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Migration of Birds: Following Sunsets?

> Why They Migrate

> Marshlands, deltas and lagoons

> Feathers, the Birds' Clothes


dimarts, 27 d'abril de 2004
A team of North-American scientists have conducted a study with the aim of discovering how migrating birds are able to travel thousands of kilometres and arrive at the same place year after year. The conclusions they have reached are pretty surprising, as you are about to discover.

The study, directed by William Cochran, at the Illinois Natural History Survey, was based on the analysis of the migration of a group of thrushes in the American Midwest on their annual journey towards the lands in the north.

The experiment began with the capture of a group of thrushes, which were fitted with radio transmitters. Basing itself on the hypothesis that birds use the Earth's magnetic field to orientate themselves, they were released after being exposed to an artificial magnetic field pointing east.

And what was the result? Well, that the birds flew east, disorientated by the artificial magnetic field.

Then, at nightfall, they corrected their flight to a northerly direction, which has allowed them to formulate the hypothesis that the light birds receive from the setting sun also has an influence each day, when it comes to flying in a particular direction.

Why They Migrate


+ The phenomenon of migrations is present in all classes of the animal kingdom.
As you know, the phenomenon of migrations is not exclusive to birds, but is present in all classes of the animal kingdom. Basically, there are two reasons to explain why many species of animals decide to embark on these long journeys. The first, and most obvious, is the scarcity of food or water, caused especially by the changing seasons or climatic variations. This is the case with many herbivorous mammals, which, whether because of the winter cold or because of drought, move in groups towards new pastures. The other can be found in the life cycle of animals, which moves them to head towards a suitable habitat in order to reproduce. A well-known example of this is the salmon, which swims back up the river to breed.

Marshlands, deltas and lagoons


+ The Ebro Delta, a magnificent example of nature reserve.
Wetlands like marshlands, deltas and lagoons play a very important role in bird migration. Many birds make a stop, whether to rest from the long journey and set off again with their energy renewed, or whether to nest, meaning, by making a nest, incubating their eggs and raising their chicks. Our country is one of the most important stopping off areas and breeding areas for birds in all of Europe. There are the magnificent examples of nature reserves such as the Ebro Delta (the most important wetland area), the Aiguamolls of Empordà, the Albufera of Valencia and the Albufera of Majorca.

Feathers, the Birds' Clothes


+ Many birds change their plumage during the spring and summer.
Plumage is a characteristic exclusive to birds, and has some varied and unusual functions. They protect them from possible injury and from the cold, at the same time that they help to reduce the air friction while they are flying. Also, the colouring of the feathers is of great importance, as much because it allows them to recognise each other, as because it allows them to display themselves. In this sense, many males, with the end of courting the females in mind, change their plumage during the spring and summer; plumages of all colours, which contrast with those they display during the winter, of much more sombre tones. Not for nothing, do many people call this type of plumage nuptial.

MATERIALS

  • Ocells migradors
    Format:Web
    Monogràfic sobre ocells migradors que conté, entre més coses, una llista detallada dels ocells estiuencs del Principat.
  • Birds
    Format:Web
    Pàgina de la British Broadcasting Corporation (BBC) sobre ocells: fotografies, articles, sons...
  • National Geographic Kids
    Format:Web
    Espai de la National Geographic Society adreçat a la xicalla.
  • Aula de natura
    Format:Web
    Un espai ple de natura dins l'escola.
  • Fitxes d'ocells
    Format:Web
    Una sèrie de fitxes d'ocells, amb mapes que n'assenyalen l'extensió geogràfica.

QUE HO SABIES?

  • Wings allow birds to fly, but not all of them. Penguins use them to swim and the ostrich has to content itself with walking since its wings are so small.
  • Birds come in all shapes and sizes. The tallest is the ostrich, which can grow to up to 2.5 metres, while there are others, like some humming birds, which grow no taller than six centimetres.
  • Ornithology, the branch of zoology which studies birds, is a highly developed science, which is the origin of progress in very diverse fields, like biology, ethology and orientation mechanisms during migrations, such as the example we are reading about now.

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> Causes de les migracions animals.
> El misteri de les migracions dels ocells.
> El cant d'ocells diversos.
> La fauna del Parc Natural del Delta de l'Ebre.
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