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"Through San Blas the stork you will see and if you do not see it, snowy year" or "Through San Juan the stork begins to fly" are some examples of typical sayings that refer to the migration of, in this case, storks, such as indicative of a specific time of year. Like all sayings that have their origin in popular knowledge, it is a very interesting idea, since these migrations of animals are very common and there are many who carry them out, but do you know why they do it exactly? Besides storks, do you know other animals that also migrate?
In Ecologist Verde we have decided to help the reasoning of these expressions about migration and their meaning so, if you want to know more, stay in this article about which are the animals that migrate and why.
What is animal migration
First of all, what is migration? What does it consist of? Migration is neither more nor less than the displacement of a population periodically from their original habitat to another where they settle for a certain period of time. These migrations are phenomena that occur in nature to maintain the ecological balance or balance of all the ecosystems that participate in this event, both the departure and arrival ecosystems as well as those intermediate through which these migrant individuals pass.
These animal migrations are studied in various fields, such as ecology, biogeography or zoology.
Migrations usually last several days depending on the distance they have to travel and are different between the different species that carry them out. For example, birds often use the trade winds and other air currents, while other smaller animals such as amphibians or invertebrates also take advantage of water currents.
On the other hand, migrations are not usually individual events, but rather animals usually migrate in groups. However, what is really unknown even today is how these species that travel great distances they are able to orient themselves until they reach their destination, there are various theories such as, in the case of birds, the orientation of the Sun and the stars. Theories that take the Earth's magnetic field as a reference are also considered.
Why do animals migrate
Once we know what migrations are, the big question comes. Why do animals migrate? It seems that this behavior it is something instinctive in the species that carry it out.
Migrations are linked to certain events to fulfill different purposes, but as a common denominator to all of them we find the main objective of all forms of life: survival.
The 3 fundamental objectives of migration are as follows:
- Temperature differences between the different seasons of the year. This is perhaps the most well-known reason of all, and it is that species migrate due to these changes in temperature, which become very low during winter and, on the contrary, very high during summer, so that species they move away and ensure their ability to survive in other areas during these extreme periods.
- Reproduction and foraging. It may not be so obvious, but many animals are forced to move away from their usual habitats to mate safely or to look for food in other areas where competition is not as high.
- Flee from their predators. Again it is not one of the first reasons that comes to mind, but it is something logical. The animals move away from those areas where they feel threatened by other species and look for new shelters where they can protect themselves.
What animals migrate - examples
There are many migrating animal species, from birds to reptiles and fish, among others. Next, we are going to delve a little more into each of the groups of animals that migrate and we will discuss some examples. Attentive!
Migrating birds
Birds are the ones that usually travel, generally, the greatest distances during their migratory journey, such as the shearwaters (seabirds that can fly up to 910 km a day), the swallows or the small golden plover.
In addition, birds can be classified according to when they migrate, that is, what time of year they decide to move away in a specific place. Taking the Iberian Peninsula as a reference, we can distinguish between wintering birds that flee from the cold north and spend the winter here on the peninsula, such as the common crane (Grus grus); summer birds that, on the contrary, flee from the heat of Africa like the common swallow (Hirundo rustica) and spend the summer here; or birds of passage.
Other examples of migratory birds are:
- The White stork, which migrates to Africa in winter avoiding crossing the Mediterranean Sea, which is the most striking part of its migration period. The reason? It seems that the winds from which they are helped that we discussed above only occur over land areas.
- The canada goose, one of the typical ones that form V groups in the skies during migration. This species prefers and seeks warm climates, as well as better availability of food sources.
Migratory fish
Some species of fish also migrate, the most famous being Salmon migration. Many species reproduce in fresh water, where the young of the fish develop that once they reach adulthood migrate to the sea where they grow, feed and mature sexually. Finally they return to the rivers, which they cross against the current to reproduce in them.
Something similar, although, on the contrary, it happens with eels European and North American. In their adult state they live in rivers, but they go to the Sargasso Sea during the reproductive season.
Other examples of species that migrate annually are herring, cod or flounder.
Amphibians and reptiles
Some species of sea turtles, as green turtles carry out migrations. They live on the coasts near Brazil, but they travel great distances to spawn on the beaches of Ascension Island (in the South Atlantic Ocean). These hatchlings quickly go to the sea and, over time, appear on these Brazilian coasts where the adult specimens live and feed. Some examples are loggerhead turtle, olive ridley turtle, olive ridley turtle, leatherback turtle (the longest, more than 4,831 km from their nesting beaches).
On the other hand, newts, frogs, toads and salamanders they also carry out annual migrations of a few kilometers. In these cases, migration occurs from those places where they hibernate during the winter to rivers or ponds where they reproduce later.
Mammals that migrate
Some well-known examples of migrating mammals are wildebeest, zebra, caribou, antelope or elephants. These animals migrate to find food sources and wells of water to survive.
Another example is seals, California sea lion or whales, like the humpback whaleMegaptera novaeangliae), the southern right whale (Eubalaena australis) or the gray whale (Eschrichtius robustus). These whales can travel up to 20,000 kilometers during their migrations between their feeding and breeding grounds.
Invertebrates
Although we usually forget about them, invertebrate animals also carry out migrations related to the search for food and the reproductive season.
A particular case is that of plankton, which performs daily "vertical" migrations. During the night the plankton is found in the most superficial layers of the water of the seas and oceans where it feeds and with the arrival of the day it descends up to 1,200 meters to flee from its predators and reduce its metabolism due to the lower temperature of the waters. deeper, saving energy.
Some examples of invertebrates that migrate best known are:
- The crabs, which move to salty waters to lay their eggs, covering distances of up to 240 kilometers.
- Lobsters, known for the great damage they cause to many crops in their path.
- The butterflies like the monarch butterflyDanaus plexippus), which you can see in the image below, whose migration lasts longer than the life of any other species of butterfly (it can live up to 9 months) and which takes them to travel more than 5,000 kilometers from the northern part of the United States and Canada to Mexico and California. Migration begins between August and October and they remain at their destination until March, at which time they return to the north. They are thus one of the few insects that can make transatlantic voyages.
- Dragonflies belonging to the genres Libellula Y Sympetrum, that migrate in massive groups of individuals. Highlights Pantala flavescens with the longest transatlantic migratory journeys of all insects (longer than the monarch butterfly). Travel between India and North Africa, round-trip, traveling up to 15,000 kilometers.
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