Questions & Answersback

How and why do birds flock together (e.g. Starlings):
    - have they an appointed meeting place? 
    - what is ‘black sun’ – and how do migratory birds find their way?

Answer: Black Sun is a natural phenomenon that occurs in spring and autumn when huge flocks of starlings gather in marshland areas before migrating.
The starlings come from all the countries around the Baltic and Norway. Presumably it is the weather that triggers their need and instinct to head south, as it happens immediately before the first frost of winter.
Just before landing for the night, the huge flocks of starlings draw fascinating patterns in the sky. Referred to as Black Sun, the phenomenon is a form of training before the actual migration itself, which is seldom witnessed as it takes place at night.
It is probable that over thousands of generations the starlings have learned that it is safest to migrate in one large flock (just as herrings protect themselves by swimming in large shoals). And the fact that they chose the South West Jutland coastal mudflats is no coincidence either, as the area provides sufficient food for the thousands of starlings. Added to this is the fact that many birds prefer to migrate along coastline areas.

Observations and studies have shown that birds use different navigation systems that vary from species to species. Another factor is whether the migratory route is hereditary, acquired learning or a mixture of both. Large birds that migrate in flocks often use an acquired or partially acquired migratory pattern. Geese are an example of this. The young birds learn the migratory route by following the older birds. Geese often have established resting areas, which are visited year after year on their way north or south.

The stork is an example of a bird that follows a migratory route that is both learned and hereditary. Normally the young storks follow the adult birds when they migrate south. In this way they learn the migratory route. Studies have shown, however, that young storks that for one reason or another become isolated from the flock, can find their way again. Other studies show that acquired migratory patterns are stronger than hereditary ones. This means that young storks will always follow the adult stork if they are close by. This is the case in Sweden, where for many years storks have been raised and released into the wild in the hope of attracting a large stock population. Unfortunately what has happened is that the old storks do not migrate but instead winter in Sweden. The young storks therefore stay in Sweden, which was not quite the objective of the exercise.

Birds that follow hereditary migratory patterns must have some kind of compass that enables them to establish their direction. Many studies have shown that the birds have different kinds of ‘compasses’. Some birds may only use one kind of compass while others use several kinds. When it comes to determining the migratory direction of birds, scientists measure their migratory unrest under different conditions. In practice this involves placing the birds in a funnel equipped with an inkpad at the bottom and blotting paper at the sides. A bird that shows a great deal of migratory unrest will constantly hop up and down in the same direction, which is seen as a ‘footprint’ on the blotting paper. There are also other less subtle methods for determining the birds’ migratory direction.

We know that certain birds use the sun and stars by which to navigate. In order to navigate using the sun, birds must have an inner clock. They simply have to know the time – and they do. Scientists discovered this using a simple method. They placed the birds in a funnel and then placed the funnel in a room with an artificial sun or sky. By moving the sun or the sky the scientists discovered that the birds moved too. If, for example, they moved the sun ten degrees, the birds altered their direction by the same amount.
Some migratory birds navigate using the earth’s magnetic field. The earth is surrounded by magnetic lines that form a special pattern around the earth. Somehow the birds are able to use this pattern and thus use the earth’s magnetic field by which to navigate. This has also been corroborated by putting the migratory birds in a funnel and then placing the funnel in an artificial magnetic field. When the magnetic field changed, the birds changed direction.

Carrier pigeons and certain sea birds use smells to navigate but scientists continue to disagree about the importance of this olfactory ability.