关键词: 树木年轮学, 生长历史, 古树, 树龄

Abstract: To establish baseline information about the spring migration of waterbirds, we conducted surveys on the current status and habitats of whooper swans (Cygnus cygnus) and other waterbirds along the upper and middle reaches of the Yellow River in Inner Mongolia, ranging from Dengkou County to Tumed Right Banner based on distributions of vegetation types and the river stream in March 2015 and April 2016. Day and night home ranges for tracking whooper swans were determined using kernel density estimation (KDE) at levels of 90% and 50%. Enhanced vegetation index (EVI) of these two levels were calculated and compared. A total of 25671 waterbirds were recorded, belonging to 37 species, of which swans and ducks accounted for 89.6%. The whooper and tundra swan (C. columbianus) were predominant. According to GPStracking data, the upper and middle reaches of Yellow River were important stopover sites for spring migratory whooper swans, where the most swans stayed for long periods ((24.74±9.38) d). Their diurnal and night movements were roughly similar. The EVI at the upper and middle reaches of Yellow River were very low. Compared with that of the 90% level of KDE, the home range size of the 50% level and corresponding EVI were much lower from Dengkou County to Tumed Right Banner. During our field surveys, we discovered that these stopover sites were located on farmland around the Yellow River, providing abundant food and better shelter habitats for whooper swans and other waterbirds.

Key words: tree age, old tree, growth history, dendrochronology