Rapid elevational shifts of Switzerland's avifauna and associated species traits

Global change in climate and land use has profound effects on species’geographic and elevational distributions. In European birds, while species arepredicted to track their climatic niches upslope, lowland agricultural intensifi-cation and high-elevation land abandonment can drive elevational shifts. Spe-cies traits that can predict response to change in climate and land use caninform conservation, but a thorough examination of their relationships withelevational shifts in European birds is lacking. We estimate the change in theelevational distributions of 71 species from 1996 to 2016 in a region of thewestern Palearctic with wide elevational gradients (approximately 3000 m)and large changes in temperature. We model the relationships betweenelevational shifts and species traits associated with resource preference andadaptive capacity at five reference points including the cool edge, warm edge,and the core of species’elevational distributions. When intermediate referencepoints were removed, changes to the results were negligible, indicating thatthree reference points are likely sufficient. We found significant upslope anddownslope shifts in 56% and 23% of our study species, respectively. Asymmet-ric rates of shifts in the cool and warm edges caused significant contractions inelevational extent in 30% of our study species. The effect of elevational prefer-ence (i.e., midpoint elevation) was habitat dependent. Movement in alpinebirds was unidirectionally upslope, with nearly half displaying significant orapparent elevational range contractions. In woodland birds, asymmetries ofshifts in reference points led to expansions in extent in low-elevation speciesand contractions in high-elevation species. Generally, migrants, species withsmaller mass, smaller relative brain size, smaller hand-wing index, andgeneralists in diet, habitat, and elevation had greater upslope shifts. Whileelevational shifts in European birds were heterogenous and species-specific,many were rapid, and species traits associated with resource preference andadaptive capacity were associated with common patterns of elevation.