Do you know why animal migration occurs? Grade 7 learns about this in biology classes. And even then, during an acquaintance with the secrets of biological science, the children’s consciousness begins to be accustomed to understanding the ordinary fact: people migrate, animals migrate. And if you understand it well, everyone has the same reasons.
Animal migration (lat. Migratio) - regular movement of a group of animals with a change in the main habitat along a specific route. The most common such phenomena in birds (we all see the autumn migration of storks, geese, ducks, starlings and other birds) and fish. The movements of animals are less studied. This is due to the fact that they lead mainly a secretive lifestyle, it is often impossible to follow them.
Migrations have a pronounced adaptive nature, this feature of representatives of the animal world is observed in various species and arose in the process of evolution.
Seasonal migrations are more characteristic of birds, inhabitants of temperate latitudes. They are also characteristic of some mammals: they change the habitat of wildebeest, reindeer, some species of bats, fish (sturgeon, European eel), reptiles (sea turtle), crustaceans (spiny lobster), insects (monarch butterfly).
Why do animals migrate?
The main reason for animal movements is a change in living 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 production in the area covered with snow. And seasonal migrations of microscopic animals into shallow water from the deep parts of lakes are associated with changes in water temperature.
An equally important motivation is reproduction, when the animal needs a different environment for procreation. Another reason for migration is associated with natural disasters. We will try to consider each of the reasons in this article using an example.
Types of animal migration
Conventionally, two types of migration can be distinguished - active and passive. In active migration of animals, several subspecies are distinguished: movements are seasonal (diurnal), periodic (horizontal and vertical), and age-related. 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. Today, science knows about 8500 species of birds, most of which lead a sedentary lifestyle, although they are subject to migrations within their habitat at the time of nesting. Seasonal migrations 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 into a milder, warmer climate.
An interesting fact: the larger the bird, the longer it moves, the smallest of the migratory birds can remain in the air continuously for up to 90 hours, covering the route up to 4000 km.
Fish migrate vertically: during rain they are almost on the surface, in heat or in winter - they tend to the depths of water bodies. But only two fish change their habitat - this is salmon and European eel. Surprisingly, the fact is: the change of water bodies with salt and fresh water occurs in these fish twice in their 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 also migrate, leaving the forest, settling on the rivers teeming with salmon. Thus, it turns out that they are following their food supply.
As noted earlier, periodic animal migrations can be divided into two subspecies: horizontal and vertical. Let us consider these phenomena in more detail.
Horizontal animal migrations are associated with the movement of individuals in search of food. So, for example, gray whale moves from the North Ocean to the Atlantic (subtropical, tropical part) by summer, where at this time it is full of plankton - the main food of the whale.
Vertical migrations are inherent in alpine animals, which descend into the forest belt in winter, and in summer, as the snow converges and grass burns out in the lowland, they climb back up the mountain.
There is also such a thing as age-related migration of animals. Such movements are better revealed by the example of large predators. So, the tiger, in essence, is a solitary animal with its own vast territory, which he leaves only during the rutting season. The cubs that were born live with the female until they reach puberty (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 is associated with the phenomenon of animal migration. Examples on specific representatives will be considered later.
Let's start our acquaintance 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 is the reason?
Change of habitat for fish
Anadromous fish - a species that lives in a specific habitat, but at the time of reproduction dramatically changes it. What is the reason for this?
Salmon (Latin Salmo salar) is born in fresh water, then quickly moves with river flows to the sea-ocean, where it lives 5-7 years in anticipation of puberty. And now the long-awaited moment has come - individuals have grown and are ready to leave offspring. Only here is the bad luck - they like salt water, but the kids refuse to appear in it. The fish "remembers" that it was born in fresh water, which means that it needs to change the salty sea-oceans to rivers, and even better - to mountains. There are the most favorable conditions for reproduction. Only not all parents will achieve the desired goal - a predator sits here, who cleverly catches fish from a mountain stream, ripping open his belly and eating only caviar. Only a brown bear is capable of this, which is tied to the migration of animals - the source of the food supply.
European eel (lat.Anguilla anguilla) - the exact opposite of salmon. 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 pass into a larva similar to a willow leaf. Larvae for their cardinal difference from their parents received a separate name - leptocephalus. Using 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 travel 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 point, the eel moves to the mouths of the rivers, rising upstream, the fish turns into an adult. So goes 9, or maybe 12 years (no more), blackheads become sexually mature, gender differences in color sharply appear. It's time to spawn - back to the ocean.
Mammal Migration
A gray whale (from the Latin Eschrichtius robustus) lives in the Arctic Ocean, but, paradoxically, in October, females and males 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 the males return to the 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 give birth to new offspring. For young animals, this is very important - in the first 2-3 weeks of life, babies in the warm waters gain fat, which allows them to return to the harsh Arctic Ocean.
Using the example of moose, we can explain such a thing as animal migration routes. 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 are covered with ice, the elk begins to move to the southern areas, where grass is preserved, the ponds do not freeze. Interestingly, migrating from October to January, moose follow a trodden path: females with young growth are the first to follow, males follow them. On the way back, animals return on the same road, only now the males go ahead, clearing the path from overgrown greenery. With approaching the habitat, the groups disperse - lonely females in one direction, females with cubs - in the other, males - in the third.
Tigers (Latin Panthera tigris), the largest representatives of cats, lead a solitary lifestyle: for a female, up to 50 km² of personal territory is required, for a male, up to 100 km². The meeting occurs during the breeding season, most often the female herself attracts the male, leaving various 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. New offspring live with their mother until the “babies” 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. Examples of age-related migration include the previously described European eel.
Massive migrations of animals are inherent in many species, but the movement of bats is an indescribable sight. In general, bats are prone to a settled lifestyle, but if the animals live in the temperate zone, then they are forced to go south for the winter. If the air temperature in the winter is kept within 0 º, then bats can overwinter in the attics of buildings. At this time, the mice fall into winter sleep. In forced migration, bats are guided by instincts and move along the routes that are used from generation to generation.
Recall the vertical migration and pay attention to the inhabitants of the mountains. In the mountains, at an altitude of thousands of meters, there is an unusual zoological diversity: chinchillas, snow leopards, cougars, goats, rams, yaks, juniper oak tree, white-eared pheasant, kea. All inhabitants of the highlands are characterized by dense hair and plumage, which prevent overcooling of animals. Some animals hibernate in burrows in the winter, and birds in the crevices of rocks make nests and bask in groups. But the representatives of ungulates descend to the foot of the rocks in search of food, followed by predators chasing their prey.
An interesting fact: mountain goats and sheep are able to migrate along the rocks without stepping on mountain trails. And all thanks to the special structure of the hooves: soft pads are quickly restored, the hooves have the ability to widely move apart, which is important when traveling on rocky terrain.
Reasons for changing bird habitat
Migratory birds are observed in both the Northern and Southern Hemispheres. The sharper the climate changes, the more pronounced the flights are. Thus, crows and Streptopelia habitual to us become migratory if they live in northern regions, where severe, snowy winters deprive birds of the opportunity to get food. The inhabitants of southern Europe lead a sedentary lifestyle due to the absence of sudden changes in temperature. The behavior of birds in Africa is interesting: here you 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 rather long flights. For example, the habitat of the white stork (Latin Ciconia ciconia) is in Europe, and the bird overwinters in Africa, 2 times a year covering a distance of 10-15 thousand km. But the most unique among migratory birds is the polar tern (lat. Sterna paradisaea). Krachka nests in the tundra, it also displays chicks. With the onset of autumn, she migrates to the Southern Hemisphere, and returns in the spring. So, twice a year this bird overcomes up to 17 thousand km. Interestingly, in spring and autumn the tern flies different routes.
Reptile movements
Let us examine the example of a sea turtle (lat. Cheloniidae), what is the reason for the mass migration of animals. Sea turtles breed only in certain places. So, the Atlantic Ridley (Latin: Lepidochelys kempii) breeds on the only island in Mexico, where in 1947, scientists registered about 42 thousand females who 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 riddles gather in one day for mating, after which, choosing an island, the females make clutches of millions of eggs almost simultaneously.
Why crustaceans migrate
Spiny 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 the fall, lobsters gather in a convoy of thousands of individuals and make a march from Bimini Island to the Big Bahamas Bank. So far, there is only one hypothetical explanation for this behavior: daylight hours begin to decline in autumn, which causes lobsters to change their habitat.
Prickly spiny lobster (Latin Panulirus argus) is also considered a nomadic representative of crustaceans. At the beginning of winter, it goes into deeper waters. Scientists have long believed that the reason for the movement of the spiny lobster is breeding, but it was later found out that egg laying occurs much later than migration, only after 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 ice age, when in winter they changed cold waters to warmer deep waters.
Spiny lobster migration is truly an amazing sight! Several hundred individuals move in columns one after another. What is most interesting, spiny lobsters maintain constant contact with each other. So, the one who is behind holds his antennas on the carapace of the one who goes in front.
Examples of insect migrations
Butterfly Danaida monarch (lat. Danaus plexippus) - the most famous inhabitant of North America. During periods of animal migration, she is seen in Ukraine, Russia, the Azores, North Africa. In Mexico, the state of Michoacan, there is even a monarch butterfly reserve.
On the issue of migration, this insect also distinguished itself: Danaida 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 animals migrate for generations.
Diabase is the reproductive phase that danaida enters, born at the end of summer, which allows the butterfly to live about 7 months and reach its wintering place. The monarch butterfly has an amazing “solar sensor”, which allows the third, fourth generations to return to their wintering sites of their ancestors. Interestingly, the most favorable climate for these butterflies was in Bermuda, where some insects remain year-round.
European species also migrate. Burdock, for example, winter and breed in North Africa, and already their offspring moves to the north and takes out the summer generation, after which it again flies to Africa. In spring, history repeats itself.
Interestingly, burdocks 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 5,000 km! And their flight speed is rather big - it is 25-30 km / h.
Some butterflies do not migrate continuously, but only depending on the conditions. These include urticaria, swallowtail, mourning, cabbage, admiral. All these species live in Northern and Central Europe, but can move south under adverse circumstances.
But oleander brazhnik, for example, annually makes a move from Turkey and North Africa to Eastern and Central Europe. These butterflies breed there, but, unfortunately, in the winter, most of their offspring die. In the spring, the next generation migrates from the south.
Short conclusion and conclusions
So we figured out a bit 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 came in the jungle. All animals were drawn to the only rivulet where parity was to be observed: all are equal, hunting is a taboo. Such migration occurs, as a rule, within the habitat when animals (most often inhabitants of the steppes, semi-deserts, deserts) during a drought migrate 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, vultures), which need to be close to the feed base. Thus, food and water make large groups of animals of several species 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 the range of habitat, others cover thousands of kilometers to achieve a favorable climate; the third radically change the habitat (remember about sturgeon and European eel).
Yes, migrations of various animals have a different nature, different reasons, but all have one thing in common - the thirst for life.