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Dieren en planten

Animals   Birds   Waders   Bird Protection   Raptors and owls   Swimming birds   Songbirds   Other birds   Bird migration   

Water en land

Mens en Milieu

The east Atlantic migration route, Ecomare

Bird migration

Bird migration is a massive movement of bird species which occurs twice a year: in the spring and autumn. Millions of birds then travel up to many thousands of kilometers from their breeding grounds to where they spend the winter and vice versa. Many birds found in the North Sea and Wadden Sea are migratory birds. Waders, ducks and geese that breed and raise their young in more northerly regions, flee the cold in the autumn and migrate south. Some of them will overwinter in the Netherlands, others migrate further south. They use the tidal flats only to fill their bellies for the second part of their long journey to their winter home. In the early spring, they stop by again during their voyage back to their breeding grounds.

  • Why do birds migrate?

    In springtime, there is lots of food to be found in the breeding areas on the tundra in the high north. Since it hardly gets dark in the summer period, the birds are able to forage practically 24 hours a day. Naturally, that is very advantageous when you have lots of hungry chicks to feed. Because the number of predators is limited, it is also safer. However as winter approaches, the insects, spiders and worms crawl down deep and grass and seeds get covered under a thick pile of snow. The days start to decrease and the birds need more and more energy to stay warm. That is the reason that birds migrate in the autumn from their breeding grounds and spend the winter in more southerly regions, where it is warmer and there's plenty of food to be found.

  • Follow the stars

    Bird migration has been followed by people since olden days. Migratory birds use the position of the sun during the day and the stars at night to orient themselves during migration. Scientists made this discovery by using mirrors to manipulate the sun's position as was visible for the birds. The birds reacted by choosing a different migration route. Birds also use rivers and canals to orient themselves. Furthermore, the magnetic field of the earth and polarized light also play a role.

  • Radar contrle

    In Leeuwarden, radar from the Air Force keeps track of where birds fly. The radar can observe birds up to dozens of kilometers away. Eventually, the Air Force wants to make a model that can predict bird migration in order to avoid collisions between birds and airplanes. Birds can cause deadly accidents and lots of damage to airplanes.

    The images on the radar are also used by scientists. On the basis of the radar images, they have discovered that birds are capable of adapting their migration route to weather conditions.

  • Migration of land birds
    Migrating geese, Foto Fitis:www.fotofitis.nl

     

    Land birds migrate at high elevations. They don’t like flying over large bodies of water. The best place to see them is by sea straits, where the necessary crossing is the narrowest and is used the most often. You have a good chance of observing lots of migratory land birds every year in the north of Texel (by De Cocksdorp). In the autumn, one can literally pick them off of the beach and bushes. The birds are so exhausted; they need to catch their breath after the wide crossing. This is also where they gather in groups in the spring, using it as a pit stop before re-crossing the North Sea.

     

     

     

  • Seabird migration

    Seabirds usually migrate in one stretch, without stopping to forage. They eat while flying. The birds tend to fly low over the sea surface, in comparison with land birds that fly high in the sky.
    Seabirds build up much fewer fatty reserves for migrating than land birds. The advantage is that they are lighter in weight, which costs less energy to fly.
    It is more difficult to establish the route seabirds take compared to land birds. If they are not brooding, many species of seabirds wander over the seas. Some species, such as the manx shearwater, consciously leave for a specific destination, in this case Brazil.

  • Refuelling on the flats
    Godwits on the flats, Jeroen Reneerkens

    Migratory birds must keep to a strict travelling schedule. Should they arrive too late at their nesting grounds, it could mean that the young do not mature enough by the end of the summer to make the long voyage south. If they arrive too early, everything is covered in snow and ice and there's nothing to eat. Furthermore, it is of vital importance to bring along enough of their own fuel reserves. Many tidal flat birds use the rich feeding grounds in the Wadden Sea to build up their reserves in the form of fatty layers and heavy muscles. In the spring, these reserves are used to fly north as well as to survive the first period in the nesting area and to lay eggs. The Wadden Sea not just an arbitrary place along the migration route, but an essential intermediate station, where millions of birds ‘tank up’.

  • Always the same route?

    Spring migration is not necessarily the same route as in the autumn. For example, common terns migrate in the autumn just off the coast of Africa, where the most sardines can be caught. In the spring, sardines are found more in open sea. The terns adapt their route accordingly so that they can continue to catch sardines along the way.

  • Migrant or resident bird

    Birds that don't migrate are called resident birds. These birds stay in the same area the entire year. Whether or not a bird species migrates is genetically determined. In earlier days, people had very different ideas about migrating birds. In the MIddle Ages, they believed that birds changed into other species in the winter, such as the cuckoo into a sparrow-hawk, or that swallows hid in the mud. Some Middle Age birds flew to the moon or changed into fish.

  • Dangerous!

     

    Bird migration is not without risks. All kinds of danger lies along the route. Exhaustion due to bad weather or lack of food are naturally risks. But there is also a chance of being shot by a hunter, flying into powerlines and wind turbines. Every year, millions of birds die during migration.

     

  • Green lights

    Migrating birds can become extremely confused by artificial light. That is why drilling platforms at sea cause problems for birds during migration. Due to the large amount of white light in an otherwise dark environment, passing birds flew for hours in circles around the platforms until they dropped dead into the sea from exhaustion.

    Scientists discovered that birds are particularly attracted to the red particles in the spectrum of white light. Green light was much less confusing for migrating birds. Therefore rigs at sea, as well as harbors, are switching over more and more to green light.