many terrestrial animals gives an interesting result and forces us to reconsider previous theories about their geographical distribution. Marking is a more accurate and objective reflection of migrations occurring in nature.

Marking of animals began to be used in 1924. At the beginning (in 1924-30) only 22 animals were tagged: 19 hares, 2 chipmunks and 1 bat. These were uncertain steps in the new interesting case. In the future, animal tagging began to be introduced everywhere, and after 30 years 16,693 animals belonging to 75 species were tagged.

V. S. Pokrovsky, an employee of the Commission on Environmental Protection of the Academy of Sciences of the USSR, noted back in 1959 that this type of research in our country is far behind others, since the method of trapping and marking mammals is still poorly developed.

At the first stage of development of tagging, fur-bearing animals were tagged the most. Of the 16,693 goals looped between 1924 and 1955, there were 11,248. Very few ungulates and mouse-like rodents have been tagged, although their migrations are of great scientific interest. When comparing the development of animal ringing and similar work on birds carried out over the same period, it can be said that the results obtained on mammals are insignificant.

Marking animals is a tricky business. Caught live animals are usually very aggressive. Currently, scientists are testing various drugs that temporarily put animals to sleep, especially large terrestrial ones, so that they can be used for various manipulations during tagging. This idea comes from the experience of hunters in many tribes of the Southern Hemisphere, who used poisoned arrows for hunting. A drug called curarediplocin has already been created, which has a strong effect on the muscles of the animal, temporarily relaxing it. The use of this invention can facilitate the mass marking of deer, kulans and other ungulates and intensify the study of the migrations of these animals. Various approaches to labeling are also determined by the morphological features of mammals. Terrestrial animals have auricles, which are intensively used for marking. Underground and water do not have them.

Labeling methods:

Tattoo. The ear of the animal is preliminarily wiped with alcohol, then a number is put with tattoo forceps and ink is rubbed into the puncture sites, which is usually well preserved.

Ringing. For animals that do not have an auricle (muskrat, shrew), the ring is put on the hind leg, above the foot.

Notches or perforations. Special tongs make marks on the ears and webs of the paws, giving each mark a conditional numbered value. Used in the study of semi-aquatic animals (mink, otter).

If ringing is carried out on a large scale, then this method allows one to draw some conclusions about the total stocks of game in a given area, since the number of all individuals killed by hunters should be approximately the same percentage of the total number of this game in a given area, which and the percentage of prey of ringed individuals to the number of rings put on: a / b \u003d x / c, where a is the number of ringed birds, b is the number of returned rings, c is total species taken by hunters.

The methodological difficulties in studying the migrations of animals lie in the fact that they are, to varying degrees, accessible to direct human observation, due to a secretive way of life; usually all animals, when meeting with a person, quickly leave and a long, direct observation of them in natural conditions almost impossible.

We know a lot about the migration of animals from the works of Russian travelers of the 18th century, academicians I. Lepekhin, P. Pallas and the 19th century A.F. Middendorf and others. During their travels, they paid great attention to the migration of animals.

To clarify the directions and routes of migration, the return of marks or the message about the mark of the hunted animals is important.

Tagging is an important scientific method for studying migrations.

VII. Migration Alternatives

Although migration is an integral part of the life cycle of many animals, it is nonetheless just one way to avoid exposure to adverse environmental conditions. There are many animals that do not make any migrations and have developed other ways in the process of evolution to survive the harsh season.

The adaptations of mammals to survive periods of the year that are unfavorable in terms of food and weather are more diverse and perfect than those of lower classes.

By winter or a dry summer, reserve energy substances accumulate in the body, helping to survive the difficult season. In addition to the accumulation of glycogen in the liver, many species become fat to some extent. For example, a small ground squirrel with a vein has a mass of about 100 - 150 g, and in the middle of summer - up to 400 g. In a marmot marmot, subcutaneous and internal fat in June is 10 - 15 g, and in July - 250 - 300 g, and in August - 750 - 800 g. In some individuals, up to 25% of the total body weight is fat.

The next seasonal adaptation is hibernation, which is characteristic of many animals from the orders: monotremes, marsupials, insectivores, bats, edentulous, predatory, rodents. There are no hibernating species among those orders that are most characterized by seasonal migrations: cetaceans, pinnipeds, ungulates.

Hibernation may be a direct and immediate response to adverse external conditions, in which case the awakening occurs shortly after conditions change for the better. But for many animals, hibernation is a state of physiological dormancy, or "diapause." The stay of the body in this state is under constant hormonal control, and awakening does not depend directly on the onset of favorable conditions.

Diapause is associated with the course of the "biological clock", and its onset is a reaction to a change in the length of the daylight hours, or photoperiod. Thus, falling into diapause can be caused by events preceding the onset of unfavorable conditions, i.e., it is a kind of adaptation to them.

Hibernation in mammals differs from diapause in that it is interrupted by periodic short-term awakenings. At the same time, animals safely overwinter without any food, consuming a minimum of fat stored for future use. Body temperature is maintained at one degree (Celsius) and fluctuates between 5-15 ° C. The awakening of the animal shows that the temperature has gone beyond these limits.

According to the degree of hibernation, there are two main options:

Seasonal sleep, or optional hibernation. In this case, body temperature, the number of respiratory movements and the overall level of metabolic phenomena are reduced a little. With a change of scenery or with anxiety, sleep can be easily interrupted. It is typical for bears, raccoons, raccoon dogs, and partly for badgers. At polar bear only pregnant females and immature ones lie in the den. Brown bears and badgers do not hibernate in the southern parts of their range. On the condition of the American black bear sleeping in winter, the representations provide such data. At an air temperature of - 8°C, a temperature of + 4°C was noted on the surface of the skin, in oral cavity+ 35° (against + 38° during wakefulness). The number of breaths was reduced to 2 - 3 per minute (against 8 - 14 when awake). The terms of occurrence in winter sleep and its duration are variable not only geographically, but also over the years. There are cases when, during thaws, especially in low-feed years, raccoons, raccoon dogs and brown bears leave their shelters and lead an active lifestyle.

True continuous seasonal hibernation. It is characterized by a loss of the ability to thermoregulate (a state of heterothermia), a sharp reduction in the number of respiratory movements and contractions of the heart muscle, and a drop in the overall level of metabolism. Along with hibernation there is also summer hibernation, also caused by the seasonal deterioration of the food supply. Most often, it is observed in rodents deprived of a full-fledged and water-rich food in the summer. These are mostly gophers. The yellow, or sandy, ground squirrel hibernates the earliest. Central Asia(in June - July). In ground squirrels, summer hibernation usually passes into winter without interruption. Summer hibernation is also observed among the inhabitants of the tropical zone. Senegalese hedgehogs hibernate in summer for three months.

The physiological mechanisms of hibernation have recently been intensively studied. Diapause, being a genetically predetermined state of inhibited development and induced by the length of daylight hours, is an important adaptive mechanism that allows animals to survive not only periods of unfavorable climatic conditions, but also periods of lack or scarcity of food supplies. Indeed, one of the main features of seasonal lifestyle changes is their relationship with food supply: the life cycle of animals is synchronized with the rhythm of their natural food sources. The significance of the reaction to changes in the length of daylight hours is that appropriate adaptations to the change of seasons can occur before the onset of frost, drought or starvation leads to a complete cessation of all activity. The state of diapause is usually characterized by a temporary cessation of growth and reproduction, a decrease in basal metabolic rate, and often an increase in the ability to withstand climatic conditions such as heat, frost, or drought, as well as other morphological, physiological, and behavioral features. This phenomenon is widespread among various living beings.

The trigger mechanism for the migration of species to which it is characteristic is a change in the length of daylight hours. A significant role in the seasonal migrations of animals associated with reproduction is played not only by the signals received with the help of sight and smell, but also by gravity, which is used for orientation in areas with sharply changing topography, where reproduction occurs at the bottom of gorges or in valleys. There are countless examples showing that the migration of a huge number of mammal species in the zones temperate zone largely controlled by daylight hours, which is a more reliable indicator of seasonal changes throughout the year than any other climatic factor.

Another (new, compared with the previous classes) main adaptation that ensures the survival of unfavorable seasonal living conditions is the gathering of food supplies. It is characteristic to varying degrees of different systematic groups of mammals. Classical nomads do not store food - nomads: cetaceans, pinnipeds, ungulates and hibernating mammals. The burial of excess prey in carnivorous animals is more common. Weasels and ermines collect 20-30 voles and mice each, black polecats pile several dozen frogs under the ice, minks - several kilograms of fish. More large predators(martens, wolverines, cats, bears) hide the remains of prey in secluded places, under fallen trees, under the stones. Leopards often hide part of their prey in the branches of trees. A characteristic feature of the storage of food by predators is that no special pantries are built for its burial, only one individual that built it uses the stock. In general, stocks serve only as a small help for experiencing a low-feeding period, and they cannot prevent a sudden onset of starvation. Characteristic features of stockpiling are the multiplicity of stocks that provide animals with food during the hungry period, the arrangement of special storage facilities for stored food and its collective, often family consumption. Feed is also stored by a few species of animals that hibernate for the winter. Such are chipmunks and Siberian long-tailed ground squirrels. The food collected in the places of hibernation is used by these species in the spring, when the awakened animals are not yet provided with newly appeared food.

Obviously, migration should be considered as one of the forms of strategy, through which various animals respond to seasonal or irregular changes in their living conditions that affect them. living space, reproduction and the need for food. Be that as it may, the instinct that prompts migration is inherent in many animals. At the same time, the process of evolution leads to numerous compromises, and along with the benefits, migration also has a downside. In particular, migratory animals, being away from relatively safe places where they spend most of the year, are more vulnerable to their enemies, especially humans. Accumulating on migratory routes, animals become objects of barbaric destruction. Wild animals do not recognize borders between states. The problem is not only to limit the activity of professional and amateur hunters. The delicately balanced process of migration can also be disturbed in cases where, as a result of the development of agriculture, forestry or mining, animal habitats are modified. The migratory animals of the African savannah are especially vulnerable. So, for example, elephants are in relative safety only in the territory national parks, where they are protected from poachers, but outside the reserve everything turns out to be against them. And the point here is not so much that they cause great harm to farms and plantations, but that they are a source of valuable cape and ivory. And by blocking the migration routes of elephants, human settlements severely limit their distribution. national parks, where excessive eating by elephants of vegetation and subsequent soil erosion often occur.

On the whole, it should be taken into account once again that the adaptation of mammals to the experience of seasonal unfavorable living conditions is more diverse and perfect than that of other vertebrates. Gathering food stocks deserves special attention.

Recently, it has been found that migrations are also characteristic of individual populations inhabiting a particular geographical area. These migrations occur within the range - the area of distribution of the species. They are an integral part of the vital manifestations of the species and a side evolutionary development his.

Ungulate animals are an important object of hunting. They give excellent meat and leather, which goes to the suede used in the leather and haberdashery industry. In order to rationally exploit the natural reserves of ungulates, the study of their migrations is of great interest. Seasonal migrations of ungulates occur not only on the European-Asian continent, but also in Africa, in a country with a warm climate. The main reasons for them are climatic factors.

Hares have 3 types of migrations: - periodic, when under the influence of population growth and the emergence of unfavorable living conditions, a mass eviction of hares occurs; - seasonal - these are regularly repeated evictions in the tundra, caused by starvation in winter time; - daily allowance, determined by the movement of animals from places of daytime haulouts and feeding places. In the taiga, you can find entire trails on the moss, along which hares make their daily transitions.

Ungulates are characterized by three types of migrations: - regular; - seasonal; - per diem. Seasonal migrations are longer and they take place over long distances, sometimes up to 100 km. Well expressed in reindeer. In spring and summer, they go from the forest zone to the tundra, to the Arctic Ocean, and back in winter. Their speed exceeds 15-20 km/day.

In some cases, migrations expand the geographic range of a species.

VIII. Specific examples of animal migration

First of all, the distribution of animals is influenced by climatic conditions, among which the main factor is the temperature of the habitat. Different types of animals have different ability to withstand temperature changes. In some species, this amplitude has a wide range, while in others it is very narrow. The requirements for the temperature of the habitat lead to the zonal distribution of animals.

In Africa, to the north and south of the equatorial climate, subequatorial, tropical and subtropical climate zones follow. The average monthly temperature in summer is about 25 - 30. In winter, high positive temperatures also prevail (10 - 25), but in the mountains there are temperatures below 0. The greatest amount of precipitation in equatorial zone(average 1500 - 2000 mm per year). To the north and south of the equator, precipitation decreases.

The air temperature is constant here. Throughout the year, it fluctuates between +24 and +28. On land, precipitation exceeds evaporation. The soil becomes swampy, thick and high wet equatorial forests. In the Serengeti, animals undertake migrations 300 km long. From May to August, when it rains, ungulates, breaking up into separate large groups, migrate to the south, because most of the pastures at this time turn into swamps. In November-December they return back. Seasonal migrations of ungulates occur not only on the Euro-Asian continent, but also in Africa, in a country with a warm climate. The main reasons for them are climatic factors. When the rainy period begins in tropical Africa, semi-deserts and steppes come to life with their xerophytic flora (plants of arid habitats), temporarily covered with a bright carpet of spring greenery and flowers. Then migrations of mammals occur on free pastures. The beasts leave the sublime mountain steppe and the desert. Numerous herds of antelopes, zebras, gazelles and other ungulates are followed by large predators: lions, leopards and their cowardly companions - hyenas and jackals. When the rainy period ends and the plain burns out under the scorching sun, there is a reverse migration of animals.

Any species can establish itself in a new place and under new conditions, if there is enough free space or there is an unoccupied ecological niche in the ecological system, or if it has an advantage over another species that has previously established itself here and is able to displace it. In different parts of the world there are comparable ecological niches that can be occupied by species that are not even distantly related to each other.

Surprisingly, the sphere of wandering of domestic reindeer in Scandinavia is much wider. This is not only about limited movements, which are mandatory for all herd herbivores. Sometimes summer and winter pastures are separated by more than 250 km of difficult path, and the initiative of the transition belongs to the reindeer themselves, and not to their owners.

Asia and North America, on the contrary, are characterized by huge wandering herds of deer, which, obeying instinct, regularly set off. Neither rivers nor lakes stop animals. And often at crossings and on mountain passes, where deer accumulate in huge numbers, local hunters are waiting for them and arrange bloody slaughters. Migrating deer reach Novaya Zemlya. In their footsteps on the ice, the previously unknown Bolshoy Lyakhovsky Island (Novosibirsk Islands), almost 60 km away from the mainland, was discovered.

Lemmings: These small, predominantly nocturnal rodents inhabit the plateaus and mountain slopes of the Scandinavian Peninsula. For a number of years, there may be very few lemmings in the area, but then there is an explosion of reproduction, as a result of which a myriad of these animals appear. Such periods are known as "lemming years". The reasons for such jumps in numbers are not yet fully understood, but the following can be assumed: at certain times of the year, some group of lemmings falls into exceptionally favorable conditions; a direct result of this is a rapid increase in the frequency and size of the litter. If such conditions persist for a number of years, there is an exorbitant increase in the population. But no matter how abundant food supplies are, after about 3-4 years there comes a moment when local resources are exhausted, and then mass emigration of the excess population begins. These emigrations are an impressive sight: thousands and even millions of lemmings set off in search of food. Contrary to popular belief, they start the journey not large groups, but one by one. But when some natural obstacle, such as a river, is encountered on their way, countless hordes of lemmings are constantly concentrated on its banks. Sooner or later they throw themselves into the water and drown by the thousands in futile attempt swim across the river. The last act of the drama comes when the lemmings, having overcome all obstacles, reach the sea. Here, on the shore, a huge number of animals gradually accumulate, and the pressure of this living mass becomes so strong that they begin to rush into the water. A few lucky people get to the nearest island, the rest drown. And although we are now slowly beginning to understand the laws by which the suicidal emigration of lemmings occurs, it still represents one of the most exciting and thought-provoking phenomena of nature.

In those days, when human settlements had not yet stood in the way of ungulates and the possibilities of their movement were not limited to the territories of reserves and protected areas, the herbivores of East Africa annually made their seasonal migrations, crossing mountain ranges, crossing rivers and fording swamps to reach the green savannah. during the rainy season or return to the forests with the onset of drought. In recent years, settlements and agricultural land have had an extremely negative impact on the lives of wild animals, blocking their migration routes and forcing animals to be content with relatively small areas, which often result in overgrazing and soil erosion. These areas, where many species of large African animals are now preserved, may represent the remains of lands that lie on the path of past migrations.

Huge herds of caribou stay in one place only during the birth of young animals, only about 14 days. The path of the caribou as a whole can reach 1000 km, but the northern Asian deer, yielding to the American ones, sometimes still go more than 500 km. The reasons for migration can be very different. The main role, of course, is played by the forage of the land and the weather. Mass attacks of mosquitoes, gadflies and gadflies, which cause unbearable suffering to deer, can also become an immediate reason for the start of migrations.

In addition to local movements over a more or less limited area, some mammals undertake much more distant travels during the breeding season. A classic example is the Arctic caribou, which cover distances of 650 to 800 km annually. All summer they graze in the tundra, but with the onset of July, they set off on their way to the south, through coniferous forests following the same routes. In other places, the hooves of thousands of animals that passed here one after another during an endless series of annual migrations made a path up to 60 cm deep in the stony ground. Equally large herds are characteristic of herbivorous animals of the steppes and savannahs. Males sometimes cluster in dense groups of 100 to 1000 heads, but such clusters of animals of the same sex are not stable, since mating occurs during autumn migration. In wintering places, caribou remain until the arrival of spring, and then set off on their way back to the north. On the way, deer are born to them, but even this cannot delay the herd for a long time. It rushes forward, regardless of any obstacles, and it happens that during crossings through deep rivers many deer drown. In one such place, 525 corpses of dead animals were found.

Before, when the bison were still very numerous on the American continent, they undertook their impressive trips, moving in a more or less closed circle, so that in winter the herds sometimes found themselves 650 km south of their summer pastures. Unlike bison, wapiti deer are much less prone to travel. Their movements are reminiscent of the vertical migrations of bighorn sheep, black-tailed mule deer and moose, which forage all summer high in the mountains, and as winter approaches, they descend into more sheltered valleys where the snow is not so deep and food is easier to obtain.

There was a time when African elephants made long-distance migrations in order to provide themselves with a suitable shelter at the right time and throughout the year to have a sufficient variety of food, water and the salt they need. During such migrations, herds of elephants received a convenient opportunity to regroup, and at times it happened to observe large, up to 100 heads, accumulations of animals. These migrations were of two types: during the rainy season, elephants roamed randomly from place to place over a limited area, but, in addition, every year they made directed migrations, passing many hundreds of kilometers. In different seasons, elephants prefer different habitats: in the rainy season they stay in open spaces, and in drought they hide in the forests.

The large mammals of the savannas can be divided into three groups based on their need for water.

The first category should include animals that constantly need water, such as the hippopotamus, which requires habitats where there is always enough water. However, this requirement does not prevent hippos in the event of drought or local overpopulation from making tedious land crossings from one river to another.

The second category includes species that have adapted to an arid climate. The need for water in such animals is very limited. For drinking, they either use surface water, or are content with the moisture contained in the succulent parts of plants, the roots of which go deep into the ground. Rhinos are such partially adapted to dry climate and non-migratory mammals.

The third category includes animals migrating or partially migrating in search of water. Among the representatives of this group, African elephants are in the first place, followed by buffaloes and, finally, predators such as lions, cheetahs, hyena dogs and hyenas, as well as the insectivorous earthen wolf, honey badger and Kaftian fox.

Every year between Kenya, southwestern Ethiopia and Sudan there is a massive, albeit little-studied, migration of animals. It begins in May, when the water level rises in the swamps of the upper Nile, and then the animals rush in a southeasterly direction to the arid regions on the border of Kenya. The roar of countless herds of antelopes that close the horizon is like the noise of a cavalry army on the march. The bulk of the animals are white-eared kobs, tyangi bubals and mongalla gazelles. Lions and smaller predators accompany migratory animals along the flanks.

In the past, the valleys of southern Ethiopia and northern Kenya teemed with a variety of animals by the end of July. The number of species of ungulates making their perilous journeys south was not in the hundreds, but in the thousands. Although the desert of Turkana blocked their way, this did not prevent them from spending three or four months here in contentment, until the need for fresh food prompted them to set off again to the north, where life-giving rains had already revived vegetation. By September, these places were empty again. In huge columns many kilometers long, the animals slowly and calmly left to the north, protecting the young from voracious predators, and the valleys again burned out under the scorching rays of the sun. Herds of oryxes and Grant's gazelles, scattered by migration over vast distances, again returned to their father's house. It was possible to drive for a long time through the area, on each square kilometer of which hundreds of antelopes graze, and then suddenly cross a sharp but invisible border, beyond which, for no apparent reason, you will no longer meet a single animal. One such boundary of such boundaries lay to the east of the Loile airfield. At the peak of the migration there were more than three thousand antelopes, while a few hundred meters to the east one could spend many days in a row without meeting a single animal.

When the dry season begins in June or July, thousands of wildebeest leave the Serengeti on their 320-kilometer journey west towards Lake Victoria, and return when the rains revive the parched pastures. Here you can still meet huge herds of herbivores (zebra, African buffalo and antelope of many other species), accompanied by various predators (leopards, lions, cheetahs, hyenas, hyena dogs and jackals). Most of these migratory animals limit their stay in dry areas while seasonal or occasional rains fall. In order to survive, they have to migrate between areas where they can graze during the wet and dry seasons.

Nomadism also has its downsides. Although newborn cubs of ungulates are more highly developed and mobile than the blind and naked cubs of most other mammals, nevertheless, even they usually remain motionless for several days or weeks after birth and hide in case of danger. In probably no more than 40 out of 185 different ungulates, the young follow the mother immediately after they get to their feet. The methods that help lurking young to remain unnoticed are similar even in completely unrelated species. Cubs that follow their mothers are less helpless than lurking ones and are more at risk of being attacked by predators. Species whose young accompany their mothers and flee from predators live in open spaces where they lead a nomadic or migratory lifestyle.

IX. Conclusion

The significance of migrations lies in the fact that they affect the dynamics of the number of animals and affect commercial interests. different countries. In order to rationally use the world's reserves of one or another species of terrestrial mammals, one must know their migrations.

In the vast field of research related to animal locomotion and orientation, each new discovery raises new hypotheses and new questions. Only a few decades ago, both of these phenomena were shrouded in mystery to such an extent that hypothetical forms of extrasensory perception sometimes invoked hypothetical forms of extrasensory perception to explain them. Today, all hypotheses relating to these phenomena are based on observations and experiments. Although much remains to be discovered, we already know enough to understand the general routes of animal migration, the time when they occur, and the methods of navigation used in this. We also know the degree of risk that migratory animals expose themselves to. Therefore, nothing can justify us if we do not use this knowledge. The mystery has not yet been solved, although science has a lot of information about migration.

At present, the evolutionary role of migration remains one of the tasks that have not been solved by science.

When a person is able to solve one of the greatest secrets nature - the secret of animal migrations on our planet, we will discover such relationships between living organisms and the Universe that we do not even suspect now.

The economic importance of migratory animals has increased significantly and continues to grow. Of no small economic importance are changes in the migration of commercial fish, birds and mammals, caused by the construction of dams and reservoirs, railways and pipelines, the plowing of virgin lands, the construction of cities and factories. All these questions are currently the subject special attention scientists and manufacturers.

In some cases, animal migrations lead to completely unexpected consequences for humans. Thus, at present, more than 4,000 aircraft in the world annually collide with migratory birds and receive serious damage. In addition, migratory birds carry arboviruses that cause severe infectious diseases people and farm animals. bumping into power plants and power lines, arranging nests on them, resting during migrations, birds cause severe power outages, accompanied by significant losses of electricity.

Bibliography

Akimushkin I.I., "Where? and how?"; M.: 1965 - 380 p.

Blon Georges, "Great Camps"; M.: 1982 - 158 p.

Darlington F., "Zoogeography"; M.: 1966 - 518 p.

Zenkevich L. A., "The Life of Animals"; M.: 1971 - 627 p.

Ilyichev V. D., “Vertebrate Zoology”; M.: 1976 - 288 p.

Cloudsley-Thompson, D., "Animal Migration"; M.: 1982 - 136 p.

Korytin S.A., "Behavior and smell of predatory animals"; M.: 1979 - 224 p.

Sokolov V. E., "Ringing and marking"; M.: 1987 - 160 p.

Fateev K. Ya., "Migrations of animals"; M.: 1969 - 72 p.

Shevareva T.P., “Migration of birds and mammals”; M.: 1965 - 163 p.

Material from the Uncyclopedia

Scientists call animals moving over long distances migrations. Travel all insects, fish, reptiles, amphibians, mammals, birds. Migrations are periodic - regular - and non-periodic.

Regular travel of animals is usually associated with seasonal changes in nature. The onset of cold weather in countries with a temperate or cold climate or heat, followed by droughts in the steppes, deserts and semi-deserts, deprive many animals of food, and they move to places where food is available at that moment. The life of some animals is associated with the harvest of certain feeds, such as seeds coniferous trees. In years with a poor harvest of squirrel seeds, the nutcracker, crossbill, sable, marten, bear leave their inhabited places and move to other areas. These are irregular migrations.

There are also catastrophic migrations, when habitat conditions change dramatically. They broke, for example, an old house, and everyone who lived in it - birds, mice, insects - set off in search of a new haven.

Sometimes migrations take a very long time. Salmon fish fry, having left the eggs, grow up a little and go down the rivers to the sea, and from there to the ocean. It will be several years before they return to their native lands to spawn. In some northern gulls, chicks, until they become finally adults, capable of breeding their own offspring, roam the southern countries for several years.

Famous for their migrations river eels. On spawning from the rivers of the basin Baltic Sea eel goes to the shores of America, to the Sargasso Sea. The hatched larvae, gradually growing up, make their way back. If you measure it in a straight line, then it will be 8 thousand km.

Some birds cover even greater distances during migrations. Arctic terns from the shores of the Arctic Ocean fly over 17 thousand km to Antarctica. Even our common starling, ringed on curonian spit, managed to fly to Belgium in a day, for 1230 km. Fans of such long journeys are among the insects. Once in Africa, butterfly migrations were observed that lasted 4 months. Dragonflies, butterflies and ladybugs fly over mountain ranges, oceans, suddenly appear in huge flocks in the most unexpected places.

The speed of movement of animals during migrations is amazing. A ruby hummingbird weighing only 3.5 g flies over 900 km in 25 hours Gulf of Mexico, making 50 wing beats per second. Some birds make their non-stop flights for 105-115 hours. Fat reserves in the body, which have a very high calorie content, serve as a kind of "fuel".

Some species prefer to travel during the day, others at night, and some both during the day and at night.

What draws them to distant and dangerous wanderings? There are various assumptions. The most common of these is the desire to avoid adverse conditions: cold, heat, drought and associated famine.

Mass movements of animals, probably, took place over many geological epochs, gradually becoming fixed in their "memory" from generation to generation. It could have been different. Once, many millennia ago, the climate of our planet was different, the ancestors of modern animals lived in southern countries, and descendants annually return to their native places. True, observations have shown that the changes introduced by man into nature: the creation of new reservoirs, the reduction of forests, etc., affect the migrations of animals. The old ones disappear, new ways, places of stops, winterings, habitats appear.

How do animals navigate, unmistakably find their way?

Not all the sense organs of animals and their capabilities are known to people yet. Animals are able to navigate by the sun, stars, having a "compass" unknown to us. An internal, highly accurate biological clock allows them to correct for the "compass". Animals catch and use favorable winds, currents, magnetic and gravitational fields of the Earth, they are able to feel the slightest changes in barometric pressure. They keep in mind detailed map terrain and the most noticeable objects on it. Many people use their sense of smell to find their way. Pigeons perceive polarized and ultraviolet radiation, hear infrasonic noises at ultra-low frequencies of long waves. Bats use echolocation. Locators are used by many aquatic animals - whales, fish. The locator successfully replaces the organ of vision with them. Wasps, honey bees memorize voluminous objects well, pointing them in the direction. Fish have a very sensitive sense of smell. For most of them, it serves as the main pointer for migrations. This is how salmon and other migratory and semi-migratory fish find their way to their native rivers.

You can also conduct various experiments in your circle and at the biostation for the study of animal migrations, take part in the work of scientists, completing their task. The one who will be able to unravel the secrets of animal migrations, their "navigation instruments", will make one of the largest scientific discoveries.

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Seasonal animal migrations are one of the most impressive phenomena in nature. Birds are the most avid travelers in the animal world. Half of all bird species fly long distances to places where there is a lot of food or where they can hatch chicks. Huge flocks or herds, as if on command, are removed from their place and set off on a journey hundreds and thousands of kilometers away.

Migration can be caused by the need to search for food, the lack of which is due to natural causes. In much of Africa, for example, during a drought, the grass dries up completely, and wildebeest and zebra are forced to go in search of new fresh pastures. They return later. However, not all animal migrations are so impressive. Some animals living in the mountains simply descend from the mountains a couple of hundred meters into the valleys in autumn, and again rise to the mountains in the spring.

In addition to seasonal migrations, there are also so-called animal migrations common among cicadas and lemmings. This happens when the number of animals begins to exceed the food reserves available in a given habitat, and part of the population is forced to go in search of a new habitat.

Antelope - jumper

For the appearance of Europeans in Africa, the jumping antelope paid quite a lot. In the 19th century in poor areas South Africa millions of these antelopes grazed. In dry times, when there was no more grass left on the pastures, the antelopes went in search of water and food, overcoming great distances, but when Europeans appeared and began to develop these lands, the antelopes were no longer able to move freely. The end of their migrations has come. Now in Africa, these antelopes have survived in much smaller quantities.

Arctic Terns

Arctic terns hatch chicks in the far North (sometimes beyond the Arctic Circle), where they feed on fish, diving into the sea after it. After the mating season, arctic terns travel to the other side of the world to spend the winter on the pack ice in Antarctica. Here they use the same hunting tactics as in the North, feeding on small fish that swim close to the surface of the water. In order to live in daylight all the time (which allows them to fish around the clock), the tern travels twice a year from one pole to the other. Every year this little bird covers a distance of 32,000 km. Cruising from the Arctic summer to the Antarctic, she spends a noticeably larger part of her life in daylight than any other creature. Some terns, on their migrations, cross Atlantic Ocean.

Butterfly flight

During the summer, the caterpillars of the monarch butterfly feed on poisonous plants from the gossamer family that grow in Canada and the United States. The poison accumulates in their body and then passes into the body of butterflies, which fly south in huge swarms in autumn. In the spring, they return again, with females laying eggs along the way.

Migrations of animals in the steppes of Central Asia

Saiga (saiga) - an antelope with a bizarre thickened nose - has been living in the steppes of Central Asia for 20,000 years. Male saigas have horns, which they use in battles for females. Each male gathers around him from 5 to 15 females and protects them from other males. In winter, when the cold winds begin to blow and the northern regions are buried in snow, thousands of saigas head south in search of new pastures. They return in the spring. Their movements are closely watched by other animals. The eagles try to attack the young calves, and the wolves feed on the placenta of the females.

During the last ice age, saigas occupied the territory from England to Eastern Siberia. At present, they remain only in the steppes of Central Asia. Until recently, they were even endangered. Fortunately, the efforts made to save them were successful. Now their number has increased, and they can continue seasonal migrations. They are perfectly adapted to the environment. Saigas belong to artiodactyl animals and on thin legs they can move at high speed across snow-covered steppes. An adult saiga reaches 75 cm in height. In summer, the fur of the saiga is short, light brown; in winter it becomes very thick and brightens somewhat.

Graduation work

Performed by Viktor Tkachenko

Secondary school - Lyceum No. 265

St. Petersburg

I. Introduction

The entire animal world of the planet is in constant motion: from the smallest planktonic organism to giant whales in the seas and oceans, from tiny midges to huge albatrosses in the air, from such small mammals as lemmings to elephants - everything moves, everything moves in the surrounding space , looking for the best habitats, rich in food or convenient for reproduction. Some animals make their movements irregularly, others strictly cyclically: once a day, a month, a season, a year, or even once every few years. For some inhabitants of the planet, such a journey is the only one in life, while others undertake it many times. It is as if a gigantic pump, or rather a multitude of pumps, pumps the animal population of the planet, mixing it and directing it along one or another channel.

Animal movements are strictly limited in space and time. They follow certain rhythms. It would seem a contradiction: on the one hand, constant movement, on the other hand, binding to certain points in space, certain routes, territories that ensure the existence of each individual species, individual population, individual organism in infinitely diverse environmental conditions. Therefore, the movements of animals are so diverse and complex, so difficult to compare and classify. The classification of migrations is difficult not only because of their insufficient knowledge, but also because of the diversity of their manifestations in different groups of animals.

II. Types of animal movement

There are three types of animal movements: minor movements, migrations and migrations.

III. Origin of migrations

In general terms, science knows a lot, especially about the ways of animal migration. However, the causes of their occurrence and the orientation of animals during migration over long distances have not yet been sufficiently studied and are currently the subject of research by scientists from many countries.

For centuries, most of the theories that explain migration were based on the most bizarre guesses, often completely wrong. The strange, regularly repeated movements of animals have been of interest to people since the days when ancient hunters first began to follow herds that migrated across the vast savannahs of tropical Africa. On the rocks and walls of caves, such as Lasko, Altamira and Tassilin-Angier, masterpieces of ancient painting have preserved images of horses, bison and primitive bulls, which served our ancestors for thousands of years as a source of food and other means of subsistence.

In the 16th-18th centuries, a number of individuals believed that some animals, in order to avoid the adverse conditions of the coming cold weather, lay at the bottom of reservoirs and surfaced in the spring. Such a bizarre hypothesis was held by the Archbishop of Uppsala from Sweden, Olaf Magnus, Dr. Samuel Jones (1709-1784), the creator of the modern system of plants and animals, Carl Linnaeus (1707-1778), naturalist Lazzaro Spallanzani (1729-1799) and many others. Aristotle (384-322 BC) put forward a fantastic hypothesis of "transmutations", which explains the seasonal disappearance of some animal species and the simultaneous appearance of others. He even stated that animals were seen directly at the moment of transformation. This myth has survived to this day in some remote rural areas of England. But later, towards the end of the 18th century, the theories became more real, closer to true migrations. The vast majority of biologists, especially in the last century, when "explaining" seasonal transitions, referred to "innate instinct", "generic habit", usually without even putting any specific content into these concepts. Only later, with the development of IP Pavlov's teachings on conditioned and unconditioned reflexes, did they begin to attempt to formulate the concept of instinct more specifically, in a physiological sense. And, finally, by the end of the 19th century, the migration theory was recognized as proven.

Much less often, migration is driven by the desire to protect oneself from climatic extremes. Even on the islands of the Arctic Ocean, neither musk oxen nor bull-hunting wolves try to move to warmer places in winter. Arctic foxes even move further north at this time of the year to stay close to polar bears and feed on the remains of the seals they have killed. Lemmings and Scottish hare hares also remain to winter in the north, and besides them, other animals and birds. Even the baribal bear does not go south, except perhaps in the most severe winters, when he moves to places where you can safely hibernate without being subjected to such severe trials (if energy resources are overused, he risks not waking up after hibernation).

Migration ecology arose and is developing as a synthesis of ecology and physiology. This field of study of migration covers a wide range of different aspects of migratory behavior. It is very interesting to study the issues of the variability of migratory behavior, the difference in the timing and routes of migration, the individual variability of the migration distribution in time and across the territory in different species.

ANIMAL MIGRATION
regular movement of an animal population, during which individuals from one area of \u200b\u200bhabitat move to another, but then return back. Such circular travel may be seasonal, like the spring or autumn migration of birds, or it may take a lifetime to complete, as is seen in some Pacific salmon. Animal migrations have a pronounced adaptive (adaptive) character and arose in the course of evolution in a variety of species. Examples are the seasonal movements of microscopic animals from the deep part of lakes to shallow waters associated with changes in water temperature, or the migration of whales that swim from the polar regions to the subtropics in autumn, where their cubs are born, and return back to cold waters at the end of spring. It is practically impossible to find at least two species of animals migrating in exactly the same way. Some move singly, others only in groups. Some move at the same time very slowly, while others move very quickly and practically without stopping. For example, Arctic tern migrations are annual flights from areas close to North Pole(only a few degrees away from it), to areas where there are already antarctic ice. On the other hand, some frogs move only a few hundred meters during the year, separating the river from the nearest pond where they breed. In addition to migrations, animal populations can also demonstrate other types of movements. Some animals lead a nomadic lifestyle, and their movements are random in nature and are determined by the specific conditions prevailing in certain places. For example, many large herbivores that live in herds on the plains East Africa, move depending on the availability of food and climatic conditions in a particular area. These movements may take place along unsettled routes and are not associated with a mandatory return to the starting point. Another type of population movement is the so-called. "invasions" characteristic of some birds, mammals, as well as many insects. Invasions are usually observed in regions characterized by a harsh climate with sharp seasonal fluctuations. A well-known example is the brown lemming in the arctic tundra. During a 3-4-year cycle, the number of these animals increases, and after reaching a certain maximum, it quickly decreases. Upon reaching the peak of numbers, when the tundra is literally teeming with lemmings, they leave their native places en masse and go on a long journey. Very many fall prey to birds of prey and mammals, while most others die of disease and starvation, or drown in rivers and lakes or in the sea. However, some manage to survive a difficult time, and the population cycle begins again. The polar owl, also living in the Arctic regions, preys not only on lemmings, but also on hares. In those rare winters when there are few lemmings and hares, the snowy owl moves south in search of prey, sometimes even reaching California. Similar sudden invasions are sometimes observed in some seed-eating birds, usually staying in one area. For example, species living in the highlands or in northern latitudes, such as the Asian and North American nutcrackers, as well as the crossbill, in years of crop failure of conifer seeds - their main food - show disorderly movements from northern latitudes to more southern ones or from mountainous regions to valleys. Among insects, several species of locusts, found in Africa and Asia, have gained particular fame, and make mass flights when a very high population density is reached and there is a shortage of food. Moving to new areas, swarms of locusts can literally outshine the sun; only very few remain in the places where they were born. Unlike invasions, many other movements made by populations are hardly noticeable. They occur slowly and sometimes lead to a change in the distribution area of a particular species. Thus, over the past 30,000 years, man has migrated from Asia through the Bering Strait to North America, and then moved south as far as South America.
Food security. The farther from the equator certain land animals live, the more noticeable seasonal fluctuations in their food supply. In the tropics, the amount of food available, although varying with the alternation of dry and rainy periods, remains fairly constant throughout the year as a whole. As you move north or south, seasonal changes begin to appear. For example, in the tropics, insectivorous birds have a more or less constant amount of food at their disposal, while those nesting in Alaska or northern Canada are faced with the fact that there is a lot of food in late spring - early summer and very little in late summer - early autumn; as a result, migration to the south from places that were so favorable during the nesting period becomes absolutely necessary for survival. During the winter months in northern North America and Eurasia, lakes, rivers, and mud flats are ice-bound, serving as the main feeding grounds for many waterfowl and marsh birds in the summer. It is not surprising that the flight to the south is absolutely obligatory both for these birds and for the various raptors hunting them. Ecological analogs of insectivorous birds among mammals are small insectivorous bats, active (unlike birds) at night. In the northern latitudes, where it is cold in winter and there are no insects, many bats hibernate. Some species, such as the gray bat (Lasiurus cinereus) and its close relative- red leather (Lasiurus borealis), migrate south to warmer areas, where they remain active throughout the winter.
Reproduction. In many cases, the migration of animals is associated with the characteristics of reproduction. Some fish and marine mammals are examples. Different kinds Pacific salmon fish of the genus Oncorhynchus spawn in the rivers of the western coast of North America and the eastern coast of Asia. To spawning grounds, they sometimes have to climb up the rivers a thousand kilometers from the mouth. After spawning, adults die, and fry hatched from eggs grow and gradually slide into the sea. This journey can last from several weeks to many months, but only once in the sea, the fish begin to properly fatten and grow very quickly. Having reached sexual maturity, which takes from one to several years (depending on the type of fish), they return to the very rivers where they were born. There they breed and die, repeating the fate of their parents. Among marine mammals particularly impressive breeding migrations are demonstrated by gray whales. During summer months they stay in the Arctic Ocean and the Bering Sea, where at this time there is an abundance of small marine organisms (plankton) - their main food. In autumn, having accumulated a large amount of fat, the whales begin to migrate south to warmer areas. Moving along the Pacific coast of North America, most whales reach shallow lagoons off the western shores of the Gulf of California, where they give birth to cubs. In March, males, as well as females without cubs, begin to migrate northward, and after a few weeks, females with cubs follow them along the same route. At the beginning of summer, they all reach the cold waters of the Arctic and Subarctic. The purpose of the journey to the south undertaken by the whales is to keep their cubs in warm water during the first few weeks of life, until they have formed a layer of fat that can reliably protect from the cold in the northern seas. The migration of whales to the north is primarily a return to places rich in food.
Climate and day length. In the study of migration, it can be very difficult to separate the influence of climatic factors from those related to the supply of food or dictated by the characteristics of reproduction. The biological productivity that creates a food base for certain animals is itself largely determined by climate, and in areas far from the equator, the amount of food available often depends on temperature. For many organisms, the length of daylight is also very important, which regulates the normal reproduction cycle. The amount of light received per day, the so-called. photoperiod, often directly stimulates the start of migration. In many birds, for example, the activation of the sex glands, as well as migratory activity, directly depend on the spring increase in the length of daylight hours.
see also BIRDS .
Periodicity. In some animals, migrations correlate with the lunar cycle. One of the best-known examples is the grunion (Leuresthes tenuis), a small fish that lives off the coasts of California and northwestern Mexico. From early spring to early autumn, she spawns on sandbanks, and spawning occurs only during especially high (syzygy) tides observed in the first three to four nights after the full moon or new moon. During spawning, which lasts 1-3 hours, females are thrown ashore by waves, where they dig a hole with body movements, into which they lay eggs, which are immediately fertilized by males. The next surging wave carries the females back to the sea, and the juveniles hatch from the laid eggs already in the next spring tide.
Changes in the physiological state. Changes in the physiological state of individuals are very often associated with migrations. In addition to the close relationship observed in spring between an increase in sexual activity and the degree of readiness for migration, both in spring and autumn, immediately before migration, there is a rapid increase in fat reserves necessary for energy supply for long flights. Some birds replenish their energy reserves by stopping to feed during their flight, but others cover vast distances with little or no stop. For example, in the golden plover (Charadrius apricarius), the length of non-stop flight over water can reach 3200 km. The tiny red-throated hummingbird (Archilochus colubris), which lives in the eastern regions of North America in the summer, spends the winter in Central America(from Mexico to Panama). In the autumn, before migrating, these hummingbirds build up about two grams of fat - this is enough to cover more than 800 km of the path that runs over the waters of the Gulf of Mexico without stopping.
migratory routes. When migrating, each population follows the same route, which requires certain means of orientation. For a long time, the mechanisms of animal navigation seemed mysterious, but in the course of recent research, some questions have been clarified. The first step was to determine the routes of movement of animals; used for this various methods tagging (such as ringing birds). If a sufficiently large number of animals were marked and then found in other places, then it is possible not only to trace the route of migration, but also to find out how quickly it occurs and what is the participation of individuals of different sexes and different ages in it.
Orientation to the sun and stars. Vision is one of the main means by which migrating animals plot their route. In this case, some familiar features of the landscape can serve as landmarks, for example mountain ranges, rivers, lake shores or outlines of sea coasts. The ability to recognize the position of the stars at night and the position of the sun during the day may also play a certain role in orientation. The study of celestial orientation in animals began in the late 1940s with the work of the German ornithologist G. Kramer. Experimenting with migratory birds kept in captivity, he came to the conclusion that starlings, being diurnal migrants, are guided during their flights by the sun. A few years later, Franz and Eleanor Sauer were able to explain how birds that migrate at night find their way. Working with small passerines, they found that as long as the stars are not visible, the movements of birds are chaotic. Additional experiments carried out both in Europe and in America confirmed that many birds that are nocturnal migrants orient themselves by the stars during flight. The ability to navigate by the sun and stars is not unique to birds. Experiments with one of the species of toads (Bufo fowleri), living in the ponds of the central regions of the United States, have shown that young, until recently former tadpoles, individuals always move towards the shore. If toads of this age are placed in a circular cage, from which only its walls, the sky and the sun not covered by clouds are visible, then they always move in a direction perpendicular to the line of their native coast. Even if these toads are moved to some other place and placed in the same cages, their movement will again be oriented in the same direction. Similar experiments with frogs, namely the cricket tree frog, have shown that they can navigate both by the sun and by the stars. Orientation to the Sun was also found in white perch, a fish that lives in many freshwater lakes in North America. When the spawning period approaches, these fish from the open part of the lake move to the shore. If they are caught where they spawn and released in the same lake, but in the central part of it, they begin to move in the direction of the places where they were caught (this has been demonstrated using floats attached to their backs with thin nylon threads) .
Orientation with the help of smell. Orientation, based on the perception of smells, is extremely important for many organisms - from insects to mammals. An example of this is the monarch butterfly, which makes large seasonal movements. In autumn, males are the first to set off along a strictly defined route; odorous glands on their wings leave an odor trail, which is used for orientation by females flying behind them. Having reached the wintering grounds, the butterflies accumulate on the trees in huge numbers, and in the spring they set off on their way back to the north. Several species of Pacific salmon, returning from the sea to the very rivers where they were born, orient themselves with the help of the characteristic smell of the waters of their native river, imprinted in them from the first days after hatching from eggs. This odor is determined both by the minerals in the watershed and organic matter present in the waters of the river and giving it a chemical identity.
currents. Currents play an important role in the life of animals living in the seas, as well as in rivers (especially where visibility is limited). Amazing migrations associated with ocean currents are made by European and American eels (representatives of the genus Anguilla). Those that live in Europe grow and mature in the rivers flowing into the Atlantic Ocean - from Scandinavia to the Iberian Peninsula. After spending 5 to 20 years there and reaching sexual maturity, they roll into the sea, then, drifting with the Canary and North Equatorial currents, cross the Atlantic Ocean and reach the Sargasso Sea - a specific area in the northwestern part of the Atlantic, where there are no currents and in abundance large algae floating near the surface develop. In these places, at great depths, eels multiply, after which they die. The hatched larvae rise to the surface and are transported with the waters of the Gulf Stream to the shores of Europe. This journey takes them three years, and by the end of it, the eels are already able to move up the river systems, where they remain until puberty. Similar migrations are made by American eels living in the rivers of the Atlantic coast.
Impending dangers. Migration always requires the consumption of stored energy, and the amount of energy needed to cover long distances must be simply enormous. Therefore, migratory animals are always in danger of physical exhaustion. In addition, they easily fall prey to predators. Successful overcoming of the migration route to a very large extent also depends on climatic factors. The sudden onset of a cold front during the northward migration of birds in spring can have fatal consequences for many birds, and fogs and storms cause them to lose their bearings and go astray. A serious danger for many migrants is a person. Knowing the routes of commercial animal species, people hunt them for food or for other purposes, including purely sporting ones. Various structures, such as television towers and skyscrapers, also cause the death of hundreds of thousands of birds. The blocking of rivers by dams creates obstacles for the rise of fish upstream to spawning grounds.
See also BIOLOGICAL RHYTHMS.
LITERATURE
Cloudsley-Thompson D. Animal migrations. M., 1982

Collier Encyclopedia. - Open Society. 2000 .

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