Natures wonders: European stork migration patterns (Introduction)

by David Turell @, Friday, May 25, 2018, 00:26 (564 days ago) @ dhw

Some less adept fliers stay in Europe. The most proficient fliers go to Africa:

https://phys.org/news/2018-05-scientists-storks-migrate-africa-autumn.html

"Andrea Flack and Wolfgang Fiedler have been visiting storks' nests on the western shore of Lake Constance. The aerial ladder of the fire brigade raises them to the stork nests at lofty heights so that they can strap small tracking devices onto the backs of the nestlings. The aim is to follow Louis and 60 other young storks on their migration. The instruments, which weigh less than 60 grams, record the GPS coordinates of the birds' locations. They also measure the animals' movements using accelerometers. This allows the researchers to determine whether and how the birds are moving.

***

'Never before have researchers tracked a group flight of storks as meticulously as Louis and his peers. The scientists of the Max Planck Institute for Ornithology and the University of Konstanz have now published the results of Louis' and his peers' voyage. The data from the thousand-kilometre stage show how a bird's flight performance, social behaviour and global migratory route are interlinked.

"Thanks to a sophisticated analysis of the GPS data, the scientists have found that there are leader birds within groups of migrating storks. They lead the group to areas with favourable thermals, where the birds are literally sucked up by the rising warm air. This allows them to glide farther and avoid active flapping flight to save energy.

***

'Detailed analysis of the high-resolution GPS data shows that the flight paths of the leader birds are more irregular. "They are the ones who locate the thermals and search out the most favourable areas within them. "As a result, they have to adjust their flight paths repeatedly," explains Máté Nagy, who analyzed the data from the trackers. The follower birds benefit from the leaders' explorations and can soar upward in more regular trajectories.

"'When travelling to the next thermal, follower birds are a bit slower and lose altitude faster. To avoid falling behind the group, they must flap their wings more and leave the thermals before reaching the top."

"However, a stork's flying skill is not only linked to its position within the group. How much it flaps its wings also predicts where it will spend the winter. Animals that flap their wings a lot do not fly as far as those that flap less. Louis, for example, is a rather mediocre flyer. For him, it is better to spend the winter in southern Spain, especially since he can find enough food at the landfill site there.

"The situation is entirely different for Redrunner, another individual of the 27 tagged storks. He is one of the leaders of his group, and, therefore, manages to minimize his wing beats. He overwinters in North Africa. While Louis covered more than 1000 kilometres on his 2014 journey, Redrunner covered nearly 4000 kilometres. "The flight characteristics are so central to the birds' position within the group that we can predict just after a few minutes of migration flight whether it will spend the winter in Europe or fly on to West Africa," explains Andrea Flack.

"This is the first time that humans have been able to observe the group behaviour of storks on their journey across Europe to Africa in such detail. The collected data show that storks fly in socially structured groups, which are largely determined by the flying skills of the group members. "A stork's route and destination depend, among other things, on how efficiently it can fly," says Martin Wikelski, Director at the Max Planck Institute for Ornithology and Honorary Professor at the University of Konstanz."

Comment: In this case migration is by study of terrain and flying efficiency.


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