Recent climate change has increased forest winter bird densities in East Europe

Abstract

Recent studies on climate change have reported serious impacts on winter forest birds in Western Europe. However, in areas where climate change has caused milder winters and more stable conditions in summer, one would expect resident bird populations to increase, rather than to decrease in winter. The aim of this study was to investigate the impact of climate change on the population dynamics of ten species of Passeriformes in the Tartarstan Republic, Russia. Ravkin’s transect method was used to census fixed randomly selected plots spread over a large geographic area at least once every month for the past 26 years. Observers remained the same over the whole period. The abundance of nine species in the first half of the winter and four species in the second half of the winter showed significant increases during the study period. Unlike studies from countries in Western Europe, there were no significant decreases in these species. Significant changes in winter conditions, as well as during the breeding season, and an overall increase in annual temperatures are likely reasons for a significant increase in the number of birds in winter. Greater winter survival, an increase in the survival rate of fledglings and juveniles during the summer, and later onset of winter, are very important determinants of the winter population. Our findings show that numbers of birds in late winter are related to the severity of winter conditions. Our data do not support conclusions that the populations of forest bird species have decreased due to climate change.