Impact Of Water Level Fluctuation On Siberian Crane And Other Wintering Waterbirds In Poyang Lake

Hydrologic process and its impact on wetland has always been one of the hot issues in ecological studies, which is crucial for understanding the relationship between ecological processes, ecological components and ecosystem services. Poyang Lake is one of the most important wintering grounds for migrating waterbirds in China. Over14endangered waterbird species wintering there. In addition, wintering population of27waterbird species exceeds1%of their global populations, amongst which, more than98%of the Critically Endangered Siberian cranes’(Grus leucogeranus) global population wintering here. Since the operation of the Three Gorges Dam, downstream rivers and lakes have been significantly affected, which become a great concern from conservation societies. The key issue concerned is the impact of water level on migrating birds and their habitats. Thus, assessing the impacts of water level on wintering birds and their adaptability to environmental changes are the most urgent task for Poyang Lake wetland protection. This dissertation collected and reviewed bird census data in the Poyang Lake area from1998to2013,identified key ecological characters of the Poyang Lake wetlands, vegetation and waterbirds, and established a coupling model that can project the relationship between water level, habitat and wintering waterbirds. Further studies focus on impact of water level fluctuation on food resources of the birds, and the responses of the birds to the environmental change, in particular, the Siberian cranes. The study revealed following findings:1. Water level fluctuation scale defines differentiated impacts on various habitats and food resources. For all water bird groups, the lowest accept water level range for waterbirds is between8.2and8.8m above sea level in winter, whereas the highest accept water level in summer17.4m above sea level. The lower limit water levels for the five foraging bird groups (Tuber feeders, Sedge foragers, Seed eaters, Invertebrate eaters and Fish eaters) in winter are>8.5m;>8.3m;7.2-8.4m;<8.8m;<8.4m respectively, and in summer are-;-;<17.6m;<17.4m; and<17.4m, respectively. The highest water level does not affect the first and the second diet group. For Siberian cranes, the optimal water level is between8.7-10.2m in winter and no higher than19.5m in summer.2. Based on the1983-2012population data of the wintering Siberian cranes in the Poyang Lake National Nature Reserve and related environmental data, this study builds a GAM model for Siberian cranes and revealed that the population growth rate for Siberian cranes has been4.08%per year over the past30years, with the total population grows from840in the1983-1984winter, to4315in the2011-2012winter.3. Adverse water level may significantly reduce the tuber density of V. spiralis that Siberian cranes mainly forage on. The tuber density of V. spiralis at Benghu Lake and Dahuchi Lake was1.24per m2and0.17per m2in Jan.,2011. The numbers of V. spiralis seedlings and sprouts was18.2±13.6and38.6±38.8, May2011and May2012, which was significantly difference in the two years (p<0.001). The nutrition contained in the tuber of V. spiralis, main root of P. limprichtii and Amana edulis that Siberian cranes foraged on varies considerably, but nutrition had no significant impact on the food choice for Siberian cranes.4. In2010, due to extreme low density of V. spiralis tubers, Siberian cranes shifted their habitat from shallow water area to grassland, and were found to feed the roots of P. limprichtii instead of V. spiralis tubers. Observation shown their overwintering behaviors changed significantly (p=0.008), compared to their behaviors in shallow water, where they normally forage. Their foraging time is shorter (p=0.00), while the alerting time is significantly increased (p=0.00). In2011, when water level fluctuate within the normal range, almost all Siberian cranes foraged at their normal habitat (shallow water and mudflats) spend more time foraging and less alerting on mudflats. This indicates that Siberian cranes choose the optimal habitats in normal years and survive bad conditions by changing their habits, which conforms to the Optimal Foraging theory.The upper and lower water level limits for the waterbirds suggested in this dissertation are important for the protection of Siberian cranes and other waterbird species. The GAM Model result shows that extreme high water level has significant negative impact on populations. The water levels of Yangtze River and Poyang Lake Inflow Rivers controls water level of the Poyang Lake. The operation of the Three Gorges Dam forges a potential threat to the wintering birds in this area. This study provided a reference for the proposed Poyang Lake Dam and its operation. The study also demonstrates that Siberian cranes prefer optimal habitats though they are able to adapt themselves to a new environment.In conclusion, this dissertation developed a model that builds on the long-term bird census data to analyze the relationship between water birds and water level in Poyang Lake, and revealed acceptable water levels for five different foraging groups and Siberian cranes in winter and summer, and verifies the optimal foraging theory of Siberian crane’s habitat selection, which advanced our knowledge in the field.