Storks flying from Poland to Africa prefer spenidng nights on buildings and trees but what do they do when there is a lack of such comfortable places?
According to the analysis of data from transmitters of 90 birds during their first migration, storks tend to spend nights simply on the ground. There are also many indications that storks are not disturbed by light: sometimes they sleep under street lamps.
During the annual migration, storks travel thousands of kilometers. This requires them to be physically and intellectually prepared: after all, they must know where and how to get to Africa. In the press release sent to the media, the authors of the study point out that the young, inexperienced individuals have the worst experience which travel the route for the first time and have to reach a safe wintering area. It is known that it is impossible to fly all the time, especially when the flight is demanding and the method of displacement needs to be optimized. It’s a bit like driving a car or flying by plane – you need to refuel, eat and even rest on the way.
In the context of this spectacular migration feat, scientists wanted to better understand the strongly connected issue of the journey, namely sleeping.
“Birds definitely need breaks but it’s not that simple because during a break, birds are on land and it is much more dangerous than the air”, comments Ph.D. Piotr Tryjanowski from the University of Life Sciences in Poznań, quoted in the press release sent to the Science in Poland website. “But there is probably a sleep break because it is known that the brain is less alert then and they need to find a suitable place to sleep and be ready for the next day in the air.”
The researchers wanted to check how storks choose places to sleep.
“What is much more interesting, we need to know whether this dream can be disturbed. And if so, by what factors.”, Ph.D. Tryjanowski, Co-author of a work published in the Journal of Avian Biology, devoted to the migration of white storks says.
The research was carried out by scientists and naturalists, analyzing information about the places and times of overnight storks for 90 storks (from the southern part of Poland) during their first trip to Africa. 41 of them reached the destination but unfortunately, the rest died (8 at night). Migratory birds preferred to spend the night on buildings and trees, but when there were no such birds, they spent the night on the ground.
“The choice of accommodation is quite a simple matter. We can simply observe the birds ending their trip in the evening and gathering several on the roofs of houses, trees or even electricity poles.”, Ph.D Piotr Profus from the Institute of Nature Conservation of the Polish Academy of Sciences in Krakow adds.
Analysing whether the stork woke up during sleep or even moved around requires much a more advanced technical and analytical approach. The new methods come to the rescue on this matter, for example, transmitters set up on storks, equipped with sensitive GPS-GSM technology, enabling the tracking of even very slight movement, the authors of the publication report.
“The transmitter itself weighs about 20 grams, which is less than 1% of the bird’s weight, and its capabilities are really amazing. It is thanks to the use of these devices that we have learned a lot about what happens to Polish storks when they leave our country.”, Joachim Siekiera from the Silesiana Group. He was responsible for setting up transmitters and checking their technical condition says.
Ph.D Łukasz Jankowiak from the University of Szczecin states that “only a transmitter and signal are not enough”. Thus, scientists have to process and locate the obtained data in space. It is also necessary to combine information about the bird’s life with the influence of specific environmental conditions. This requires an analysis of gigabytes of data. Scientists noticed that the birds slept most restlessly at the very beginning of their migration.
“Surprisingly, at night they moved less near artificial light sources, i.e. near illuminated streets or courtyards.”, Ph.D. Jankowiak reported.
“It seems that, paradoxically, young storks perceive artificial light as a bit of peace, or at least it makes them less exposed to predators’ attacks. So far, the information about predators’ attacks on sleeping birds is only anecdotal but it was certainly an extremely important selection factor in the past.”, the researchers conclude.