Species distribution areas and abundances are moving northwards towards the cold North Pole due to climate change. A new study shows that the abundance shifts of bird species vary between habitat types during the winter season in Finland. The strongest northward shifts have been observed on arable land compared with forest and urban areas. Although the annual occurrence of species can vary substantially, the range margins of 81 bird species have shifted an average ca. 40 kilometres northwards since the 1990s.
Researchers from the University of Helsinki found that snow is likely to be a more important factor than temperature in influencing species’ abundance shifts. Snow cover can constrain access to food resources for birds in winter, and thus, reduced snow cover due to climate change may cause abundance shifts of species.
“Snow cover is more critical in open habitats, such as on arable land, where the birds forage on the ground, compared with forests, where food can be found from trees”, explains researcher Laura Bosco from the Finnish Museum of Natural History, University of Helsinki.
Finland typically shows a clear gradient in snow cover, with thicker cover towards the north and east. Overall, the shifts were stronger in north-east directions – where snow cover had reduced most over the last decades. However, species and their reactions to climate change are often unique, to where responses to snow conditios depended on the habitat they overwinter in.
“Range shifts were strong in species that preferred no or less snow cover such as the yellowhammer and house sparrow. In contrast, species that regularly winter in snow-rich conditions, such as the great spotted woodpecker and crested tit, moved less”, says researcher Purabi Deshpande from the University of Helsinki.
Based on earlier findings, snow conditions can also affect the habitat selection of bird species during winter, to where arable land is preferred over urban areas if the snow layer is thin or lacking.
The study was based on Finnish winter bird counts (in Finnish), where habitat-specific data have been collected since 1986 from hundreds of routes across the country by volunteer birdwatchers. The first winter bird counts were conducted in the winter of 1956/57, and the 67th mid-winter count season began Christmas 2022 when birds were to be surveyed along more than 600 routes. The surveys are coordinated by the Finnish Museum of Natural History and BirdLife Finland. The study was published in the international research journal Oecologia.
Bosco, L., Xu, Y., Deshpande, P. et al. Range shifts of overwintering birds depend on habitat type, snow conditions and habitat specialization. Oecologia 199, 725–736 (2022). https://doi.org/10.1007/s00442-022-05209-5