Migrations of animals: examples, causes, types. Why do animals make migrations?

Do you know why animals are migrating? Grade 7 learns about this in biology lessons. And already then, during the acquaintance with the secrets of biological science, the consciousness of children begins to accustom to the understanding of the ordinary fact: people migrate, animals migrate. And if you understand well, the reasons for all the same.

Migratory animals (Latin migratio) - regular movement of a group of animals with a change in the main habitat along a certain route. The most common are similar phenomena in birds (we all observe the migration of storks, geese, ducks, starlings and other birds in the autumn) and fish. Movements of animals are less studied. This is due to the fact that they lead mostly a secretive way of life, it is often impossible to follow them.

Migrations have a pronounced adaptive character, this feature of representatives of the animal world is observed in a variety of species and has emerged in the process of evolution.

Seasonal migrations are more characteristic of birds, inhabitants of temperate latitudes. Also they are inherent in some mammals: wildebeest, reindeer, some species of bats, fish (sturgeon, European eel), reptiles (sea turtle), crustaceans (lobster), insects (butterfly monarch) are changing the habitat of the antelope.

Why do animals make migrations?

The most important reason for animal movements is a change in habitat conditions, most often for the worse. For example, reindeer move with the onset of winter from the tundra to the forest tundra due to the lack of food and the difficulty of its extraction in the area covered by snow. And seasonal migration of microscopic animals to shallow water from the deepest parts of lakes is associated with a change in the temperature of the water.

No less important motivation is reproduction, when an animal needs a different environment for procreation. Another reason for migration is associated with natural disasters. Each of the reasons we will try to consider in this article for an example.

Types of animal migration

Conventionally, we can distinguish two types of migration - active and passive. In active migration of animals, several subspecies are distinguished: displacements are seasonal (diurnal), periodic (horizontal and vertical), and age. Let's try to understand what each species is.

So, seasonal (daily) migration of animals. Examples of such movements are best considered on fish and birds. To date, about 8,500 species of birds are known to science, most of which lead a sedentary life, although they are susceptible to migration within the range of their nesting time. Seasonal movements of birds on wintering are more common in Arctic inhabitants and temperate latitudes: with the approach of the winter period birds fly to a softer, warm climate.

An interesting fact: the larger the bird, the longer it moves, the smallest migratory birds can remain in the air continuously for up to 90 hours, crossing the route up to 4000 km.

Fish migrate vertically: during the rain they are almost on the surface, in the heat or in the winter - they tend to the depths of water bodies. But only two fish change habitual habitat - it's salmon and European eel. Surprisingly, but the fact: the change of reservoirs with salt and fresh water occurs in these fish two times in life - at the time of birth and during the breeding season, however, this applies only to females that die after laying eggs.

Interestingly, at the time of salmon spawning, brown bears migrate too, leaving forests, settling on rivers that swarm with salmon. Thus, it turns out that they follow their fodder base.

As noted earlier, the periodic migration of animals can be divided into two subspecies: horizontal and vertical. Let us consider these phenomena in more detail.

Horizontal migration of animals is associated with the movement of individuals in the search for food. So, for example, the gray whale moves to the summer from the North Ocean to the Atlantic (subtropical, tropical part), where at that time it is full of plankton - the main food of the whale.

Vertical migrations are characteristic of high-mountain animals, which in winter descend into the forest belt, and in summer, as the snow melts and the grasses burn out in the lowland, they climb back up the mountain.

There is still such a thing as the age-related migration of animals. Similar movements are revealed better on the example of large predators. Thus, a tiger, in its essence, is a solitary animal with its own vast territory, which it leaves only during the rut. The newly born cubs live with the female before reaching the sexual maturity (usually 3-4 years), after which the males are separated and leave the family in search of their own territory.

Reasons and examples of migration

We have already talked about what is connected with such a phenomenon as the migration of animals. Examples on specific representatives will be considered further.

We will begin our acquaintance with fish, since only two of their species are subject to displacement. These include salmon and European eel. There are other few species of animals that make migrations, but we'll talk about them later. So why do fish migrate? What is the reason?

Change of fish habitat

Anadromous fish are a species that lives in a certain habitat, but at the time of reproduction it radically changes it. What is the reason for this?

Salmon (lat. Salmo salar) is born in fresh water, then with river flows quickly moves to the sea-ocean where lives 5-7 years in anticipation of puberty. And now the long-awaited moment has come - the individuals have grown and are ready to leave offspring. Only here is the ill luck - the salty water they like, but the kids refuse to appear in it. The fish "remembers" that they were born in fresh water, which means that it needs to change the salty seas-oceans to rivers, and even better - to the mountain. There the most favorable conditions for reproduction. Only not all parents will achieve the desired goal - there is a predator sitting there, deftly catching a fish from the mountain stream, ripping off the belly and eating only caviar. Only a brown bear can do this, which is tied to the migration of animals - the source of the food base.

The European eel (Latin Anguilla anguilla) is the exact opposite of salmon. The eel is born in the salt water of the Sargasso Sea, it occurs at a depth of up to 400 m. The female produces about half a million eggs, which turn into a larva, similar to a willow leaf. Larvae for their cardinal difference from their parents were given a separate name - leptotsefal. With the example of these fish, we can look in detail at the form of passive migration: the larvae float to the surface, the Gulf Stream is picked up by them, and for three years they are moving in warm water to the coast of the European part of Eurasia. By this time, the leptotsefal takes on the shape of an eel, only a small one - about 6 cm. At this moment, the eel moves to the mouth of the river, rising upstream, the fish turns into an adult. So passes 9, and maybe 12 years (no more), acne becomes sexually mature, sex differences in coloring sharply appear. It's time to spawn - back to the ocean.

Migrations of mammals

The gray whale (from the Latin Eschrichtius robustus) dwells in the Arctic Ocean, but, paradoxically, females and males begin to move south along the coast from October. By December-January, the pair have reached the Gulf of California, where matings and maternity begin in warm waters, after which the males return north, while pregnant females and individuals with the cubs return home only in March-April.

Pregnancy in whales lasts about a year, so in warm waters either conceive, or bring to light a new offspring. For young animals, it is very important - in the first 2-3 weeks of life, children in warm waters gain a fatty layer that allows them to return to the severe Arctic Ocean.

On the example of moose, we can explain such a concept as the ways of migration of animals. Elk, in the common people "sukhaty" (from Latin Alces alces), is distributed in the forest zone of the Northern Hemisphere. As soon as the first snow appears, the rivers become covered with ice, the moose starts moving to the southern regions, where grasses are preserved, the ponds do not freeze. Interestingly, when migrating from October to January, moose walk along the trampled path: the first follow the females with the young, the males follow them. On the way back, the animals return the same way, only now the males go ahead, clearing the path from the overgrown greenery. With the approach to the habitat, the groups wander off - single females in one direction, females with cubs - in another, males - in the third.

Tigers (Latin Panthera tigris), the largest representatives of felines, lead a solitary life: for a female it takes up to 50 km² of personal territory, for a male - up to 100 km². The meeting occurs during the breeding season, most often the female itself attracts the male, leaving various marks. Having fertilized the tigress, the male returns to his territory or to search for the next female.

Here we see an example of migration of animals within the range, but with violation of territorial boundaries. The new offspring live with the mother until the "kids" learn to hunt, which takes quite a long time. So, the cubs are with a tigress before puberty, after which already grown up individuals go to conquer new territories. Examples of age migration can be added to the previously described European eel.

Mass migrations of animals are inherent in many species, but the movement of bats is an indescribable sight. In general, bats are prone to sedentary life, but if the animals live in a temperate zone, then they are forced to go to the south for wintering. If the temperature of the air in the winter period is kept within 0 ºС, then bats can overwinter in the attics of buildings. At this time, the mice fall into a winter sleep. In forced migration, the bats are guided by instincts and move along those routes that are used from generation to generation.

Remember the vertical migration and pay attention to the inhabitants of the mountains. In the mountains, at an altitude of thousands of meters, an extraordinary zoological diversity: chinchillas, snow leopards, pumas, goats, sheep, yaks, archawn oak, white eared pheasant, kea. For all residents of the highlands are characterized by thick wool and plumage, which prevent hypothermia of animals. Some animals in winter in burrows fall into a hibernation, and birds in the crevices of rocks make nests and warm themselves in groups. But representatives of ungulates descend to the foot of the rocks in search of food, followed by predators pursuing their prey.

An interesting fact: mountain goats and sheep are able to migrate through the rocks without stepping on the mountain paths. And all thanks to the special structure of the hooves: the soft pads are quickly restored, the hooves have the ability to expand widely, which is important when traveling through a rocky terrain.

Reasons for changing the habitat of birds

Migratory birds are observed both in the Northern and Southern Hemisphere. The more sharply the climate changes, the more pronounced the flights. Thus, the crows and turtledoves that we habitually become migratory if they live in the northern regions, where severe, snowy winters deprive birds of the possibility of harvesting food. Inhabitants of the southern part of Europe lead a sedentary lifestyle due to the absence of sudden temperature changes. Interesting behavior of birds in Africa: here you can simultaneously observe movements from north to south, and from south to north. The reason for such migrations is hidden in the preference for a humid or arid climate.

Birds can make quite a long flight. For example, the habitat of the white stork (Latin Ciconia ciconia) is in Europe, and the bird in the winter in Africa, twice a year overcoming the distance of 10-15 thousand km. But the most unique among migratory birds is the polar tern (Latin Sterna paradisaea). Krachka nests in the tundra, here it also displays chicks. With the onset of autumn, it migrates to the Southern Hemisphere, and in the spring it returns. So, twice a year this bird overcomes up to 17 thousand km. It is interesting that in spring and autumn the tern flew different routes.

Movements of reptiles

We will analyze on an example of a sea turtle (Latin Cheloniidae), in what the reason of mass migrations of animals. Sea turtles multiply only in certain places. Thus, the Atlantic Atlantis (Latin Lepidochelys kempii) reproduces on a single island in Mexico, where in 1947 scientists recorded about 42 thousand females that arrived for laying eggs.

Thanks to the olive sea turtle (Latin Lepidochelys olivacea), the term "arribide" appeared in science. The phenomenon is that thousands of olive grouses are collected for mating in one day, after which, selecting the island, the females practically simultaneously make clutches of millions of eggs.

Why do crustaceans migrate?

Lobster (Latin Achelata) also moves at a specific time. The causes of migration of animals of this species are still not explained by science. In autumn, the lobsters gather in a column of thousands of individuals and make a march-throw from the island of Bimini to the Great Bahamian Bank. So far, there is only one possible explanation for this behavior: the light day begins to decline in autumn, which causes the lobsters to change their habitat.

The spiny lobster (Latin Panulirus argus) is also considered a nomadic representative of crustaceans. At the beginning of winter, it goes into deeper waters. Scientists for a long time believed that the reason for moving the lobster - reproduction, but later it was found that the laying of eggs occurs much later than the migration, only a few months. Scientists call different reasons for changing the habitat of lobsters. Some, for example, believe that the migration of these crustaceans is a relic of the glacial period, when in the winter they changed the cold waters to warmer deep ones.

Migrating lobster is a truly amazing sight! Several hundred individuals move columns one after another. What is most interesting, lobsters keep constant contact with each other. So, the one who is behind, keeps his antennas on the armor of the one who goes ahead.

Examples of migrations of insects

Butterfly danaid-monarch (Latin Danaus plexippus) - the most famous inhabitant of North America. During the migration of animals, it is noticed on the territory of Ukraine, Russia, the Azores, North Africa. In Mexico, the state of Michoacan, even there is a reserve of a butterfly-monarch.

In the issue of migration, this insect also distinguished itself: the Danaide is one of the few representatives of its class that can cross the Atlantic Ocean. Already in August the monarchs begin to migrate to the southern territories. The life span of this butterfly is about two months, so the migration of animals takes place for generations.

Diabase is the reproductive phase into which the Danada, born at the end of summer, enters, which allows the butterfly to live for about 7 months and reach the wintering site. The monarch butterfly has an amazing "solar sensor" that allows the third, fourth generations to return to the wintering grounds of their ancestors. Interestingly, the most favorable climate for these butterflies was found in Bermuda, where some insects remain year-round.

European species also migrate. The wildflowers, for example, hibernate and reproduce in North Africa, and their offspring are already moving north and there is a summer generation, after which it again flies to Africa. In the spring, history repeats itself.

What is interesting is that the thistles fly by groups and can cover a distance of 500 km in one day. In total, during migration they can fly as much as 5000 km! And the speed of their flight is rather big - it is 25-30 km / hour.

Some butterflies do not migrate constantly, but only depending on the conditions. These include urticaria, mahaone, tramadress, cabbage, admiral. All these species live in Northern and Central Europe, but can move south under adverse circumstances.

But an oleander brazier, for example, annually moves from Turkey and North Africa to Eastern and Central Europe. There these butterflies multiply, but, unfortunately, in winter most of their offspring die. In the spring, the next generation migrates from the south.

A small conclusion and conclusions

Here we are a little and figured out why animals make migrations. Indeed, the reasons are diverse, but I want to note the two most common. We all remember the story of Mowgli, especially the moment when the jungle came a period of drought. All animals were drawn to a single stream, where parity was to be observed: all are equal, hunting is taboo. Such migration occurs, as a rule, within the habitat range, when animals (more often inhabitants of steppes, semi-deserts, deserts) migrate in the drought period in search of food and water from place to place, most often these are ungulates. However, the movement of herds, herds entails the movement of some predators (hyenas, griffins), which need to be located near the food base. Thus, food and water cause large groups of animals of several species to migrate.

An important reason is reproduction. Active migration of animals during the breeding season, in particular sea turtles, is impressive and fascinating.

Many species of animals migrate: some within the range, others overcome thousands of kilometers to reach a favorable climate; The third cardinally change the habitat (remember about sturgeon and European eel).

Yes, the migration of different animals has a different nature, different reasons, but it unites all one - the thirst for life.