江苏盐城国家级珍禽自然保护区丹顶鹤的承载力

Carrying capacity of red-crowned cranes in the national Yancheng rare birds Nature Reserve,Jiangsu Province,China

江苏盐城沿海滩涂地区是世界上最大的丹顶鹤(Grus japonensis)越冬地.如今全球的丹顶鹤仅约2700只,而每年在此越冬的丹顶鹤接近世界野生个体总数的一半.因此,盐城滩涂的环境状况对于保护该物种的意义不言而喻.该地区能够容纳承养多少丹顶鹤?这是一个关键性的问题.此前尚无人就盐城滩涂对丹顶鹤的承载力作过详细分析.处于保护下的野生动物应按照'生态承载力'来分析其容纳量.由于滩涂上水源较充足,食物和隐蔽物就是丹顶鹤对生境的主要两方面需求,也即限制因子.根据2004～2005年越冬期统计的鹤数及其分布,运用Neu方法分析丹顶鹤对盐城8种不同栖息地的选择性,结果显示它们最偏爱的生境是稻田和草滩,可以栖息在芦苇(Phragmites commums)地、淡水养殖塘或大米草滩,而回避的生境是泥滩、盐田、盐地碱蓬(Suaeda salsa)滩.之后,作者用'热量法'计算了射阳基地圈养丹顶鹤的饲料成分,基本符合营养定额标准;而人工投放的玉米饲料难以保障野生鹤的生存.又按'重量法',以丹顶鹤对各生境的利用程度为权重,估算得盐城保护区可利用的食物总量远远大于鹤群一个越冬期所需量,表明食物并非生境的决定性因子.此外,作者分析了丹顶鹤对各种主要食物的选择性,发现植物在食物总量中占比例极小,但其喜爱的食物却是植物性的稻谷和人工的玉米饲料.总而言之,其种群喜爱居留在淤长型海岸带及食物量大、距道路(人类活动)远、盐度小的栖息地.核心生境丹顶鹤的分布密度约0.8～2.5只/km2,则1000km2最适宜生境的容纳量为800～2500只;实际上,近10a来80%～90%的鹤群分布收缩在核心区与缓冲区(面积共641km2),则整个保护区容纳量为570～2004只.结合这两方面考虑,作者预测盐城保护区的丹顶鹤承载力为2000～2500只,目前其数量未达饱和,种群还将增长.

The coastal-zone wetland in Yancheng, Jiangsu Province is the largest winter habitat of the Red-crowned Crane （Grus japonensis） in the world. At present, about 2700 Red-crowned Cranes live over the globe. Each year, nearly half of the Redcrowned Crane population fly to Yancheng to spend the winter. Accordingly, the environmental condition of the wetland for protection of this species is of highest significance. The essential question is.. How many Cranes can be accommodated there？ The carrying capacity of this habitat for the Red-crowned Crane has not previously been studied. Protected wildlife may be analyzed according to the protocol of ＂ecological carrying capacity＂. Since water is ample in the salt marsh, the two vital limiting factors for the Crane habitat are food and shelter. In this statistical study, based on Crane numbers and their distribution during winter of 2004~2005, the authors adopt the ＂Neu technique＂ to analyze habitat selection of Red-crowned Cranes to 8 kinds of tidal flats in Yancheng. The results reveal （i） that the Cranes preferentially select paddy fields and grasslands; （ii） they are less likely to inhabit reed beds, aquiculture ponds and Common Cordgrass （Spartina anglica） fields; and （iii） they tend to avoid mud flats, salt fields and Saline Seepweed （Suaeda salsa） flats. Subsequently, applying the ＂heat quantity method＂, we calculate nutrient content in foodstuff ingredients of Cranes fed at Sheyang Base, and discover that nutrition achieves quota level in the main; but corn feed distributed by the staff cannot support survival of wild Cranes. Then using the ＂gravimetric method＂, with the Crane utilization of each habitat as weighting, we estimate that total food supply in the Nature Reserve is far greater than required by the Crane population in one wintering season. This indicates that food supply is not a determinant factor for this habitat selection. Moreover, by analysis of food selectivity of the Cranes, we find their favorite foods are vegetal paddy chaff and artificial corn feed, with natural vegetation occupying only a small proportion of their total food consumption. The spatial distribution of Cranes is between 0.8-2.5 individuals per km^2, so that an optimum habitat of 1000 km^2 may contain 800-2500 Cranes. Actually Crane distribution has shrunk toward a core area and buffer area in the past 10 years （641km^2 in all）, so the entire Nature Reserve could support 570-2004 Cranes. In overview we predict that the carrying capacity of the Yancheng Nature Reserve is 2000- 2500 Red-crowned Cranes. Their present population has not achieved saturation capacity and has the potential to increase in the future. In summary, it appears that Red-crowned Cranes prefer to roost in a coastal habitat of lower salinity where food supply is plentiful, and which is distant from human disturbance.