It’s the most exciting day of little Louis’ life: The young stork was born only six or seven weeks earlier in a birch tree in Radolfzell on the shores of Lake Constance. Until this day in June 2014, he had only known his parents and three siblings. But then, suddenly, curious beings appear at the nest to attach tiny transmitters to the four small white storks. They are Dr Andrea Flack and Dr Wolfgang Fiedler from the Max Planck Institute for Ornithology and the University of Konstanz. In the coming years, Louis and the other storks will transmit data that will help the researchers learn more about migrating storks and how they tend to follow individuals that are especially adept at exploiting thermal updrafts, which allows them to reduce the number of times they flap their wings. The more efficient travellers fly as far as West Africa, while the rest of the storks spend the winter in Southern Europe. The researchers will be able to tell which individual is going to fly where and how far only ten minutes after the storks’ departure. This data demonstrates for the first time that the flight performance, social behaviour and global travel routes of storks are interlinked. These new insights, resulting from the collaboration between researchers at the Migration and Immuno-Ecology department at the Max Planck Institute for Ornithology and those in the research area Collective Behaviour at the University of Konstanz, have now been published in the current issue of “Science”.
Andrea Flack and Wolfgang Fiedler have been scouring the western shores of Lake Constance for days. The fire brigade’s turntable ladder raises them up to the lofty heights of the stork nests, where the two researchers attach small tracking devices to the backs of the nestlings. These devices will allow them to track Louis and 60 other young storks as they migrate south. The transmitters, which weigh less than 60 grams each, record the animals’ exact location via GPS coordinates and measure their acceleration rates. In this way, the researchers can tell if and how the birds are moving.
For Louis and his siblings, the harmless procedure is over within a few short minutes. Since they are fully focused on perfecting their flying skills, they are likely to soon forget their strange encounter with the researchers. For the researchers, however, the work has only just begun: From here on out, their task is to collect and analyse huge amounts of data. During the first several days of the storks migration the transmitters take two- to five-minute second-by-second snapshots of the animals’ GPS coordinates every 15 minutes. Thereafter, the devices use the local mobile phone network to transmit a text message once a day for the entire lifetime of the birds, documenting the locations of the individual birds recorded at 5-minute intervals.
The data are automatically fed into the online database Movebank - a freely accessible online platform developed by a team led by Professor Martin Wikelski, which researchers from all around the world can use to log animal migrations. Since the storks from Lake Constance tend to fly to West Africa for the winter, the transmission of such large amounts of data would lead to extremely high mobile network costs. For this reason, Andrea Flack follows the birds during the initial phase of their migration in her car all the way to Barcelona, using a base station to download all of the data once a day. Once the storks reach Africa, the recording intervals are extended, which reduces the amount of data that must be transmitted.
A mobile phone for storks
Louis, too, received his “mobile phone” on that day in June four years ago. On 17 August, he left to travel south - the first among his nest mates - joining a group of 27 other birds. After five days, only 17 of the original group are still travelling together.
First, Louis follows the Alps, passing Bern and Lake Geneva and crossing the river Rhone south of Lyon. On the evening of 23 August, he reaches Montpellier on the French Mediterranean coast and, on the next day, follows the coast down to Spain. He traverses the Pyrenees and stays several weeks at a waste site north-west of Barcelona before forging on to Madrid and where he spends the winter at a nearby local landfill site. Louis remains in Spain until the spring of 2016, returning to Germany in March.
Looking for thermal updrafts
Never before have researchers been able to track the group flights of storks as meticulously as those of Louis and his peers. The results of Louis’ first five days of travel have now been published by researchers from the Max Planck Institute for Ornithology and the University of Konstanz. The data from this thousand kilometre long stage of the migratory flight demonstrates for the first time how the flight performance of a bird, its social behaviour and its global migratory route are linked.
A sophisticated analysis of the GPS data has revealed that lead birds guide the migrating stork groups through areas with favourable thermals, where the birds are literally sucked up by the rising warm air. This allows them to switch from active flight to gliding flight, thereby saving a significant amount of energy.
Efficient flyers lead the way
A detailed analysis of the high-resolution GPS data shows that the flight paths of the 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 analysed the data relayed by the transmitters. The follower birds then benefit from the leader birds’ experiences and sour upward in more regular trajectories. "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, an individual birds’ flying skills does not only determine its position within the group. The amount of time a stork can glide apparently also determines where it will spend the winter. Animals that flap their wings a lot more do not fly as far as those that can make better use of thermals. Louis, for example, is a rather mediocre flyer and has not yet become a leader. It seems to be more favourable for him to spend the winter in southern Spain - especially since he can find enough food at the landfill sites there.
Redrunner is another story. He was also equipped with a transmitter by the researchers from Radolfzell and Konstanz in the spring of 2014 and has since been tracked. He is able to get by with fewer wing flaps, belongs to the leaders of his group, and is able to reach wintering grounds in North Africa. While Louis covered more than 1,000 kilometres on his journey in 2014, Redrunner covered almost 4,000 kilometres. "The flight characteristics are so central to the bird’s 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 to West Africa," explains Andrea Flack.
This is the first time that humans have been able to observe the group behaviour of storks in such detail as they journey across Europe to Africa. The data collected by the researchers demonstrates that storks fly in socially structured groups that are strongly influenced 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 of the Max Planck Institute for Ornithology and Honorary Professor at the University of Konstanz.
Since 2014, Louis and Redrunner have repeated their journey every year. While they have not always ended up in the exact same location, Louis has remained faithful to Spain and Redrunner to Africa. This year, Louis arrived in Germany on 9 March. He lives in Neudingen near Donaueschingen where, together with his partner, he has built a nest on the local town hall. Redrunner also returned from Africa a few weeks ago. He has taken up residence in the town of Münzenberg between Frankfurt and Gießen.
Now as four-years-olds, they have both survived the most dangerous phase of their lives, as 75 percent of young storks die in the first year of life. They have also made it through puberty and may for the first time in their lives breed this year. If the two storks continue to successfully avoid all dangers, they can continue to undertake their long roundtrips for the next 30 years.
Should both Louis and Redrunner begin their next journey this fall, the researchers will not be following them to southern Spain in their car this time around: Martin Wikelski’s Icarus Initiative will be launched this August. From then on, the tracking devices will transmit animal movement data to researchers around the world via the International Space Station. Researchers will then be able to track the birds around the clock in real time.
Background information on the migration of storks:
The natural habitat of the white stork (Ciconia ciconia) during the summer months stretches from the Iberian Peninsula to Central and Eastern Europe all the way to the Ural Mountains. There are also populations in Turkey, the Caucasus and in Central Asia.
The so-called eastern white storks in Europe fly to Africa in the fall by crossing the Bosporus, the Jordan Valley and the Sinai Peninsula. Their wintering grounds are located in East or South Africa. They require one to one and a half months to complete the 10,000 kilometre trip.
The western storks fly over the Mediterranean near Gibraltar and spend the winter in West Africa between Senegal and Lake Chad. These birds return to their breeding grounds in the spring before the eastern storks do. The approximate boundary separating the eastern and western stork runs roughly from the Elbe to Upper Bavaria. Only a few birds select the middle route over Italy to Tunisia in North Africa.
From local collective behavior to global migratory patterns in white storks
Andrea Flack, Máté Nagy, Wolfgang Fiedler, Iain D. Couzin, Martin Wikelski
Science; 25 May 2018
- Researchers from the joint “Collective Behaviour” research initiative of the Max Planck Institute for Ornithology and the University of Konstanz are able to predict which storks are likely to migrate to Africa in the autumn and which ones are likely to remain in Europe.
- These insights have been published in the current issue of the scientific journal Science.
- The GPS coordinates of the animals are recorded.
- This data demonstrates for the first time that the flight performance, social behaviour and global travel routes of storks are interlinked.
Note to editors:
A photo and several videos are available for download here:
Stork flying towards a group of white storks in the field.
Photo: Christian Ziegler. Copyright: MaxCine, Max Planck Institute for Ornithology in Radolfzell
GPS data visualization of 27 storks thermalling elegantly in a thermal upwind. The flight path of each bird is colour-coded based on its overall flapping activity from blue (low) to red (high).
Animation: Renaud Bastien und Máté Nagy. Copyright: Renaud Bastien and Mate Nagy, Max Planck Institute for Ornithology in Radolfzell
Migration routes of storks during the first four weeks of migration. The GPS tracks are colour-coded based on the overall flapping activity from blue (low) to red (high); measured during the high-resolution data acquisition period (the first approx. 1000 km).
Animation by Máté Nagy. Copyright Máté Nagy, Max Planck Institute for Ornithology Radolfzell