Climate change causes Bewick’s swan to winter closer to home
When autumn is mild, Bewick’s swan do not fly as far south. This was shown by researchers from the University of Amsterdam and the Netherlands Institute of Ecology (NIOO-KNAW) by following individual swans for several years. “Climate change makes it possible for species like the Bewick’s swan to shorten their migration route.”
Bewick’s swans (Cygnus bewickii) seem to be fair-weather campers. On their way south, they perch where the temperature is right. Due to climate change, the birds are wintering increasingly farther north and thus closer to home. Five questions about bird migration to UvA PhD student and principal author of the research on Bewick’s swans, Hans Linssen.
It has long been known among biologists that migratory birds adjust their flight routes due to climate change. Why has it only now been proven?
“Until now, those studies were always conducted at the population or group level: we see that the winter range of a species shifts as a whole. But then you don’t know whether that is because individual birds change their behavior within their lifetime or because a younger generation of birds suddenly decides to winter farther north than their parents.”
“Traditionally, swans and geese were thought to be stationary and winter in the same place every year. For this reason, the shift in wintering habitat is sometimes explained as a generational change: young birds look for a different wintering site than their parents and then stay there for their entire lives. We wanted to investigate whether individual birds can also change their destination and to what extent this is indeed driven by temperature and climate change.”
“To do this, we followed 55 Bewick’s swans for several years with GPS transmitters. This showed that the Bewick’s swan is actually very flexible during its lifetime and changes its wintering place every year depending on the temperature. That flexibility appears to be an important driver of the Bewick’s swan’s shifting winter range.”
So the choices of young swans don’t necessarily differ from those of their parents?
“We can’t say that for sure at the moment: we think there are jumps between generations in addition to the individual shift in wintering range. As far as I’m concerned, that’s the most exciting question now. To what extent do young swans mimic their parents, and to what extent do they go their own way? We are now going to look at that in a follow-up study with more transmitter data of complete swan families, parents, and their young. We hope to be able to say something about that in a year or two.”
Is the Bewick’s swan disappearing from the Netherlands?
“That seems to be the case. The Netherlands and southern England used to be the epicenter of this small swan’s wintering grounds, but climate change has already shifted that to northern Germany. In the Netherlands in the mid-1990s there were about 20,000 Bewick’s swans in winter; now there are just under 4,000. That number will probably continue to decline. We now see that the first Bewick’s swans continue to winter in Estonia. At the same time, other species are coming to spend the winter in the Netherlands. For example, the little and great egret, originally more southern species, can actually be found more often in the Netherlands with our increasingly warm weather.”
Is it bad if wintering areas - of migratory birds in general and the Bewick’s swan in particular - are shifting?
“Climate change allows species like the Bewick’s swan to shorten their migration route. But not all birds have the luxury of flying shorter distances when temperatures rise. For example, many wading birds must return to the Wadden Sea every winter because they depend on the shellfish and worms found in the seabed there.”
“For the Bewick’s swan itself, it is not necessarily bad. In winter the Bewick’s swan lives mainly on farmland with crops such as corn, sugar beets, and potatoes; or grass. That food can be found throughout much of northwestern Europe. Although, of course, we would like to continue to see the Bewick’s swan in the Netherlands. There are Natura 2000 targets to stabilize the Dutch winter numbers and also maintain them in the long term, based on the quality of the habitat here...”
“At the same time, the Bewick’s swan breeding area on the coast of the Barents Sea in European Russia also seems to be moving northward. There they may run into a problem because they are already up against the coast and cannot go much farther. Some Bewick’s swans migrate to the northern archipelago of Nova Zembla to breed, but who knows if all the birds can go there? That area will become more popular as more and more migratory birds feel compelled to go farther north.”
Why do birds want to breed so far north in the first place?
“That actually comes down to the question of why birds migrate, one of the big questions of migratory ecology. The main reason is probably to avoid competition and disease. There are fewer animals in the Arctic and fewer diseases and parasites because it’s colder.”
