animal migration (in English: Animal migrationIt is a concept in biology in which organisms move to places that provide them with better living conditions.^[1][2][3] Many birds, fish, insects and mammals migrate regularly to avoid unfavorable changes in climate or food sources. People also migrate, but they often migrate for political or social reasons and they may also migrate for biological reasons. See: human migration.

Biologists use the term migration to describe many movements. Some biologists – especially entomologists – consider departure without return as migration, as some animals leave a place in search of better living conditions and do not necessarily return with their offspring to the places from which they migrated. Other biologists describe the historical changes as migrations. But most biologists define migrations as regular, circular movements by animals between two areas, each of which provides better living conditions for one stage of the animal’s life than the other. This type of migration is the subject of this article.

These migrations take place on land, in water, or in the air. Some animals migrate only short distances, as many frogs and toads migrate annually regularly for a distance of kilometers between their breeding places and other places, while other birds migrate thousands of kilometers annually. The longest migratory bird is the polar hook, which migrates for a distance of about 35,000 km annually.

Types of migration[عدل]

Most migratory animals perform two types of migrations:

1- daily migration

2- Seasonal migrations, while other migratory animals make one or a few circular migrations during their lives.

daily migrations[عدل]

Zooplankton in the oceans perform this type of migration, swimming hundreds of meters underwater during the day and returning to the surface at night.

seasonal migrations[عدل]

These migrations occur twice a year. They are associated with seasonal changes in temperature or the level of precipitation. There are three types of seasonal migration: 1- Trans-latitude migrations, 2- Vertical migrations at heights, 3- Local migrations.

Bats, seals and many migratory birds migrate across latitudes. They mainly migrate in a north-south direction, while some mountain animals do vertical migration up and down mountains across mountain slopes. For example, Alpine snow partridges and red deer spend the summer high in the mountains and descend into the valleys in the winter. The majority of tropical birds and mammals perform local migrations, migrating to wetter places in times of drought and returning to their homes at the onset of the rainy season.

The least frequent migrations[عدل]

Some animals do this type at intervals; Salmon fish, for example, are born in the upper reaches of rivers, but soon migrate to the oceans. After many years, they return to the places where they were born upstream to breed. Pacific salmon die immediately after spawning, but some Atlantic salmon return to the ocean to spawn, and do so three times during their lifetime. Female sea turtles also make such migrations to lay eggs several times during their lives. Female green and female loggerhead turtles swim every two or three years for a distance of 2,000 km to the sandy beaches where they hatch to lay their eggs.

Why do animals migrate?[عدل]

Migration enables many animal species to exploit areas with favorable weather and abundant food, or to mate at certain times of the year. For example, food is abundant in some regions of the world in the summer, but it is less or non-existent during the cold winter months. Accordingly, many of the animals that live in these places migrate to warmer regions during the fall, but return in the spring when the weather becomes warmer.

Many animals migrate to breed in certain places that provide their young with the best chances of life during certain times of the year. Migratory birds breed in their summer refuges where food is available, while humpback whales migrate from their polar feeding grounds to give birth in warm tropical or subtropical waters. These waters provide little food for the large whales, but the young ones do not tolerate the cold of the polar waters.

What drives immigration?[عدل]

Migration begins in most animals with the onset of unfavorable environmental conditions, but it is difficult to explain the reasons for migration in some other animal species. Many migratory birds may leave their roosts in the tropics even though conditions are still favorable for them to stay there. The migration motive for these birds may be the environmental changes associated with the onset of warm weather and the increase in food in their northern breeding areas. Experiments show that the increase in the length of daylight hours is the cause of the migration of many species of birds, as this increase in daylight hours in the spring leads to the release of certain hormones in the bodies of those birds that push them to prepare for the vital migration to the north.

In addition to environmental indicators, many seasonally migrating animals may have a programmed calendar that God deposited in their bodies, telling them when to migrate. Some birds exhibit seasonal migratory behavior even when kept under constant environmental conditions in the laboratory. A programmed timer may control the bodies of salmon and other animals that migrate at different times in their lives, telling them when those migrations will begin.

How do migrating animals find their way?[عدل]

Research has shown that migratory animals use many methods to collect information that helps them determine their directions during migration, as many migratory animals use the sun, moon and stars to determine their migration path. These animals can monitor the movements of these celestial bodies to determine their path, while other animals use terrestrial phenomena such as coastal lines, rivers and mountain ranges.

In their migrations, animals depend on other properties besides the sense of sight in determining the path of those migrations, as salmon fish depend on the smell of the rivers in which they were born in determining their way back to those same places to breed in. Others are guided by changes in temperature, humidity, wind direction, or the Earth’s magnetic field. While marine animals use ocean currents.

Migratory animals use more than one compass to determine their directions during migration. Some types of migratory birds may be guided by the sun during the day and by the stars during the night. Many biologists believe that it uses the Earth’s magnetic field to determine its path on cloudy days and nights.

Sometimes, migrating animals are forced to change their natural path to places that are foreign to them. Some of these stray animals may be able to determine where they are and how to get to their places of origin. This process is called navigation. There are many ways of navigation in migratory animals that scientists know very little about.

Experiments conducted on sparrows, homing pigeons, and water clippers have proven beyond doubt the presence of navigation in migratory animals, as scientists hunted these birds from certain locations and took them to other areas thousands of kilometers away from their natural places, and most of these birds were able to return to the same The places where scientists hunted them.

Other experiments have shown that young animals can migrate, but they may not be able to navigate from strange places. For example, the European starling usually migrates southwest from its breeding grounds around the Baltic Sea to its wintering grounds around the English Channel. Scientists caught some large and young starlings that arrived in the Netherlands during their migration, and carried them to Switzerland, where they released them. The large birds were able to reach their perches around the English Channel, while the starlings that migrated for the first time continued to fly in a southwesterly direction, as some reached Portugal, some to Spain, and others to southern France.

Sources[عدل]

Comprehensive knowledge encyclopedia

On Commons, photos and files on: animal migration

• Zoology portal

Retrieved from «https://en.wikipedia.org/w/index.php?title=animal-migration&oldid=60330156»