Communty Characteristics And Habitat Use Of Waterbirds In Shahu Lake Of Poyang Lake National Nature Reserve

Poyang Lake National Nature Reserve is located in the northwest of PoyangLake, the largest freshwater lake in China. It is important wintering grounds forwaterbirds in the East Asian-Australasian Flyway. Shahu Lake is a typical shallowdish lake in the reserve, which provides suitable habitats and abundant food forwaterbirds. This study analyzed spatial characteristics of wintering waterbirdcommunity in Shahu Lake. Using plotmethod, I analyzed the species, density,biomass, distribution, and their contribution to herbivorous waterbirds of winter budsof submerged plants, the main food for herbivorous waterfowls in Shahu Lake.Habitat use of four common natioanl key portected waterbirds, Grus leucogeranus,Cygnus columbianus, Ciconia boyciana, and Platalea leucorodia, was studied andtheir influencing factors were further discussed. This study provides scientific basisfor the protection of waterbirds and their habitats. The main results were listed asfollows:1. Wintering waterbird community in Shahu LakeA total of26waterbird species and11063individuals in15genuses,11families,and6orders were recorded. Both the species and individual numbers of Anseriformesare dominant. The average density of waterbirds was2.63ind/hm2in Shahu Lake.Comparison on the species number and density among various habitats indicated thatthe shallow water habitat supported the highest number of waterbird species, foragingspecies, individual density of foraging species, and the proportion of foraging speciesnumber. Deep water habitat supported the highest waterbird density. Mudflat habitatsupported the highest proportion of foraging species density. Both the speciesdiversity and the evenness index were significantly different among various habitats.The species diversity index decreaed from shallow water (2.12±0.03), mudflat (1.780.09), deep water (1.78±0.09), to the meadow (1.14±0.12) habitats. The evennessindex decreaed from mudflat (0.88±0.08), shallow water (0.86±0.05), deep water(0.8±0.04), to meadow (0.62±0.04) habitats. For the community similarity, mudflatand shallow water habitats had the highest similarity (0.69), and mudflat and deepwater habitats had the lowest similarity (<0.01).2. Distribution of winter buds of submerged macrophytes and their contribution toherbivorous waterbirds Winter buds of two submerged plant species, Vallisneria spinulosa and Hydrillaverticillata var. rosburghii, were recorded. The average density of winter buds ofVallisneria spinulosa was (9.53±1.73) ind/m2and of Hydrilla verticillata var.rosburghii (25.78±3.97) ind/m2in October, which were significantly higher than thatin April ((2.52±0.91) ind/m2for Vallisneria spinulosa and (4.76±1.17) ind/m2forHydrilla verticillata var. rosburghii)(Z=3.712, P <0.01and Z=5.738, P <0.01,respectively). The average biomass of winter buds (dry weight) of Vallisneriaspinulosa was (3.070.65) g/m2and of Hydrilla verticillata var. rosburghii (5.430.75) g/m2in October, which were significantly higher than that in April ((0.890.35)g/m2and (2.210.59) g/m2, respectively)(Z=3.118, P <0.01; Z=3.821, P <0.01).The density of Hydrilla verticillata var. rosburghii winter buds was significantlyhigher than Vallisneria spinulosa winter buds in October (Z=3.466, P <0.01) whilethere was no significant difference in the density of the two species of winter buds inApril (Z=1.677, P=0.09). The average depth that suitable for the formation ofwinter buds of the two species of submerged plants was (2.630.15) m and (2.610.12) m, respectively, in flooding season (from April to September). Winter buds ofVallisneria spinulosa and Hydrilla verticillata var. rosburghii are important food forherbivorous waterbirds in Shahu Lake. It is estimated that waterfowl consumed1.04108ind (1.9104kg) of the two species of winter buds in winter.3. Habitat use of four waterbird species and their relationship to water depth and foodNon-parametric tests indicated that water depth at foraging sites of all the fourspecies were deeper than that at resting sites (Grus leucogeranus: Z=11.96, Cygnuscolumbianus: Z=4.69, Ciconia boyciana: Z=14.44, Platalea leucorodia: Z=29.33,P <0.01for all). Density of winter buds at foraging sites was not significantlydifferent among species (Z=0.6, P=0.55). For the two bud-feed waterbirds, Grusleucogeranus roosted in shallower water and foraged in shallower water with lowerbiomass of winter buds than that of Cygnus columbianus, and the former hadshallower foraging depth that the latter (water depth at foraging sites: Z=8.56;biomass of winter buds: Z=2.93, foraging depth: Z=14.69, water depth at restingsites: Z=4.34, P <0.05for all). For the two piscivorous waterbirds, foraging depth,water depth at foraging sites and water depth at resting sites of Ciconia boyciana weredeeper than that of Platalea leucorodia (water depth at foraging sites: Z=10.60,foraging depth: Z=9.35, water depth at resting sites: Z=8.47, P <0.01for all).Regression analysis indicated significant quadratic relationships between the individual number of foraging of Grus leucogeranus, Ciconia boyciana, Platalealeucorodia, and water depth at study site, repectively. The water depth with thehighest densities of the three species was23.9,33.0, and22.6cm, respectively.Individual numbers of foraging Grus leucogeranus and Cygnus columbianusincreased with the increase of biomass of winter buds. Three wader speciesdistributed only within a certain range of water depth and species with same dietsdistributed at different water depth, which might be to reduce overlap of spatial niche.