The Odyssey of the Bewick’s Swan: traceable online from the Russian tundra to European coastal areas

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Bewick’s Swans, Lapscheure (Belgium). Image: D. Vangeluwe/RBINS
08/11/2021
The Odyssey of the Bewick’s Swan: traceable online from the Russian tundra to European coastal areas
post by
Kelle Moreau

Mystery in the world of the Bewick’s Swan: During the last 15 years, the numbers in the traditional wintering areas in the North Sea countries fell by a third, while in the Evros Delta (Greece-Turkey), a new area was colonized where the numbers rose to 9000 during February 2018. What is the origin of the swans in this new area? What are their migration routes? And is there a link with the decline in the North Sea area? The international ringing and transmitter program "The Odyssey of the Bewick's Swan" helps to answer these questions, and the movements of the tagged Bewick's Swans can be discovered online on a geographical application.

The Bewick’s Swan Cygnus bewickii is the smallest swan species in the world. It only breeds in the Russian tundra. However, the winter weather conditions do not allow a plant eater like the Bewick's Swan to stay in its breeding area the whole year round and force it to undertake long migrations. Traditionally, these migrations lead the Bewick's Swan to three widely separated wintering areas: the North Sea area, the southern shores of the Caspian Sea, and south-eastern China and Japan. In 1997, however, a fourth wintering area was discovered in the Evros Delta at the border between Greece and Turkey, one of the most natural coastal marshes in the Mediterranean.

Since this surprising discovery, the number of Bewick's Swans wintering in the Evros Delta has risen to 9000, which is very unusual considering that nowadays declines and extinctions of wild species are more often announced ... Or is there bad news as well? Indeed, the number of Bewick’s Swans wintering in North-Western Europe has fallen by a third in recent years. In the North Sea countries, the winter population is now estimated at less than 21,000 individuals (compared to about 30,000 individuals some fifteen years ago), and the negative trend seems to continue.

Mysteries of migration and wintering

The reasons for the decreasing number of Bewick's Swans wintering in the North Sea area are not exactly known. Some disturbing facts that may contribute are the relatively low number of young compared to their wintering counterparts in China and Greece, evidence of illegal hunting pressure despite the strict protection of the species in Europe and Russia (an English study illustrated that almost one in four wintering Bewick’s Swans contains shotgun leads), and observations of frequent changes in food type (linked to human activities, e.g. grazing, beets, potatoes, maize) which may indicate an unstable situation.

But the appearance of Bewick’s Swans in the Evros Delta is also surrounded by mystery. From which breeding grounds do they originate? Which route do they take between the Arctic and the Mediterranean, nearly 4000 km apart, and which resting places are important? Are individual Bewick’s Swans faithful to a particular wintering area, or is there a link between the decline around the North Sea and the increase in the Evros Delta? Transmitter research started in 2015, has taught us that at least some of the Evros swans breed on Russia's Yamal Peninsula, and occasional sightings of Bewick’s Swans marked in the North Sea area, in the Evros Delta indicate that some of them are able to change their wintering area, but the number of encounters is too low to draw any major conclusions.

Bewick’s Swans tracked online

The program "The Odyssey of the Bewick's Swan", which started in 2015, aims to contribute to solving these questions. As part of this program, Bewick's Swans are also ringed and equipped with GPS/GSM transmitters, both in the Russian breeding areas and in the Belgian wintering areas.

It is natural for us to share this data with the general public. The movements of the tagged Bewick’s Swans are visualized online on a geographical application. At the moment, the migration routes of 23 Bewick’s Swans, which were ringed in Belgium during the last 3 winters, can be found here. The routes of swans marked at different sites in Arctic Siberia (Yamal and Pechora) will soon be added to give a full picture of the very amazing migrations of this species, whose strategies are clearly evolving.

The data are updated weekly. However, no updates are made from mid-May to mid-September as the swans are breeding or summering in the Russian tundra, where they are out of range of GSM networks. However, the GPS location data are stored in the transmitter and are broadcasted as soon as the swans have a GSM reception again.

Getting started with the geographical application

To consult the data, log on to https://odnature.naturalsciences.be/bebirds/en/blog_swans, then click on the sentence "Follow the migration paths of birds equipped with GPS logger in our tracking application". You will then see an interactive map. The top line shows the date of the last update. By clicking on the "information" icon you will find a description of the program and the list of partners. By clicking on the "layers" icon and then on the triangle on the line "The Odyssey of the Bewick's Swan", you can view the characteristics of each swan tracked by the unique code of its transmitter collar. By clicking on the "filter" icon, you can retrieve the visualization of the route of a particular swan. To do so, enter the transmitter collar code in the "neckband" box and then click on "close" at the top right of the page. The "time manager" icon allows you to select a time period while selecting a particular swan.

Organization

The program "The Odyssey of the Bewick's Swan" and the web application visualizing the movements of the tagged Bewick's Swans is a joint effort of the Royal Belgian Institute of Natural Sciences (RBINS) and the A.N. Severtsov Institute of Ecology and Evolution (Russian Academy of Sciences), in collaboration with the Yamal Nenets Autonomous Okrug Government, the Research Center for Eco-Environmental Sciences (Chinese Academy of Sciences), the Forest Research Institute (Hellenic National Agricultural Research Foundation), the Goose, Swan and Duck Study Group of Northern Eurasia, and the Evros Delta Management Authority.

This work of prospecting, observation, ringing and equipping with transmitters, management, data analysis and presentation, and website organization is of course a real team effort! Thank you all, from Salekhard to Bellem, from Tielt to Moscow, from Beijing to Oud-Turnhout and Merksplas, from Damme to Surgut, from Alexandroúpolis to Veurne, from Ottignies to Thessaloniki!

Categories: Scientific News
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