Magnus Hellström is manager at Ottenby bird station on Öland and runs the association birdlife.
He has noted clear changes in recent decades as the average winters in southern Sweden have become both shorter and milder.
- In short-migrating species, there is a driving force not to move further than is necessary.
When the winter climate allows that there is food for the birds and that you can get by, there are many individuals who immediately try it, says Magnus Hellström.
What birds is it about?
- Today we have large populations of geese that winter in the southernmost parts of the country.
This did not exist a few decades ago.
In principle, all geese and also whooper swans flew down to the European continent.
Other birds that hibernate are blackbirds, which are often seen in gardens around Sweden these days.
The same goes for robins and wrens.
- When I was little, you had to look for a very long time to find these birds in January and February.