A northward shift in the spatial distribution of bird to track the climate have been widely documented as for other groups. Unfortunately many species are not are not fast enough. Indeed, the climate change velocities (the measure of the local speed of displacement of climatic conditions), that are strongly variable (complex effects of latitude, longitude, elevation, landscape, and land use) can be are locally very fast and bird populations are submitted to many intrinsic and extrinsic constraints.
However, these climate change velocities could have very different biological consequences in the same region and should depend on the topographic context. For example, to keep up with a 1°C increase, a poleward displacement in flat areas would require a 100 km displacement, while only a short shift uphill (around 100 m) could be sufficient in mountains. Hence many populations, in mountain landscape, show a change in the elevation limits of their distribution and track easily their thermal niche. These elevations are major concerns for biodiversity conservation because they can induce an increase of extinction probability, particularly about endemic or rare mountain bird species as in other groups. So, elevation could be like an attractor (because it is locally to easier to track climate), with two kinds of effects, depending on mountain orientation. The south-north oriented mountain could help the population to track their climatic niche acting like a corridor. However, in the case of the east-west mountain the attraction of elevation could allow some species to find a refuge site but for other species, and in function of climate scenario, these refugees could become traps (as a cul-de-sac) and be associated with an important risk of biodiversity loss. Furthermore, east-west oriented mountain ranges could also significantly constrain range expansion of species, acting as a barrier to dispersal. Thus, the overall effects of mountains on biodiversity in the face of future climate change seem difficult to predict. However, these effect could be important because they could make distinct trajectories in the spatial reshuffling of species distribution.
The local communities are affected by the species spatial distributions, thus they composition (species and abundances) are affected by the climate change. With the French Breeding Birds Survey database, I analyze the community reshuffling according to the topography through using a functional index, the Community Thermal Index (CTI) which reflects, for a given species assemblage, the balance between low- and high-temperature dwelling species.