Heat-loving species are on the rise in Sweden. Some species are becoming more common, and new species are coming from the south. The latter is about European species that can now manage with us thanks to milder winters and longer summers.
– Yes, we have undoubtedly gained more species in the last 20-30 years. Sweden has fewer species than, for example, in Spain or Italy, and this means that there is a pool of species south of us that can move up when suitable areas arise when the climate becomes warmer, says Åke Lindström, biology professor at Lund University who compiled inventories of 224 species.
More reasons
However, the heating is not the only reason, Åke Lindström points out. Birds may increase or decrease in number for other reasons, such as reduced hunting, disease, or changes in agriculture and forestry.
– But that the climate is a factor that changes our bird fauna, it is undoubtedly so, he says.
“Cold” species are pushed out
The warmer climate is not only good. The birds run the risk of falling out of step with the insects when they have to raise their young, as research on black-and-white flycatchers shows. Species that thrive better in a colder climate are also pushed back.
– In the longer term, there is a risk that we will lose some of our mountain birds, because the environments and the climate in which they thrive are decreasing in size, says Åke Lindström.
“Warm” species winner
Even the native bird fauna is changing. The researchers have divided all bird species into “cold” and “warm” species according to the temperature where they thrive best. It provides an index that shows that more people win than lose in the heat. Heat-loving species are increasing in number (for example, sedges) and are also spreading north (for example, chaffinch).
– We see that this indicator has gradually increased very clearly and in the last two years has had the highest values so far, says Åke Lindström.