Every year we are fascinated by the migrating cranes. Many details about migration have been discovered: Here are the most important of them:

Periode of migration
 Spring: January - March
 Autumn: September - November
Direction of flight
 Spring 90 % NE
 Autumn 95 % SW
Various
 Flying altitude 300 to 1.000 m
 Flying speed 40 to 133 km/h
 Time of day at any time of the day

When there aren't any disturbance cranes are migrating in a wedge-shaped formation. Flying in this formation the leading bird has to do a hard job. Because of this fact the leading bird has to be replaced by another one from time to time.
The steps of this change can be traced backwards on the drawing on the right. (The first and the following leading bird are marked by a circle.)

Weather and migration
Cranes orientate themselves by the predominating weather conditions and seem to be informed about them very well. Because of this they are able to decide - as a rule correctly - whether to continue migrating in spite of low visibility or to look for a resting place. Rainy and foggy weather conditions obstruct migrating cranes and force them to stay.
In the German air space they migrate rather exactly on an axis from Rügen in north-east Germany to Luxembourg / Saarland (Germany).
Well-known resting and assembling places being located on this small passageway are approached determinedly. Adverse weather conditions have the consequence that the migrating cranes have to put up with making a detour in order to reach their destination.
The masses of the cranes migrate when there are wind speeds of 0 - 12 knots. As the main direction of the wind is north-east most cranes migrate with crosswind.

Size of migrating flights
The size of the migrating flights changes permanently: Smaller flights assemble, big flights disintegrate into smaller ones. Only on days with much cranes migrating, on so-called days with mass-migration, bigger flights stay together for longer stretches.