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Birds - what makes them change their migratory route?

Dr. Wolfgang Fiedler, head of the Radolfzell ornithological station, was practically born into his profession. Born on the Mettnau peninsula, which is close to the station, Fiedler spent hours and hours watching birds as a child. Later, when he was at school, he worked as a volunteer in the ornithological station.

The head of the Radolfzell ornithological station, Dr. Wolfgang Fiedler, in his office. (Photo: Keller-Ullrich)
“My initial contact with research was when I sorted scientific newspapers at the ornithological institute,” Fiedler recalls who is the only person from Radolfzell at the station. He was not only interested in birds, but in all animals. During his biology studies, his initial interest centred on bats, but an offer to do his degree thesis on bird migration, in particular the birds of the Curonian Spit, a long, thin sand-dune spit that separates the Curonian Lagoon from the Baltic Sea, aroused his interest in birds and he decided to become an ornithologist. Nowadays, Fiedler is mainly interested in the behaviour of migrating birds. “Why do birds migrate, and where do they go?” is the question Fiedler is most interested in.

Birds as models

The Radolfzell ornithological station is located in Möggingen castle. (Photo: Keller-Ullrich)
Birds are extraordinary study objects because they are mobile and can choose an area that best suits them. The behavioural change of migration enables researchers to draw important conclusions, for example on the effects of climate change. It has been shown that an increase in temperature leads to birds travelling shorter distances. Some bird species do not fly as far south as they used to or they return earlier; others do not fly south at all and remain in the same area all year round.
Even though storks are not part of a research programme, the latecomer in the photo is nevertheless allowed to spend the winter in the institute’s animal park (Photo: Keller-Ullrich) © Keller-Ullrich
The researchers are mainly interested in the evolution of the migratory behaviour of birds. How is this regulated and how quickly can changes in migratory behaviour be determined? Birds are excellent models for evolutionary research because they are very conspicuous and can be easily observed. They have a relatively uniform shape but within this there are thousands of subspecies, explains Wolfgang Fiedler. They have different beak shapes or colours, differently coloured feathers (plumage), some of them can swim and others spend almost their entire life in the air. Despite some common traits typical to all birds, strong selection pressure has also led to considerable differences. One and the same species might even differ in the wing shape, which has adapted to different habitats. If the birds have to travel greater distances, they tend to have longer wings. If they only have to cover short distances to their hibernation areas, then short wings are sufficient. There is also the advantage that short wings are more manoeuvrable.

New strategy

Since 1998, the Radolfzell ornithological station has been part of the Max Planck Institute for Ornithology. Its logo is the silhouette of two blackcaps, birds that play a key role in many of the institute’s research activities. The small migratory bird stands out for having two different hibernation areas. One group of blackcaps flies to Spain and the other to England. Originally, all blackcaps flew south. They had no choice in the matter because the direction of migration is genetically determined. A bird is unable to decide to change the direction in which it hibernates. The first ‘trip’ to England must therefore have been an ‘accident’, a mistake in the birds’ migratory programme. Nevertheless, this mistake turned out to be an excellent strategy. The English love birds and many people feed them with fat/seed balls, meaning that the birds have no problem to survive the winter. The distance to England is shorter than to Spain, so the birds return much earlier and start breeding. Their offspring inherit the migration direction and also hibernate in England. For ornithologists, blackcaps are a stroke of luck as they have been able to witness the real-time evolution of two different groups of birds with different traits.

Investigating migration

A great variety of nesting boxes. (Photo: Keller-Ullrich)
The ornithologists depend on the help of volunteers who help to ring the birds. The Radolfzell ornithological station is a ringing centre for southern Germany and Austria. Every year, approximately 350 volunteers ring about 80,000 birds. The small ring on the leg of the birds is like an identity card, providing information about the origin of the bird and about its migration route. Data from the last 100 years have been brought together in a database and enable the analysis of long-term changes.

Details on the movement of birds is also important for gaining a deeper understanding of the spread of diseases, for example in the case of bird flu. Many epidemiologists and politicians were not aware of the fact that many birds do not migrate from north to south, but from northwest to southwest. Currently, the researchers are looking into the small-scale movements of birds.

Advice and information

Fiedler finds his work fascinating as it brings him close to biology and life, enabling him to understand the complexity of life in its entirety. He is also glad that his work is not only academic work but that it also brings him into contact with other people, for example with the many volunteers and laypeople who regularly contact the institute with specific questions. The most frequent question in summer is, “I think I have just seen a hummingbird. Do you think this is possible?” The institute’s staff has the answer off pat: “No, it was not a hummingbird but a hummingbird hawk-moth, moths about 5 cm in size, with a long proboscis. The moths hover and make a humming noise, two features that make them look remarkably like a hummingbird. Despairing car drivers contact Wolfgang Fiedler because of a wagtail that catches sight of its reflection in the lateral rear-view mirror. The animal, which believes that the mirror image is a competitor, becomes enraged and fights the enemy to the point of near exhaustion, thereby completely damaging the varnish of the car. The ornithologist has the solution for such situations: Cover up the mirror to make the ‘enemy’ invisible. 

Website address: https://www.biooekonomie-bw.de/en/articles/news/birds-what-makes-them-change-their-migratory-route