Carrying Capacity Analysis Of Wintering Hooded Crane (Grus Monacha) At Shengjin Lake

The carrying capacity of wintering waterbirds in the wetlands is very important for scientific management of National Nature Reserve and the protection of species. Hooded crane(Grus monachd) is the large migratory wading waterbirds,IUCN vulnerable species and the national grade I protected birds in China, its distribution depend on wetlands, wintering at Shengjin Lake. But fishery, grazing, road construction makes habitat quality decreased and a substantial reduction in traditional food resources of Vallisneria spiralis and submerged plants, limiting the hooded crane population carrying capacity. The evaluation of the carrying capacity of Shengjin Lake is of great significance for the conservation of species in the degraded wetland.From November in 2014 to April in 2015, the field survey of the foraging activities was carried out by focal animal sampling, statistical hooded crane foraging efficiency, intake rate and feeding success, and we observed the defecation behavior of hooded crane, analysis its daily energy intake and consumption. We use mixed linear model to analysis influence factors of hooded crane foraging behavior, using general linear mixed models to analysis the relationship of feeding efforts and food density, in order to understand the foraging behavior strategies of hooded crane in different wintering stages. Acquisition the remote sensing image during three winter stages to interpretation of habitat type and the area of suitable habitat by the supervised classification using ERDAS and GIS. Food density investigation was carried out to obtain hooded cranes wintering food reserves. Considering the food resources, shelter and settlements, roads and other factors, the wintering hooded crane suitable habitat area of the foraging patches at Shengjin Lake were interpreted and analyzed to calculate suitable habitat area. Based on nutrient carrying capacity formula, considering the hooded crane suitable habitat, habitat utilization rate and the proportion of its population in the same feeding group, overwintering days, daily field metabolic rate and other factors, we calculate the carrying capacity of hooded crane in three wintering stages in different habitat types, and analyze the influential factors.Within the lake area, in the early winter period area of the suitable foraging habitat of hooded crane was 10 km2, including meadows (9.63 km2), mudflats (0.37 km2); in the mid winter period suitable foraging habitat was 14.18km2, including mudflats (9.94 km2), meadows (4.24 km2); in the late winter period suitable foraging habitat was 16.21km2, including meadows (10.56 km2), mudflats (5.65 km2). In the early winter, the food density is high in the meadows (212.200±141.144 g/m2, n=43), lower in the paddy fields (123.395±25.699 g/m2, n=25) and lowest in the mudflats (14.023±5.897 g/m2, n=47). During the middle stage, the food density in the paddy fields decreased significantly (93.206±28.547 g/m2, n=29). The upper lake of Shengjin Lake can provide the total food 3.215×106kg in the early winter period, 2.079×106kg in the middle winter period,2.738×106kg in the late winter period. The suitable habitats can provide energy for 4.306×108kJ in the early winter period, 2.420×108kJ in the middle winter period, and 0.843×108kJ in the late winter period. We calculated the total daily energy intake of hooded crane is 2484.74kJ, according to the winter period is 145 days. At Shengjin Lake the carrying capacity of the hooded crane is 1195 individuals in the early winter period,672 individuals in the midddle winter period,234 individuals in the late winter period.The carrying capacity of hooded crane is mainly affected by the water level and human disturbance in the early winter, when the water level is higher, the suitable habitat area is reduced, and hooded crane will fly to paddy fields to get more food. In the middle winter, hooded crane mainly feeding in the meadows, the carrying capacity is affected by grazing activity. The interference will decrease hooded cranes’energy intake level. In the late winter, hooded crane’s population is mainly limited by food resources quantity, after consumption of wintering waterbirds, food resources are relatively scarce, wintering waterbirds may increase the feeding intensity in order to accumulate energy for them to migrate, bringing habitats greater predation pressure. When food is scarce, hooded crane frequently adjust foraging behavior to wetland degradation and suitable habitat area reduction, and keep a certain energy intake.