Bird migration is the journey that birds make twice a year from their breeding grounds to their winter habitats and back. The first migration is the spring migration. The birds then fly to their breeding area. In the breeding area, they make their nests, lay their eggs, and raise their young.
The autumn migration is the long journey they take to hibernate. The bird migration is mainly innate and the bird thus follows its instinct. The migration is also partly learned by the older birds. The younger birds often migrate separately from the older ones.
The life of birds is mainly determined by the length of the day and the available food. The initiation of bird migration is therefore mainly caused by the lengthening or shortening of the days.
If there is little food (especially insects, caterpillars, spiders, and worms) left in the autumn, this will also be a reason for the migratory bird to go on a journey. Often departing birds encourage others to make themselves travel-ready. Sometimes very severe winters still cause a hasty departure. Such a trait is called disruption.
Preparing for the trek
Before leaving, birds ensure that they build up fat reserves. They need a few weeks for that. A lot of energy is needed for the long journey and they get it from fat. Some songbirds eat so much that they can double their body weight before migration. The amount of fat determines how long a bird can fly without food.
Traveling with instinct
Orientation to sun and stars
Some birds fly straight to their breeding or wintering area. Others look for a place to forage for food along the way: plaster. The same species usually follows the same route. Land birds, for example, migrate along the coasts and gather at Gibraltar to cross the sea together.
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Birds that migrate during the day orient themselves on the sun, the angle of view that the sunlight makes. Even if it is always different along the way. They have a kind of internal clock that keeps them informed of day and night. Birds that migrate at night orient themselves by the stars. In cloudy conditions, they fly more calmly or interrupt their journey.
Earth’s magnetic field
Birds also use the Earth’s magnetic field in their orientation. A bird has so-called magnetite crystals in its head. These are magnetized by the light and therefore a bird can correct its route where necessary. Birds can also perceive infrasound. This sound is caused by the wind or waves. These sound vibrations are not audible to a human being.
Leclerc de Buffon
For centuries, bird migration was a mystery to humans. For example, Aristotle thought that birds, like frogs, crawled in the mud to spend the winter. It was not until the 18th century that GL Leclerc de Buffon made it clear that there was a bird migration.
Leclerc de Buffon was a French biologist, member of the Academie Francaise and the Academie des Sciences and head of the royal gardens of Louis XV. In his Histoire Naturelle (44 volumes) he wrote down everything that was known about nature at that time and also studied it.