Common BuzzardsButeo buteoWintering in Eastern Romania: Habitat Use and Climatic Factors Affecting their Abundance

Abstract

The Common Buzzard is a partial migrant in Eastern Europe, but its wintering densities are poorly known for this area due to a low number of studies. However, its migration patterns and wintering grounds can be affected by climate change with local fluctuations in numbers linked to weather conditions. Between 2010 and 2015 we annually carried out 15 transects/winter month in order to count the wintering population of Common Buzzards across Eastern Romania to look for climatic factors explaining variation in wintering density. Transects were controlled during two weeks from the end of the month, each covering a distance of 40 km, outlining the broadest winter monitoring of raptors in Central and Eastern Europe. Road survey was used, with a car driving at a low speed, and two observers counting birds, recording distance and habitat where birds occurred. In analyses, in addition to local weather data also 9 indices integrating weather conditions across longer time windows and larger areas were included. The wintering density calculated for the five-year period was 0.539 individuals/km2 fluctuating during the winter seasons with a possible cyclic pattern. The Buzzards selected pastures and herbaceous vegetation associations for hunting across their wintering grounds. Common Buzzard numbers fluctuate during the winter season (highest in December). They are positively influenced by rising solar flux and negatively by the low North Eastern Europe temperatures and Arctic Oscillation Index recorded within 14 days before the survey, which drive birds to southern wintering areas. These weather conditions (high pressure and low temperatures) represent the onset of the Siberian Anticyclone, a regular, annual weather system that occurs in Eastern Europe every winter.