Effects of tidewater on the feeding ecology of hooded crane (Grus monacha) and conservation of their wintering habitats at Chongming Dongtan, China

摘要

Dongtan (or East Tideland) on Chongming Island in China is an important wintering site of Grus monacha (hooded crane). Field observations were conducted in Dongtan in the wintering season of 2000-2001 to determine how tidal fluctuation affects the habitat use and behavior of G. monacha. Scirpus mariqueter (sea-bulrush) was the dominant species in the tidal vegetation; and its corms were the major food source for G. monacha. The corms in the outer zone (far from the dyke) were buried underground shallower than those in the inner zone (near the dyke) because of erosion by tidewater. For easy access to food, G. monacha tended to select the outer zone and the edge of tidal creeks as its foraging sites for the majority of time spent on the tideland. Regression analysis revealed that distance of the foraging sites to the dyke was correlated with tidal height. The cranes did not appear to show territorial behavior, and tended to form large-sized flocks, especially at high tide, because of the effect of the tidewater and the non-uniform distribution of food. Thus, the height of the tide is an important factor responsible for the habitat selection of G. monacha, which was also the major cause of the cranes selecting only the natural tideland at Dongtan on Chongming Island. Unfortunately, the habitats of G. monacha are limited, and even threatened, at Dongtan because the tideland is frequently reclaimed. Appropriate measures should be taken to prevent the tideland being further reclaimed, otherwise the natural wintering grounds of G. monacha will soon disappear.