Stopover Ecology Of Shorebirds In Chongming Dongtan, Shanghai

Shorebirds (Charadriiformes) are typical waterbirds wading in inland and coastal wetlands. It is a conspicuous birds aggregation in wetlands for its multi-species and great abundance. Shorebirds concentrate on large estuaries, bays, coastal area and inland wetlands. At these stopover sites, a large number of shorebirds species with similar requirements come together forming dense multi-specific aggregations in relatively uniform limited habitats. Stopover sites along the flyway are vital for shorebirds to refuel and finish their migration to the breeding ground. Chongming Dongtan, a wetlands of international significance, is an important stopover site for shorebirds in the East Asian-Australasian Flyway (EAAF), it is also the first important stopover site of the south of Yellow Sea area supporting the migration of at least 250 thousands of shorebirds. To study the role of Chongming Dongtan on supporting the migration of shorebirds and provide scientific data to shorebirds conservation, focusing on food resources of shorebirds that Chongming Dongtan wetlands provided and how shorebirds used it, this project has sampled the macroinvertebrates and surveyed the distribution of shorebirds in the intertidal area of Chongming Dongtan attempting to discern the spatio-temporal dynamics of macrobenthos and shorebirds, foraging strategy related habitat use, and the relationship of different environmental factors with the great difference of shorebirds abundance during the northward and southward migration. The main results were as follows:1. With core samples, macrobenthos as shorebirds preys were found at high densities in Scirpus salt marshes. Macrobenthos distributed mainly in the upper 3 cm substrate. Gastropods and bivalves were the two main categories of macrobenthos, but there were different in distribution. Distribution of macrobenthos had an important influence on shorebirds distribution. Thirty-five species of macroinvertebrate including 9 species of gastropods, 5 of bivalves, 6 of polychaetes, 2 of oligochaetes, 11 of crustacean, and 2 species of insect larvae were recorded. There was significant difference in density of total and different categories of macrobenthos along the intertidal altitudinal gradient. Higher density of total macrobenthos and gastropods occurred in Scirpus salt marshes zones, conversely, bivalves mainly distributed in zones from IS to SF. Eighty percent of the total abundance of macroinvertebrates was detected in the upper 3 cmsubstrate, densities of macrobenthos decreased as the buried depth increased. Except for significant low density in July, there was no significant difference in macroinvertebrates density among the seasons. Assiminea violacea, Stenothyra toucheana and Corbicula flumicea, and Ilyoplax deschampsi were the main preys of shorebirds.2. Spatio-temporal patters of shorebirds were studied in Chongming Dongtan intertidal area. It was found that different categories of shorebirds and congeners overlapped to some extent in spatial distribution and migration time. They shared the intertidal area mainly by partial separation in habitats for different categories of shorebirds or in migration time for congeners. The study showed that Shorebirds mainly distributed in the salt marshes fringe and bare flats. Peaks densities of plovers and calidrid sandpipers overlapped in migration time, but shared the intertidal area of Chongming Dongtan through partial separation of space. No significant difference was observed in densities and species richness of Curlews and Tringid Sandpipers. Peak densities and species richness were found in the later stage and both were 15-20 days later than Plovers and Calidrid Sandpipers. Most of the congeners overlapped in space, whereas they staggered in migratory time. The two most abundant species, Great Knots and Dunlins, coexisted through spatial separation.3. Combined the distribution of shorebirds in the intertidal altitudinal gradient and foraging strategy integrating birds prey sensory mechanism and locomotion, this study suggested that foraging strategy play an important role in shorebird habitat use. This study showed there were significant difference of macrobenthos and different categories of macrobenthos densities in shorebirds habitats. Over 90% of macrobenthos were found in the upper 3 cm substrate. Proportion of epifaunal life form macrobenthos in salt marshes were much higher than that of the bare flat, the opposite trend occurred in infaunal life form, nearly equal proportions in the transition of salt marsh and bare flat. Different foraging strategy shorebirds also showed different habitat use. Pause-travel shorebirds mainly utilized salt marshes fringe, tactile continuous shorebirds relied heavily on bare flats. There was no significant difference in habitats use for visual continuous shorebirds. High percentages of tactile shorebirds occurred in bare flats, while high proportion of visual continuous in salt marshes. Tactile continuous shorebirds were found to positive correlate to bivalve density and visual continuous to crustaceansignificantly. Pause-travel foraging strategy shorebirds were correlated positive to epifaunal and negative to infaunal life form macrobenthos significantly, whereas tactile foraging strategy positive to infaunal and negative to epifaunal life forms. Foraging strategy might play an important role in shorebirds habitat use in the intertidal areas.4. By comparison of habitat use of shorebirds, macrobenthos in intertidal area, vegetation, and tide level of both northward and southward migration periods, the differences of environments were found to influence the optimal migration strategy selection of shorebirds in different migration periods, and new evidence were put out to explain the differences of abundance in southward and northward migration. The study showed that species numbers recorded in both migrations periods were almost no difference, but species richness and abundance in different habitats exhibited significant difference. There was great difference in main habitats use of shorebirds between northward and southward migration. No significant differences were found in macrobenthos density and species richness for the northward and southward migration. Of the four main prey species of shorebirds, densities of Stenothyra toucheana and Corbicula flumicea in autumn were significant higher than that in spring, whereas no significant differences were found in Assiminea violacea and Ilyoplax deschampsi. Whether vegetation height and coverage or high tidewater and low tidewater level, it is high in autumn than that in spring. This makes the main habitat that shorebirds utilized in spring unavailable in autumn. Juveniles comprised over 80% of the birds population. Comparison of environments during northward and southward migration periods showed that the unavailability in southward migration of the main habitats that shorebirds used during the northward migration may be the reason of great difference of abundance between northward and southward migration.