Switzerland – the place to be?

A recently published study the Swiss Ornithological Institute was involved in pinpoints the causes of this Europe-wide loss of biodiversity. Population trends in 28 countries paint a clear picture: agricultural intensification was identified as the strongest driver of decline, followed by increasing urbanisation. The effects of farming practices and urbanisation are not limited to the species typically associated with these habitats, but also affect long-distance migrants, in particular, and species dependent on insects to feed their chicks, in general. It is reasonable to suppose that besides the direct effects of habitat loss, indirect factors such as a reduced food supply and the impact of pesticides are harming the continent’s birds.

If you compare population trends within Europe, Switzerland looks like a positive outlier at first glance. The various indicators that make up the Swiss Bird Index all show more positive trends than their European counterparts. The «SBI® Regular breeding birds», for instance, declined along with the European «Common Breeding Bird» index until the early 2000s, but has since increased, while the European index continues its downward trajectory. For 65 % of the 108 species represented in both indices, short-term trends (2013– 2022) are more positive in Switzerland than in Europe as a whole. Of the 50 species whose populations declined during this period in Europe, as many as 32 have a rising trend in Switzerland. They include farmland birds like Red-backed Shrike and Eurasian Wryneck. How is it possible that many species seem to be defying the large-scale declines in a country as densely populated and intensively farmed as ours?

The reasons for the difference between the European and Swiss trends are complex. Many species suffered dramatic population declines in the 20th century or have already disappeared completely, among them Woodchat Shrike, Grey Partridge and Ortolan Bunting. While after their disappearance, these species no longer contribute with further negative trends in Switzerland, their overall European populations continue to dwindle. At the same time, some species are recovering in our country thanks to conservation action (e.g. White Stork, Common Whitethroat) or are only now colonising Switzerland in significant numbers due to warmer temperatures (e.g. European Bee-eater). What looks like a favourable overall trend is therefore partly the result of many populations declining to a low level while others have shown strong growth (e.g. Rook, Red Kite).

In Alpine areas, climate warming is happening at an above-average pace. Rising temperatures allow many lowland species to move higher up and colonise areas where they were not present in the past, or only at a low density. An added advantage for farmland birds is that higher-elevation sites are often not managed as intensively as lowland areas. We see evidence of this in the «Monitoring of common breeding birds» data: 60 % of the 97 species that were recorded over an altitudinal gradient of at least 1000 meters show more positive trends at higher elevation than lower down. The set includes 19 farmland species, of which 13 have more positive trends higher up, such as White Wagtail and Whinchat. Gains at higher elevation can compensate the negative trends, some of them marked, on the Central Plateau, thus stabilising the overall trend.

At the end of the last ice age some 12 000 years ago, the lowlands of Europe were mainly tundra. When the landscape changed and became uninhabitable for species like Rock Ptarmigan, they took refuge in the high mountains, where they have sustained their populations to this day. Today, Europe’s breeding birds face a similar outlook. For many species, human activities have resulted in large-scale losses of breeding habitat, and continue to do so. Climate change has allowed some bird species to colonise higher altitudes, where more natural habitats can still be found, or to colonise them in greater density than before. Such movements to higher ground are not possible in large parts of Europe due to a lack of high mountains. Mountain regions therefore have a special responsibility to preserve biodiversity, not only with regard to alpine species, but increasingly for lowland species as well. Whether or not the Alps will once more serve as a refuge in the Anthropocene depends also on how we exercise our responsibility. Should climate change and agricultural intensification continue to progress in mountain areas, further losses in the future seem likely.

References
Rigal, S. et al. (2023): Farmland practices are driving bird population decline across Europe. Proceedings of the National Academy of Sciences, 120(21), e2216573120.