Snow conditions effect habitat choice for wintering birds

Deep snow cover increases the number of wintering birds near human settlements but reduces numbers in arable fields, according to a new study of the University of Helsinki.

Climatic conditions can influence species' habitat choice, said the university in a press release on Wednesday referring to the study.

In northern regions, climate change is not only reflected in changes in temperature, but also in snow conditions. A new study looked at how changes in snow depth are influencing birds’ habitat choice.

Researchers at the University of Helsinki have noticed that decreasing amount of snow in South and Central Finland has lead into increased number of birds feeding on arable fields since 1980s. The deeper the snow, the fewer birds were observed in fields, but the more birds wintered near settlements.

“Deeper snow cover prevents birds from foraging in fields, and supplementary feeding in settlements provides an important food source for wintering birds," said Purabi Deshpande, a PhD researcher at the University of Helsinki.

Overall, the number of wintering birds has increased in Finland. However, bird numbers changed differently in different habitats. Numbers increased by 70% in fields since 1986, but decreased by a fifth in settlements. Different species also reacted differently.

“Our study shows that less snow does not always mean more birds - it depends on their behaviour. Migratory birds such as the whooper swan or the common gull showed the strongest responses. Their abundance in fields was high in winters without snow, but some of the birds moved further south in snowy winters,” said Associate Professor Rose Thorogood of the University of Helsinki.

Species that live in Finland year-round can also change habitat due to snow, the study found.

For example, jackdaws and yellowhammers may feed in fields when there is little snow, but birds will aggregate in settlements when there is a snowstorm. Snow explained species' habitat choice better than temperature.

“This past winter has been mild overall, but snow-rich in most parts of the country. Climate change will continue to increase bird feeding opportunities in fields, but intermittent snow cover also attracts birds to settlements,” said Aleksi Lehikoinen, Senior Curator at the Finnish Museum of Natural History, Luomus, University of Helsinki.

The study was based on winter bird counts coordinated by Luomus and BirdLife Finland with hundreds of volunteers across Finland. The results were published in the Journal of Biogeography.