Climatic variation affects seasonal survival of an alpine bird species

We studied willow ptarmigan in a montane landscape in Lierne municipality in central Norway. During the study we captured and marked a total of 272 willow ptarmigan from 2015 to 2021. To capture the birds, we approached them from snowmobiles during the winter night, dazzled them with spotlights and then captured them with dip-nets. We then equipped the captured birds with a VHF transmitter with approximately 30 months battery life, and monitored them by use of VHF triangulation by foot, skis, or snowmobile, and occasionally by aircraft. This method enabled us to track the survival of individual birds throughout the study period.

By following these birds over seven years and monitoring their survival in relation to variation in snow patterns during spring and autumn, we found that snow patterns affect the survival of this common northern mountain species. When winter arrived early, the mortality risk for yearlings increased in the following spring, suggesting that a tough autumn has carry-over effects into the following seasons. Further, spring mortality was higher for both adults and yearlings when there was much snow in the spring. By demonstrating how changes in snow patterns can affect the mortality risk of this alpine species, our study gives increased insight into species-specific sensitivity to climatic change.

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