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Migratory Behavior: The Early Bird

The early bird gets the worm. This well-known proverb has taken on a new meaning for a team of researchers led by Dr. Gernot Segelbacher from the Faculty of Environment and Natural Resources of the University of Freiburg and Dr. Martin Schäfer from the Faculty of Biology – with regard to the season rather than the time of day. They are studying the Eurasian blackcap as an example of bird migration.


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( © Ralph Martin)


The researchers have discovered that the earlier beginning of spring in the past 20 years has also led Eurasian blackcaps to arrive earlier in Germany. But to what extent is the migratory behavior of birds innate? What enables them to adapt to new circumstances? Eurasian blackcaps do not fly as far in the fall as cuckoos or storks: They are short-distance migrants and travel from Central Europe to Spain, England, or the southeast Mediterranean. In a study published in the journal Plos One in 2013, the scientists determined that birds with a preference for winter vacation on the British Isles are genetically distinct from their relatives that go on holiday in the south. Birds that migrate to Western or Eastern Europe, on the other hand, have a similar genetic makeup – despite the fact that they migrate in different directions.

  • Claw Samples and genetic analyses
To learn more about the relations between migratory birds, the researchers captured Eurasian blackcaps at breeding areas in Freiburg and at nine other locations in Europe. They took blood samples of the birds trapped in their nets and carefully cut off the tip of their claws. The blood samples enabled the researchers to determine the degree of genetic distance between the blackcaps. By analyzing the claw samples, they found out where the birds has spent the winter, as they contain different isotopes of hydrogen depending on the composition of the bird’s diet.
“The blackcaps that migrate to the southeast and to the southwest exhibit hardly any genetic differences. That is because the birds mate with each other, resulting in a more diverse the gene pool ,” says Segelbacher. The researchers still do not know what leads the birds to migrate to Spain or to the Balkans. The birds in eastern Central Europe prefer the eastern Mediterranean region or East Africa, while those in Western Europe prefer Spain.
  • A model animal for behavioral genetics
“In Freiburg we catch most of our birds in the Mooswald forest. Ten percent of the Eurasian blackcaps are English; the rest fly to Spain. That remains constant year after year, explain Segelbacher and Schaefer. Eurasian blackcaps are among the few birds of Central Europe whose population in Germany is steadily increasing. Is this due to their migratory behavior? The blackcaps didn’t discover the England route until around 50 to 60 years ago. Behavioral researcher Andreas Helbig used this example to demonstrate that migratory behavior has a genetic basis: He mated English blackcaps with Spanish blackcaps.


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The researchers caught black caps in Freiburg and 9 other locations in Europe (Credit: Martin Schäfer)
The hybrids flew to the Gulf of Biscay – the middle course between Spain and England. A reason why the genetic differences are very large is because the hybrids do not survive well there. “Besides, the English and Spanish blackcaps usually don’t mate at all, explains Segelbacher, “The English blackcaps arrive in Germany earlier and have long since found partners by the time the Spanish ones arrive.”
  • Is flexible best?
Whether Spanish or English, Eurasian blackcaps enjoy an advantage over other migratory birds: They are more flexible in when they fly to Germany as they have a shorter trip than species like cuckoos or storks, which migrate all the way to Africa. “Perhaps that’s why their population is growing,” suspects Segelbacher. The earlier growth of plants also has a harmful effect on many other birds that cannot change the time of their arrival in Germany and the time at which they reproduce. “Titmice are dependent on the massive appearance of caterpillars in May to feed their young,” says Segelbacher. If they start incubating their eggs too late and their young don’t hatch on time, they miss out on the proverbial worm. Thus, the researchers are studying how some animal species adapt quickly and successfully to changes in the environment, while others are left behind. “Most bird species don’t have this luck: Many species are endangered in Germany,” explains Segelbacher.




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PD Dr. Gernot Segelbacher

Gernot Segelbacher works as researcher at Wildlife Ecology and Management Department of the Faculty of Environment and Natural Resources of the University of Freiburg since 2005. After completing his biology degree at University of Tübingen in 1996, he became a doctoral student at the Technical University in Munich. In 2002 he finished his PhD about genetics of the capercaillie.  Until 2005 he worked as post doctoral scientist at the Vogelwarte in Radofzell and the Max Planck Institute for Ornithology. On his blog  he writes about the research in his lab.










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