Simulated present distribution (AUC = 0·953; k = 0·763)
Simulated late 21st century distribution (R = 0·55; O = 0·47)
Most of this species’ European breeding range is in Arctic areas with annual temperature sum < 1000 degree days above 5°C and AET/PET ≈ 1·0; no coldest month mean temperature limits are apparent here. In oceanic, and especially ‘Alpine’ areas, its range extends to regions with temperature sum of up to ca. 3300 degree days, some seasonal moisture deficit (AET/PET ≥ 0·8), and coldest month mean temperature between 0°C and 7°C. It is likely, however, that this apparent extension to warmer drier areas is an artefact of using the mean elevation climate to fit the model.
The response surface model has a ‘very good’ fit. Discrepancies include failure to simulate most Pyrenean localities and too many simulated occurrences in the Arctic islands. The simulated future potential distribution is shifted northwards. More localities in Franz Josef Land and Novaya Zemlya are simulated as suitable than at