The flocks that could be seen over Bonn are the cranes that take the western route towards the south. It leads over the Moselle River in the Voreifel into the wetlands of France or into warmer weather in Spain. Cranes coming from northern Russia fly the eastern route to the south. It leads over the Bosporus and the Mediterranean Sea to Northern Africa.

Under favorable flight conditions, cranes can fly to Southern Europe without a stop. "The birds reach a speed of about 65 kilometers per hour," says Peter Meyer of the Nature Conservation Union (Nabu) Bonn. So they can cover a good 600 kilometers in one day.

Fluctuations in the weather like storms or heavy rains, however, force the cranes to take a rest. One of the largest resting places for cranes is the Lac du Der in the French Champagne region. "Up to 40,000 birds rest there at a time," says Meyer. In Germany, too, there are large resting places for migratory birds, one near Linum, one in the Diepholzer Moorniederung in Lower Saxony and the National Park called Vorpommersche Boddenlandschaft. But also in between stops, cranes are often forced to find a temporary resting place. "Cranes are herbivores and usually look for harvested fields," explains Meyer. They can already recognize them from the air. According to Meyer, the farmers do not take additional precautions for resting migratory birds. It is not necessary because the cranes usually find enough food left on the harvested fields. "In Sweden, extra feeding areas for migratory birds are prepared by putting out corn," says Meyer. Up to 50,000 birds stop to feed.

Having arrived in Spain, the majority of the birds have reached their wintering grounds. Only few cranes still move on to Northern Africa. The flight paths have become rather shorter in the last years, several thousand cranes even spend the winter in Germany now. The cork oak forests in Spain offer the birds plenty of food and safe winter quarters. "This area is endangered, however, since more and more forests are planted with holm oaks," says Meyer. Anyone who drinks wine should make sure that the bottle is sealed with genuine cork. That way, the cork oak groves remain and are a safe haven for migratory birds.

The first, smaller flocks already took off at the beginning of October, the last ones are expected to start in mid-November. In flight, cranes fall into a V-shaped formation with experienced and strong animals at the head. As soon as the bird at the front gets tired, they change places so it can conserve energy. Behind the tip of the formation, families fly with their young. Once in the wintering grounds, the flock separates and reassembles before the next flight. The composition is based on the location of the birds. However, pairs of birds usually stay together.

The trumpeting calls of the cranes do not necessarily mean that icy cold weather and winter-like temperatures are imminent for Bonn and the region. "The birds orient themselves to the length of the day when they decide to start out rather than the weather forecast", explains Nabu spokesperson Meyer. "But they don't want to take that chance either.”