The migrations are movements of groups of living from one habitat to another beings. It is a survival mechanism that allows animals to avoid negative conditions of their habitat, such as extreme temperatures or lack of food.
The animals that migrate usually do so on a regular basis, that is, they do the same round trips at certain times of the year (for example, in the spring or fall). In other words, migration follows a pattern.
However, permanent migrations may also occur .
When a group of animals is taken by man from his natural habitat to a new one, it is not considered migration, since it is not a natural process. In those cases it is called “introduction of alien species”. The migration processes are natural events that keep the balance ecosystem involved in the process (the initial ecosystem, intermediate ecosystems by passing migrant groups and ecosystem that receives the end of travel).
On the contrary, the introduction of alien species artificially has both expected and unforeseen ecological impacts.
Migration involves biotic factors (animals that migrate) and abiotic factors that are used by animals, such as air currents or water.
Some abiotic factors can also be triggers of migrations, such as variations in light and temperature that occur with seasonal changes.
Examples of animals that migrate
- Humpback whale (yubarta) : Whale that travels through all the oceans of the world, despite large temperature variations. During the winter they remain in tropical waters. Here they mate and give birth to their young. As temperatures rise, they move to polar waters where they feed. That is, they transit between feeding sites and breeding sites. They travel at an average of 1.61 km per hour. These trips reach the distance of more than 17 thousand kilometers.
- Turtles : Turtle that lives in temperate seas, but in winter migrates to tropical or subtropical waters. They spend most of their time in the water and the female only goes up to the beach to spawn. They can live up to 67 years. It is a large species, reaching 90 cm long and weighing 130 kg. To make their migration, they use the currents of the North Pacific. They have one of the longest migration routes, compared to other marine animals, reaching more than 12 thousand kilometers.
- White stork : Large bird, black and white. European groups migrate to Africa during the winter. It is striking that in this route avoid crossing the Mediterranean Sea, so they make a detour to the Strait of Gibraltar. This is because the thermal columns that you use to fly are only formed on terrestrial areas. Then continue to India and the Arabian Peninsula.
- Goose of Canada : Bird that flies in groups forming a V. It reaches a wingspan of 1.5 meters and a weight of 14 kilos. Its body is gray but is characterized by black head and neck, with a white spot on the cheeks. He lives in North America, in lakes, ponds and rivers . Their migration takes place looking for warm climates and availability of food.
- Common swallow (Andorina) : It is the swallow with greater distribution in the world. Bird that lives in Europe, Asia, Africa and America. It expands together with humans because it uses structures built by humans to build nests (reproduction). Live in open areas such as pastures and meadows, avoiding dense vegetation, steep relief and urban areas. When migrating they also choose open areas and the proximity of water. They fly during the day, also in migrations.
- Sea lion of California : It is a marine mammal, of the same family of the seals and the walruses. During the mating season it is found on islands and coast from southern California to southern Mexico, mainly on the San Miguel and San Nicolás islands. At the end of the mating season, they migrate to the Alaskan waters where they feed, traveling more than eight thousand kilometers.
- Dragonfly : It is a flying insect capable of transoceanic migrations. Mainly the species Pantala Flavescens performs the longest migration of all insects. The route is round trip between India and East Africa. The total distance traveled is approximately 15 thousand kilometers.
- Monarch butterfly : It has wings with orange and black patterns. Among insects, this butterfly makes the most extensive migration. This is because it has a longevity much higher than other butterflies, reaching 9 months. Between August and October he migrates from Canádá to Mexico, where he stays until March, when he returns to the north.
- Wildebeest : It is a ruminant of a very particular appearance, similar in appearance to a hair but with hooves and head more similar to those of a bull. They meet in small groups that in turn relate to each other, creating large conglomerations of individuals. Their migrations are motivated by the shortage of food and water: they look for fresh grass with the change of season as well as rainwater. The movement of these animals becomes spectacular due to the intense sound and vibrations in the soil that produce their migrations. They make a circular trip around the Serengeti River.
- Dark shearwaters (dark shearwaters) : Sea birds that live in the Atlantic, Pacific and Indian Oceans. It measures 45 cm long and with its wings extended more than a meter wide. It is blackish brown. It can fly up to 910 kilometers per day. During the breeding season, it is found in the southern part of the Atlantic and Pacific Oceans, on small islands around New Zealand or the Falkland Islands. At the end of that time (between March and May) they begin a circular route to the north. During summer and autumn it remains in the northern hemisphere.
- Plankton : They are microscopic organisms that float in water. The type of migration carried out by marine plankton is of much shorter periods and shorter distances than other migratory species. However, it is a significant and regular movement: during the night it remains in shallow areas and during the day it descends 1,200 meters. This is because you need surface water to feed, but you also need the cold of deep water to lower your metabolism and thus save energy.
- American reindeer (caribou) : It lives in the north of the American continent and when it begins to rise the temperature migrates towards the tundras that are even further north, until it begins to snow. That is to say that they are always kept in cold climates but avoiding the times of snowfall when the food is scarcer. The females initiate the migration accompanied by the young offspring before the Mays. It has recently been observed that the return to the south is delayed, probably due to climate change.
- Salmon : Different species of salmon live in rivers during youth, then migrate to the sea in adult life. There they grow in size and mature sexually. Once they have matured, they return to the rivers to spawn. Unlike other species, the salmon does not use the currents for its second migration but quite the opposite: it moves upstream against the current.
- Newts, frogs, toads and salamanders also perform annual migrations of a few kilometers. In these cases the migration occurs from those places where they hibernate during the winter to the rivers or ponds where they reproduce later.
- Crabs , which move to salty waters to lay their eggs traveling distances of up to 240 kilometers.
- Lobsters , known for the great damage they cause to many crops in their path.
- Butterflies like the monarch butterfly ( Danaus plexippus ), which you can see in the image below, whose migration lasts longer than the life of any other butterfly species (can live up to 9 months) and that leads them to travel more than 5,000 kilometers from the northern zone of the United States and Canada to Mexico and California. Between August and October the migration begins and they remain at their destination until March, when they return to the north. They are thus one of the few insects that can make transatlantic trips.
- Herring, cod or flounders