Do you know why animals migrate? Grade 7 learns about this in biology lessons. And even then, during the acquaintance with the secrets of biological science, the minds of children begin to be accustomed to understanding the everyday fact: people migrate, animals migrate. And if you understand it well, everyone has the same reasons.
Animal migration (lat. migratio) is the regular movement of a group of animals with a change in the main habitat along a certain route. Such phenomena are most common in birds (we all observe the migration of storks, geese, ducks, starlings and other birds in autumn) and fish. Movements of animals have been studied less. This is due to the fact that they lead a mostly secretive lifestyle, it is often impossible to track them.
Migrations have a pronounced adaptive character, this feature of representatives of the animal world is observed in a variety of species and arose in the process of evolution.
Seasonal migrations are more typical for birds living in temperate latitudes. Also theyinherent in some mammals: wildebeest, reindeer, some varieties of bats, fish (sturgeon, European eel), reptiles (sea turtle), crustaceans (lobster), insects (monarch butterfly) change their habitat.
Why do animals migrate?
The most important reason for animal movements is a change in living conditions, most often for the worse. For example, reindeer move from the tundra to the forest-tundra with the onset of winter due to the lack of food and the difficulty of obtaining it in areas covered with snow. And seasonal migrations of microscopic animals to shallow waters from the deep parts of lakes are associated with changes in water temperature.
An equally important motivation is reproduction, when an animal needs a different environment for procreation. Another reason for migration is related to natural disasters. We will try to consider each of the reasons in this article using an example.
Types of animal migration
Two types of migration can be conventionally distinguished – active and passive. In the active migration of animals, several subspecies are distinguished: movements are seasonal (daily), periodic (horizontal and vertical), and age. Let's try to figure out what each variety is.
So, seasonal (daily) migration of animals. Examples of such movements are best seen in fish and birds. To date, about 8,500 species of birds are known to science, most of which lead a sedentary lifestyle, although they are subject to migration within their habitat for the duration of nesting. Seasonalmovements of birds for wintering are more characteristic of the inhabitants of the Arctic and temperate latitudes: with the approach of the winter period, birds fly to a milder, warmer climate.
Interesting fact: the larger the bird, the longer distances it travels, while the smallest migrating birds can stay in the air continuously for up to 90 hours, covering the route up to 4000 km.
Fishes migrate vertically: during rain they are practically on the surface, in heat or winter they tend to the depths of water bodies. But only two fish change their habitual habitat - salmon and European eel. Surprisingly, it is a fact: these fish change reservoirs with s alt and fresh water twice in their lives - at the time of birth and during the breeding season, however, this only applies to females that die after laying eggs.
Interestingly, at the time of salmon spawning, brown bears also migrate, leaving the forests, settling on rivers teeming with salmon. Thus, it turns out that they follow their food supply.
As noted earlier, periodic animal migrations can be divided into two subspecies: horizontal and vertical. Let's take a closer look at these phenomena.
Horizontal migrations of animals are associated with the movement of individuals in search of food. So, for example, by summer, a gray whale moves from the North Ocean to the Atlantic (subtropical, tropical part), where at this time there is a lot of plankton - the whale's main food.
Vertical migrations are inherent in alpine animals, which in winterdescend into the forest belt, and in the summer, as the snow melts and the grasses in the lowlands burn out, they rise back to the mountain.
There is also such a thing as age-related migration of animals. Similar movements are revealed better on the example of large predators. So, the tiger, in its essence, is a solitary animal with its own huge territory, which it leaves only during the rutting season. The cubs that are born live with the female until they reach sexual maturity (usually 3-4 years), after which the males separate and leave the family in search of their own territory.
Reasons and examples of migration
We have already talked about what the phenomenon of animal migration is connected with. We will consider examples on specific representatives below.
Let's start with fish, since only two of their species are subject to movement. These include salmon and European eel. There are other few species of animals that make migrations, but we will talk about them later. So why do fish migrate? What causes it?
Change of fish habitat
Anadromous fish is a species that lives in a certain habitat, but changes it drastically during the breeding season. What is it about?
Salmon (lat. Salmo salar) is born in fresh water, then with river flows quickly moves to the sea-ocean, where it lives for 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 bad luck - they like s alt water, but the kids refuseappear in it. The fish “remembers” that it was born in fresh water, which means that it needs to change the s alty seas-oceans to rivers, and even better, to mountain ones. There are the most favorable conditions for reproduction. Only not all parents will achieve the desired goal - a predator sits here, which deftly catches a fish from a mountain stream, ripping open its belly and eating only caviar. Only a brown bear is capable of this, which is tied to animal migration - a source of food supply.
European eel (lat. Anguilla anguilla) is the exact opposite of salmon. The eel is born in the s alty water of the Sargasso Sea, it happens at a depth of up to 400 m. The female produces about half a million eggs, which turn into a larva that looks like a willow leaf. For their fundamental difference from their parents, the larvae received a separate name - leptocephalus. On the example of these fish, we can consider in detail the type of passive migration: the larvae float to the surface, they are picked up by the Gulf Stream, and so for three years they move in warm water to the coast of the European part of Eurasia. By this time, the leptocephalus takes on the shape of an eel, only reduced - about 6 cm. At this moment, the eel moves to the mouths of the rivers, rising upstream, the fish turns into an adult. So 9 or maybe 12 years pass (no more), acne becomes sexually mature, sexual differences in color appear sharply. Time to spawn - back to the ocean.
Mammal migrations
The gray whale (from lat. Eschrichtius robustus) lives in the Arctic Ocean, but, paradoxically, females andmales from October begin to move south along the coast. By December-January, couples reach the Gulf of California, where they start mating and giving birth in warm waters, after which males return north, and pregnant females and individuals with cubs return home only in March-April.
Pregnancy in whales lasts about a year, so in warm waters they either conceive or bring new offspring into the world. For young animals, this is very important - in the first 2-3 weeks of life, babies in warm waters gain fat, which allows them to return to the harsh Arctic Ocean.
On the example of moose, we can explain such a concept as the ways of animal migration. Elk, in the common people "elk" (from lat. Alces alces), is common in the forest zone of the Northern Hemisphere. As soon as the first snow appears, the rivers are covered with ice, the elk begins to move to the southern regions, where grass growth is preserved, and water bodies do not freeze. It is interesting that, migrating from October to January, moose follow a trodden path: females with young animals follow first, followed by males. On the way back, the animals return by the same road, only now the males go ahead, clearing the path from overgrown greenery. As they approach the habitat, the groups disperse - single females in one direction, females with cubs in the other, males in the third.
Tigers (lat. Panthera tigris), the largest representatives of cats, lead a solitary lifestyle: a female requires 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 herself attracts the male,leaving different marks. Having fertilized the tigress, the male returns to his territory or in search of the next female.
Here we see an example of animal migration within the habitat, but with violation of territorial boundaries. The new offspring lives with their mother until the "kids" learn to hunt, which takes quite a long time. So, the cubs are with the tigress until puberty, after which the already grown individuals go to conquer new territories. The previously described European eel can be added to examples of age migration.
Mass migrations of animals are inherent in many species, but the movement of bats is an indescribable sight. In general, bats are prone to a sedentary lifestyle, but if the animals live in the temperate zone, then they are forced to go south for wintering. If the air temperature in winter is kept within 0 ºС, then bats can overwinter in the attics of buildings. At this time, the mice fall into winter sleep. During forced migration, bats are guided by instincts and move along those routes that are used from generation to generation.
Let's think about vertical migration and pay attention to the inhabitants of the mountains. In the mountains, at an altitude of thousands of meters, there is an extraordinary zoodiversity: chinchillas, snow leopards, cougars, goats, rams, yaks, juniper grosbeak, white-eared pheasant, kea. All inhabitants of the highlands are characterized by thick wool and plumage, which prevent hypothermia of animals. Some animals hibernate in their burrows in winter, while birdscrevices of rocks make nests and bask in groups. But representatives of ungulates descend to the foot of the rocks in search of food, followed by predators chasing their prey.
Interesting fact: mountain goats and sheep are able to migrate over rocks without stepping on mountain paths. And all thanks to the special structure of the hooves: soft pads are quickly restored, the hooves have the ability to move apart widely, which is important when moving on rocky terrain.
Reasons for changing bird habitats
Migratory birds are observed in both the Northern and Southern Hemispheres. The sharper the climate changes, the more pronounced the flights. Thus, the crows and turtledoves familiar to us become migratory if they live in the northern regions, where harsh, snowy winters deprive birds of the opportunity to obtain food. The inhabitants of the southern part of Europe lead a sedentary lifestyle due to the absence of sudden changes in temperature. The behavior of birds in Africa is interesting: here one can simultaneously observe movements both 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 fairly long flights. For example, the habitat of the white stork (lat. Ciconia ciconia) is in Europe, and the bird winters in Africa, covering a distance of 10-15 thousand km 2 times a year. But the most unique among migratory birds is the arctic tern (lat. Sterna paradisaea). The tern nests in the tundra and breeds chicks here. With the onset of autumn, she migrates to the Southern Hemisphere, and returns in the spring. So, twice a year this birdovercomes up to 17 thousand km. Interestingly, in spring and autumn, the tern flies by different routes.
Movement of reptiles
Let's look at the example of a sea turtle (lat. Cheloniidae), what is the reason for the mass migrations of animals. Sea turtles only breed in certain places. Thus, the Atlantic Ridley (lat. Lepidochelys kempii) breeds on a single island in Mexico, where in 1947 scientists recorded approximately 42 thousand females that sailed to lay eggs.
Thanks to the olive sea turtle (lat. Lepidochelys olivacea), the term "arribida" appeared in science. The phenomenon is that thousands of olive ridleys gather for mating in one day, after which, having chosen an island, the females lay millions of eggs almost simultaneously.
Why crustaceans migrate
Lobster (lat. Achelata) also moves at a certain time. Science still does not explain the reasons for the migration of animals of this species. In autumn, lobsters gather in a column of thousands of individuals and make a forced march from Bimini Island to the Grand Bahama Bank. So far, there is only one hypothetical explanation for this behavior: in the fall, daylight hours begin to decrease, which forces the lobsters to change their habitat.
Prickly lobster (lat. Panulirus argus) is also considered a nomadic representative of crustaceans. At the beginning of winter, it moves to deeper waters. Scientists have long believed that the reason for the movement of the lobster is reproduction, but later it was found out that the masonryeggs occurs much later than migration, only after a few months. Scientists name different reasons for changing the habitat of spiny lobsters. Some, for example, believe that the migration of these crustaceans is a relic of the ice age, when in winter they changed cold waters for warmer deep ones.
Migration of lobsters is truly an amazing sight! Several hundred individuals move in columns one after another. What is most interesting, lobsters maintain constant contact with each other. So, the one in the back keeps his antennae on the shell of the one in front.
Examples of insect migrations
The monarch butterfly (lat. Danaus plexippus) is the most famous inhabitant of North America. During periods of animal migration, it is noticed on the territory of Ukraine, Russia, the Azores, North Africa. There is even a Monarch Butterfly Sanctuary in Michoacán, Mexico.
In the issue of migration, this insect also distinguished itself: the danaid 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 lifespan of this butterfly is about two months, so the migration of animals occurs in generations.
Diabase is the reproductive phase, which enters the danaid, born at the end of summer, which allows the butterfly to live for about 7 more months and reach the wintering place. The monarch butterfly has an amazing "solar sensor" that allows the third and fourth generations to return to the wintering places of their ancestors. Interestingly, the most favorable climate for these butterfliesended up in Bermuda, where some insects stay all year round.
European species also migrate. Thistles, for example, winter and breed in North Africa, and already their offspring move to the north and there they hatch the summer generation, after which they fly back to Africa. In the spring, history repeats itself.
Interestingly, thistles fly in groups and can cover a distance of 500 km in one day. In total, during the migration they can fly as much as 5000 km! And their flight speed is rather big - it is 25-30 km/h.
Some butterflies do not migrate constantly, but only depending on the conditions. These include urticaria, swallowtail, mourning, cabbage, admiral. All of these species are found in Northern and Central Europe, but may move south under adverse circumstances.
But the oleander hawk moth, for example, annually moves from Turkey and North Africa to Eastern and Central Europe. There, these butterflies breed, but, unfortunately, in winter, most of their offspring die. In the spring, the next generation migrates from the south.
Small conclusion and conclusions
Here we are a little and figured out why animals migrate. Indeed, the reasons are varied, but I want to note the two most common. We all remember the story of Mowgli, especially the moment when a period of drought began in the jungle. All the animals reached for the only river where parity was to be observed: everyone is equal, hunting is a taboo. This migration usually occurs inwithin the habitat, when animals (more often inhabitants of the steppes, semi-deserts, deserts) migrate in search of food and water from place to place during the drought, most often these are representatives of ungulates. However, the movement of herds, herds also entails the movement of some predators (hyenas, vultures), which need to be close to the food supply. Thus, food and water cause large groups of animals of several species to migrate.
An important reason is reproduction. The active migration of animals during the breeding season, in particular, sea turtles, is impressive and fascinating.
Many species of animals move: some within their habitat, others travel thousands of kilometers to reach a favorable climate; others radically change their habitat (remember the sturgeon and the European eel).
Yes, the migration of different animals has a different nature, different reasons, but they all have one thing in common - the thirst for life.
