The tundra swan (Cygnus columbianus) is listed in the second category of nationally protected wildlife species in China and is regarded as a vulnerable endangered species by the China Red Data Book of Aves. In China, wintering areas include the middle and lower reaches of the Yangtze River and Taiwan among other areas. In recent years tundra swan numbers have decreased in some lakes. The distribution ranges of this species has reduced and it is now concentrated in lakes in Anhui Province and Poyang Lake in Jiangxi Province. Tundra swan inhabit Poyang Lake for approximately 150 days of the year from late October to the middle of March. The wintering ecology of tundra swans was investigated by direct count method in Poyang Lake on five occasions from October 2012 to March 2013. The Poyang Lake National Nature Reserve (PYH), Nanji Wetland National Nature Reserve (NJS), Duchang Migratory-bird Nature Reserve (DC), and the Poyang Baishazhou Nature Reserve (BSZ) were selected to conduct wintering ecology assessments including population dynamics, age structure, and behavior of tundra swans. The results show that tundra swan numbers were not stable at all of the survey sites, indicating that local movement occurs in tundra swan populations. There may be some mechanism by which this local movement is triggered, e.g. food availability or water level. The exact mechanism of local movement requires further study. The tundra swan numbers were highest in the second survey, 10, 756 swans in total. The largest population, 11,199 individuals, was observed in BSZ, accounting for > 56% of total the numbers observed during the experimental period. Temporal variation in the distribution and number of this species was observed in the different lakes of each reserve. However, the species was confined to certain lakes, indicating that only some lakes provide good habitats for this bird. Our results show that the percentage of juveniles was 29.04% (n=1150). The diurnal activity budgets and rhythm of the tundra swan were studied with the instantaneous scan sampling method from December 2012 to March 2013. The birds spent most of their time either motionless (43.12%) or feeding (27.44%), and spent the least amount of time either in motion (16.82%) or cleaning and tidying (11.48%). The motionless behavior peaked between 07:00 and 08:00 h and 17:00 and 18:00 h, whereas, feeding behavior peaked between 16:00 and 17:00 h. The increase in feeding intensity in the afternoon was related to long, cold winter nights. Birds had to acquire enough food and energy to survive through the night. Social behavior differed significantly between adults and juveniles, no differences were found for other behaviors. The diurnal activity budgets and rhythm of adults and juveniles were very different. This difference was mainly observed in their motionless and feeding behaviors. Early research indicates that the tundra swan can forage in deep water areas (about 1 meter), however, none have been observed foraging in grassland. During this investigation we observed many individuals foraging in grasslands and rice fields, which perhaps indicates a lack of food resources in Poyang Lake.