Animal Migration

In the animals, the migration is a phenomenon present at many species, which carry out a displacement (even a tour), often on long distances, in periodic matter which implies a regular return in the starting area. The movements without return, which lead to an extension of the habitat of the species, correspond rather to a phenomenon of Colonisation.

The migrating ones and reasons of the migration

It occurs in general at periods of changes of climatic conditions, but it is actually due to the variations in the availability of food.

Thus, the Oiseau X migrating do not leave to seek the sun but to find a food abundant. The fact that the migration occurs with the change of season marked the popular spirit at the point to create proverbs like one swallow doesn't make spring . The return of the migratory birds in the areas moderated there to nest and reproduce is explained by the less presence of predatory and a less competition during the collection of food with the other species.

The principle of the migration for the Poisson S and the marine mammals is the same one: the species will seek the food resource and safety where they are, according to the seasons.

Other animals also migrate: large mammals (caribou, Gnou…) like some butterflies.

Migratory ways

The routes of migration answer the requirements and the aptitudes of the various species; some follow shores, banks or rivers, gather to pass the collars, the Isthme S or Détroit S, whereas others spin right, under the seas, or while flying over deserted and oceans. The roads thus followed cross and are recrossed weaving a very complex network around the Planet. The concept of biological Corridors gathers these axes of migration, but also of the natural axes of (Re) colonization or circulation in the matrix écopaysagère.

During their way, certain birds are directed with the sun, more exactly they are sensitive to the Ultra-violet S emitted by the sun (visible even through the clouds). The birds can be also directed with the moon, the stars and by the Terrestrial magnetic field, it is the case of the Pigeon S which seem to have a Boussole intern. Certain insects are sensitive to the incidence of the rays solar or returned by the moon. Other species or the same ones use the odors or of the Infrason S to be. Those which already carried out several migrations undoubtedly have benchmarks in the landscape. It was shown that at certain species of birds or mammals which travel in group (the Oies for example) the young people learn with better locating themselves during their first migrations.

The means used by the animals to find their road until destination still are very badly included/understood.

The voyage

The migrating ones generally leave after having made full the with energy, because their way will generally not leave them the occasion find enough food, in particular at the time of the overflight of the deserts and the mountains or the seas for the migratory birds. This energy is stored in the form of grease, which will be consumed in the course of road, the famished and exhausted animals often arriving at destination. When the reserve of grease is insufficient, the animal can die of exhaustion before achieving its goal.

If the phenomenon of the migration of salmons and eels is known since thousands of years, that of the birds was not really proven at the end of the 18th century thanks to the bush setting of the birds. The migration of many insects, bald person mouse and the marine mammals has been studied only for a few decades. the follow-up by satellite made it possible to specify certain migrating roads and to prove that the voyage outward journey differs from the voyage return and that within a species, groups can follow very different ways to join the same site. To species of butterfly of North Africa the adults migrate towards the far North at year N. They die there after having laid, and the following year, it is the new generation which migrates towards the south.

Passive or undergone migration

Certain species can travel carried by animals (Phorésie), it is the case of the Rémora which clings to the Requin S, Raie S or turtles, and many external or internal Parasite S or species symbions. Those which are transported (Phoronte S) by the migratory birds, of migrating fish or the marine mammals travel sometimes quickly and far.
D' others still are passively let carry by the water currents, it is the case of many planktonique larvae of the Océan S.

The follow-up of the migrations

See also: System of positioning by satellites

The Balise S of followed by satellite are used to follow, for example the migratory birds or the tortoises lute since the end of the Années 1980 and have provides information impossible to obtain before, their precision is about 150 Mr. the beacons beacons Argos are very much used, in 1997, they weighed surroundings 80 grams. In 2006 they weigh only between 16 and 30 grams. If the transmitters GPS are available since the beginning of the Années 2000, they were miniaturized to be able to be fixed on the migratory birds only in the middle of the decade. The precision of localization is then about 10 Mr. By providing regular measurements, these beacons allow teaching or scientific projects such as followed it on line movements on Internet. In 2005, the weight of a transmitter GPS is of 70 grams.

See too

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