Effects of Vegetative Cover Changes on the Carrying Capacity of Migratory Shorebirds in a Newly Formed Wetland, Yangtze River Estuary, China

Zhen-Ming Ge ； Xiao Zhou ； Tian-Hou Wang ； Kai-Yun Wang ； Enle Pei ； Xiao Yuan

《Zoological Studies》 48卷6期 (2009/11) Pp. 769-779

並列摘要

The Jiuduansha wetland is a shoal which formed in the Yangtze River estuary during the 1940s. Shorebird surveys were conducted at Jiuduansha wetland in 2004-2005 during the spring (northerly) and autumn (southerly) migration seasons. Over 6000 individuals of 25 shorebird species were recorded at the wetland during spring and 3000 birds during autumn. Their preferred roosting habitat was the bare mudflat and bulrush (Scirpus × mariqueter and S. triqueter) zones. The carrying capacity of the wetland for shorebirds based on the available foraging resources of medium-sized macrobenthos was estimated during the spring and autumn of 2006. Thirty species of macrobenthos were identified and defined as potentially appropriate food for shorebirds at Jiuduansha, comprised mostly of mollusks, crustaceans, and annelids (polychaetes). The total standing benthic invertebrate crop was 1973.64 kg ash free dry weight (AFDW) in spring and 1557.28 kg AFDW in autumn. We calculated that this could theoretically support about 1.51×10^6 bird-days (the number of birds present) in spring and 1.20×10^6 bird-days in autumn. However, field surveys in 2006 indicated that only 10% of the standing crop of biomass was available to shorebirds, and that the actual carrying capacities were about (0.15 and 0.12) × 106 bird-days in spring and autumn, respectively. Actual shorebird abundances at Jiuduansha were significantly lower than the theoretical carrying capacity. Furthermore, satellite imagery from 1998-2006 indicated that an introduced species of smooth cordgrass Spartina alterniflora has rapidly spread, invading the bare mudflat and bulrush zones. This has reduced the availability of suitable high-tide roosting habitat, and may be the key factor, rather than food availability, limiting use of the area by shorebirds. We provide recommendations for the management of Jiuduansha wetland to benefit shorebirds and other waterbird species.

並列關鍵字

Recently formed wetland ； Shorebirds ； Macrobenthos ； Change in vegetative cover ； Spartina alterniflora