Climate Change Predicted to Trigger an Upward Altitudinal Range Shift and Boost the Abundance of a Montane Rock Face Specialist, the Wallcreeper (Tichodroma muraria)

Montane species are predicted to respond to climate change by moving upslope, particularly high elevation specialists with thermal niches adapted to cold environments. Unfortunately, the accuracy of predictive species distribution models is often reduced by (1) the challenge of accounting for changes in habitat and resource availability and (2) the inability to account for complex life history strategies. Here we use the Wallcreeper (Tichodroma muraria) as a model species for predicting the response of high elevation specialists to climate change, leveraging unique aspects of its ecology as an obligate cliff specialist and altitudinal migrant. Using species distribution models based on citizen science data collected across Switzerland and intensive field surveys of abundance within its core range, we predict future range shifts and overlap among life cycle periods under different climate change scenarios. Principal environmental predictors varied among seasons, with temperature being more important during the winter. While the breeding range was predicted to shift upwards with little change in overall spatial extent, the overwintering range was predicted to expand upslope by up to 244%, leading to a 123% increase in seasonal overlap. Abundance models showed similar results while also providing the first robust density estimates for the species in Switzerland. In contrast to past studies of alpine biota that predict severe range contractions due to climate change, sufficient high elevation habitat exists in Switzerland to allow the Wallcreeper to shift and expand its range upslope, especially in the overwintering period when cold thermal constraints are relaxed. However, most of the current Wallcreeper distribution in Europe lies in mountain ranges likely to be outside of its breeding thermal range in the future, stressing the importance of the Swiss Alps as a stronghold for this species and alpine diversity in an era of rapidly warming temperatures.