Climate and land use changes: similarity in range and abundance changes of birds in Finland and Great Britain

Climate change and human land use are causing changes to species ranges and abundances. However, factors influencing the species-specific speed and direction of changes are not well understood. In addition, intra-specific variation in the responses has rarely been investigated and thus it is not known if the same species show similar population changes in different areas. We compared the rate of changes in range size (since the 1970s) and population abundance (since the 1980s) as well as shifts in mean weighted latitude of range (since the 1970s) and density (since the 1990s) among the same bird species in Finland and Great Britain, two countries that share similar north– south climatic gradients. Similar responses between countries could indicate that climate change is causing parallel changes in species’ ranges and abundances in the countries. Furthermore, we tested whether the responses differed between habitat types, which could indicate that local habitat availability and land use may be more important than climate change. Wetland species showed parallel range size change in the two countries, but no such connection was found in open and forested habitats. Population abundance trends were also parallel in both countries and northern species showed more negative population trends than southern species. The speed of change in species’ average latitudes was positively correlated between the two countries when using occurrence data, but negatively correlated when using species density. Species that show similar changes in population sizes in Finland and Great Britain, that are likely caused by large scale population drivers, such as climate change. However, speed of latitudinal shifts in species’
densities were not connected between the two countries. These potential differences are likely driven by spatial variation in land use changes and habitat availability.