Abstract
Extensive ephemeral wetlands at Poyang Lake, created by dramatic seasonal changes in water level, constitute the main wintering site for migratory Anatidae in China. Reductions in wetland area during the last 15 years have led to proposals to build a Poyang Dam to retain high winter water levels within the lake. Changing the natural hydrological system will affect waterbirds dependent on water level changes for food availability and accessibility. We tracked two goose species with different feeding behaviors (greater white‐fronted geese Anser albifrons [grazing species] and swan geese Anser cygnoides [tuber‐feeding species]) during two winters with contrasting water levels (continuous recession in 2015; sustained high water in 2016, similar to those predicted post‐Poyang Dam), investigating the effects of water level change on their habitat selection based on vegetation and elevation. In 2015, white‐fronted geese extensively exploited sequentially created mudflats, feeding on short nutritious graminoid swards, while swan geese excavated substrates along the water edge for tubers. This critical dynamic ecotone successively exposes subaquatic food and supports early‐stage graminoid growth during water level recession. During sustained high water levels in 2016, both species selected mudflats, but also to a greater degree of habitats with longer established seasonal graminoid swards because access to tubers and new graminoid growth was restricted under high‐water conditions. Longer established graminoid swards offer less energetically profitable forage for both species. Substantial reduction in suitable habitat and confinement to less profitable forage by higher water levels is likely to reduce the ability of geese to accumulate sufficient fat stores for migration, with potential carryover effects on subsequent survival and reproduction. Our results suggest that high water levels in Poyang Lake should be retained during summer, but permitted to gradually recede, exposing new areas throughout winter to provide access for waterbirds from all feeding guilds.
Highlights
The extensive and numerous ephemeral wetlands of the Yangtze River floodplain (YRf) are ecologically and economically important
Our results suggest that high water levels in Poyang Lake should be retained during summer, but permitted to gradually recede, exposing new areas throughout winter to provide access for waterbirds from all feeding guilds
Twenty-nine waterbird species occur in numbers exceeding 1% of their global population, including almost all of the world’s population of Siberian cranes Grus leucogetanus, oriental storks Ciconia boyciana, and swan geese Anser cygnoides (Ji et al, 2007)
Summary
The extensive and numerous ephemeral wetlands of the Yangtze River floodplain (YRf) are ecologically and economically important. Delayed flooding shortens the macrophyte growing period, reducing biomass (Cao et al, 2011; Wang, Lee, & Cheng, 2005; Zhang et al, 2011), and may result in declining numbers of waterbirds as already shown in major river basins in Australia (Kingsford, 2000; Kingsford, Bino, & Porter, 2017; Kingsford & Thomas, 2004) Because of these predicted consequences of Poyang Dam on waterbirds, we investigated the current changes in spatial distributions of two goose species in the lake in relation to the availability of their contrasting food resources. Swan geese were formerly abundant throughout the YRf but are confined to Poyang Lake due to the loss of submerged macrophytes, mainly Vallisneria spp., throughout the YRf (Fang et al, 2006; Fox et al, 2011; Jia et al, 2016; Zhang et al, 2011). Our study will provide information on the likely responses of waterbirds to the construction of the proposed Poyang Dam and will contribute to making knowledge-based conservation decisions on the management of future water levels
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