Impacts of climate and land-use change on wintering bird populations in Finland

Few studies have covered both the effects of climate and land-use change on animal populations under a single framework. Besides, the scarce multi-species studies conducted have focused on breeding data, and there is little information published on changes in wintering populations. Here, we relate the pattern of long-term temporal trends of wintering bird populations in Finland, north Europe, to covariates associated with climate and land-use change. Finnish wintering populations have been monitored using ca 10 km winter bird census routes (> 420 routes counted annually) during 1959–2012. Population trends of 63 species were related to migratory strategy, urbanity, and thermal niche measured as species-specific centre of gravity of the wintering distribution. Waterbird trends have shown a marked increase compared to landbirds. Among landbirds, forest species have suffered severe declines, whereas urban species have considerably increased in their wintering numbers. To follow up these results, we produced three multi-species indices (for waterbirds, forest and urban species, respectively), which can improve our ability to detect and monitor the specific consequences of climate change and changes in land-use, but at the same time act as a feedback to track the conservation status of the species. Our results suggest that waterbirds are responding to climate change, given their dependence on open water and the correlation with early-winter temperature over the last decades. On the other hand, we believe trends of landbirds have been mainly driven by human-induced land-use changes. While urban species have likely benefited from the increase of supplementary feeding, forest species have probably suffered from the loss of native habitats.