Climate change threatens alpine birds worldwide with habitat loss, range shifts, changes in population densities, community compositions, and phenology. Alpine systems and their organisms may face disproportionately stronger influences of ongoing climate warming compared to many regions at lower elevations or in temperate or tropical lowland systems due to their proximity to freezing conditions. The upward elevational expansion of trees driven by climate warming is expected to strongly decrease open high-mountain habitats of Alpine specialists. Consequently, these species must either adapt genetically and physiologically to warmer and forested conditions within a few generations or their local populations will go extinct and suitable territories may open at still higher elevations (if there is habitat at higher elevations; otherwise these species become globally and ultimately extinct). If the habitat availability at higher elevations is also too small, genetic diversity and therefore adaptive potential and long-term survival of populations is strongly decreased and the extinction probability increased even further