鄱阳湖四种水鸟的栖息地利用与水深和食物的关系

为了了解水深和食物资源对水鸟栖息地利用的影响，2012 ~ 2013年越冬期，采用样方法，对鄱阳湖沙湖的白鹤 (Grus leucogeranus)、小天鹅 (Cygnus columbianus)、东方白鹳 (Ciconia boyciana) 和白琵鹭 (Platalea leucorodia) 4种水鸟的数量、觅食地和休息地的水深以及主要食物——沉水植物冬芽的密度和生物量进行了调查。每个样方为150 m? 150 m的栅格，全湖共设置152个样方。结果显示，10月份沉水植物冬芽的平均水深为 (124.2 ± 12.0) cm。4种水鸟觅食地的水深均显著高于其休息地的水深 (白鹤：Z = 11.96, 小天鹅：Z = 4.69, 东方白鹳：Z = 14.44, 白琵鹭：Z = 29.33, 所有P < 0.01)；对于2种食冬芽的水鸟，白鹤觅食地的水深、冬芽生物量、取食深度以及休息地水深均显著低于小天鹅 (觅食地水深: Z = 8.56, 冬芽生物量: Z = 2.93, 取食深度: Z = 14.69, 休息地水深: Z = 4.34, 所有P < 0.05)，但两者觅食地的冬芽密度差异不显著 (Z = 0.6, P = 0.55)；对于2种食鱼性水鸟，东方白鹳觅食地水深、取食深度和休息地水深均显著大于白琵鹭 (觅食地水深: Z = 10.60; 取食深度: Z = 9.35; 休息地水深: Z = 8.47, 所有P < 0.01)。回归分析表明，白鹤、东方白鹳、白琵鹭的觅食个体数量均与水深呈二次项关系，个体数量最大的觅食地水深分别为23.9 cm，33.0 cm和22.6 cm；白鹤、小天鹅的觅食个体数量均与冬芽生物量呈线性关系。3种涉禽均只能分布在一定的水深范围内，且同种食性的水鸟利用不同的水深从而减少在空间生态位的重叠。

Relationship between Habitat Use of Four Waterbird Species and Water Depth and Food Resource in Poyang Lake

In order to understand the effects of water depth and food resources on the habitat use of waterbirds, we surveyed individual numbers, water depth of foraging and resting sites, food availability (density and biomass of winter buds of submerged macrophytes for bud-feeders) of four waterbird species (Grus leucogeranus, Cygnus columbianus, Ciconia boyciana and Platalea leucorodia) using plot methods in winter 2012 ~ 2013 in Shahu Lake, a sub-lake of Poyang Lake. A total of 152 plots were set in the lake with each plot being 150 m ? 150 m. The buds were collected in October before arrival of waterbirds and waterbirds were counted in January when large amounts of waterbirds concentrated in the lake. Distribution patterns of winter buds in different water depth in October were analyzed using Kolmogorov-Smirnov Z test. We compared water depth between foraging and resting sites of the 4 species using Mann-Whitney U test, respectively. We further compared water depth, density and biomass of winter buds in foraging sites and water depth in resting sites between Grus leucogeranus and Cygnus columbianus (both mainly forage on buds) using Mann-Whitney U test, respectively. We also compared water depth between two piscivorous waterbird species in foraging sites and resting sites, respectively. Regression analysis were used to assess the relationship between foraging bird numbers and water depth for the 4 species, as well as between foraging bird numbers and biomass of winter buds for 2 bud-feeding species. Results indicated that winter buds distributed in an average water depth of (124.2 ± 12.0) cm in October (Fig. 2). Water depth at foraging sites of all the four species were deeper than that at resting sites (Grus leucogeranus: Z = 11.96, Cygnus columbianus: Z = 4.69, Ciconia boyciana: Z = 14.44, Platalea leucorodia: Z = 29.33, P < 0.01 for all) (Table 1). Density of winter buds at foraging sites was not significantly different (Z = 0.6, P = 0.55). For the two bud-feeding waterbird species, Grus leucogeranus roosted in shallower water and foraged in shallower water with lower biomass of winter buds than that of Cygnus columbianus, and the former had shallower 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 resting sites: Z = 4.34, P < 0.05 for all). For the two piscivorous waterbird species, foraging depth, water depth at foraging sites and water depth at resting sites of Ciconia boyciana were deeper 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 < 0.01 for all). Regression analysis indicated significant quadratic relationships between the individual numbers of foraging Grus leucogeranus (R2 = 0.39, P < 0.05), Ciconia boyciana (R2 = 0.31, P < 0.05), Platalea leucorodia (R2 = 0.29, P < 0.05) and water depth at study site (Fig. 3). The water depth with the highest densities of the three species were 23.9, 33.0, and 22.6 cm, respectively. Individual number of foraging Grus leucogeranus (R2 = 0.43, P < 0.01) and Cygnus columbianus (R2 = 0.54, P < 0.05) increased with the increase of biomass of winter buds. Three wader species distributed only within a certain range of water depth and species with same diets distributed at different water depth to reduce overlap of spatial niche.