Carrying Capacity of Red-crowned Cranes in the National Yancheng Nature Reserve, Jiangsu, China

Abstract

The coastal-zone wetland in Yancheng, Jiangsu Province is the largest winter habitat of the Red-crowned Crane (Grus japonensis) in the world. The essential research question addressed in this paper is: What is the carrying capacity for Red-crowned Cranes in this habitat? Since water is ample in the salt marsh, the two vital limiting factors for the crane habitat are food and shelter. In this study, based upon crane numbers and their distribution during the winter of 2004-2005, the authors adopt the “Neu technique” to analyze habitat selection of Red-crowned Cranes to 8 types of tidal flat environments in the Yancheng Nature Reserve. Applying the “heat quantity method”, we find corn feed distributed by the nature reserve staff cannot support survival of wild cranes. Subsequently, using the “gravimetric method”, with the crane utilization of each habitat as a weighting, we estimate that total food supply in the nature reserve is far greater than required by the crane population in one winter season. This indicates that food supply is not a determining factor for this particular habitat selection. Moreover, from analysis of food selectivity it is evident that the preferred food comprises vegetal paddy chaff and supplemental corn feed, with natural vegetation occupying only a small proportion of their total food consumption. The spatial distribution of cranes was between 0.8-2.5 individuals per km2, so that an optimum habitat of 1000 km2 may contain 800-2500 cranes. Observations from the present study show that preferred spatial location has shrunk in the past 10 years toward a core area surrounded by a buffer area (641 km2 in all), so that potentially the entire nature reserve could support ~570-2000 cranes. In addition, some 500 cranes are contained within an artificial waterfowl lake. In total it appears that the carrying capacity of the Yancheng Nature Reserve is of order 2500-3000 cranes, and they prefer to roost in a coastal habitat of lower salinity where food supply is plentiful, and which is distant from human disturbance.