Poyang Lake Ecology Study

The Poyang Lake Basin in Jiangxi Province is one of the most important wintering areas for migratory waterbirds in Asia, with 98% percent of the global population of Siberian Cranes, 50% of White-naped Cranes, 50% of Swan Geese, and tens of thousands of egrets, spoonbills, storks, swans, geese, ducks, and shorebirds wintering at the site. The population and distribution of Siberian Cranes, as well as other waterbirds within the Poyang Lake Basin, are affected by food resources. These food resources are affected by how clear the water is, how much water is present during the growing cycle, and the timing of water fluctuations in the lake basin. Since 1998, ICF has been working with the Poyang Lake Nature Reserve (PLNR) on a study of the relationships among water levels, cranes, and their aquatic food plants. Through the last ten years, we have collected data and sampled vegetation, tubers, water levels and water quality, and crane habitat use. These research efforts have identified several significant trends within the reserve. Primary among these is the recognition of the role that winter water levels play on Siberian Cranes accessing the tubers of Vallisneria. Vallisneria is an essential food source for the wintering cranes, Swan Geese, and other waterbirds, yet within the four sample lakes we have been studying, locations of Siberian Cranes do not correlate well with tuber densities in the mud. This result contrasts with the Tundra Swans, which also feed on Vallisneria, where locations of the swans do correlate with Vallisneria tuber distribution. The swans, however, are able to feed in greater depths of water because of their long necks and their habit of treading their feet rapidly up and down, stirring up the bottom mud to expose buried tubers. Siberian Cranes, on the other hand, feed where there are high tuber densities and where shallow water allows them to dig. The cranes primarily use depths < 30 cm although they appear to sometimes use water as deep as 50 cm. Regardless of how many tubers may be present within a lake, Siberian Cranes do not use areas with water levels above 50cm, and will seek other areas to feed. Now ICF and PLNR are proposing habitat selection models for Siberian Cranes that can be applied across PLNR and to other areas of Poyang Lake, attempting to predict where suitable Siberian Cranes habitat may be. This method can be used for other bird species as well. Higher water levels in winter would significantly reduce potential foraging areas. This research, together with related studies by others concerning hydrology, land use, and light availability for Vallisneria, is helping the Chinese Government understand what the Siberian Crane and other waterbirds need to survive during the winter months at Poyang. This knowledge is helping to evaluate the implications of developments now being considered within the lake, including a variety of water-control projects that could drastically alter the hydrology of the system. Additionally, these data are also illustrating previously unsuspected impacts of new aquaculture practices within PLNR.