Rapid climate change has increased post‐breeding and autumn bird density at the eastern limit of Europe

Abstract

AbstractWe investigated how the densities of birds in the post‐breeding and autumn phase (hereafter called autumn) were changing and how they were influenced by a changing climate in a study region that experienced about 5 months of snow cover each winter and summer temperatures that varied greatly from year to year. Bird densities during autumn were estimated between 1991 and 2018 using distance sampling along transects. Densities were compared to various temperature variables in preceding months and to densities in the following winter. The study region has experienced rapid temperature change in May–August, and autumn densities of six of the nine studied species increased significantly during the study period. Autumn densities of all but one bird species were significantly related to one or more of the temperatures in the preceding January–February, affecting adult survival, and in the preceding May–August, affecting nestling survival. Long‐term trends of autumn densities and densities in the first half of winter were similar for practically all bird species. The results of our study of seasonal dynamics based on eight‐month intervals in each of the 28 years of research emphasize that understanding the influence of climatic parameters on changes in the density of individual bird species requires such long‐term monitoring throughout the year. In a period of climate warming, and in spite of the severity of the winter and the variability of summer, we found that most species of birds showed a clear increase in density.