Declines in the tuber‐feeding waterbird guild at Shengjin Lake National Nature Reserve, China – a barometer of submerged macrophyte collapse

Abstract

ABSTRACT1. The Yangtze floodplain is globally unique for its extensive ephemeral wetlands, recharged by summer monsoon precipitation. The annual cycle of inundation and water table recession favours submerged macrophytes, including Vallisneria that overwinters in desiccated substrates as tubers, which provide highenergy winter food for tuber-feeding waterbirds that were formerly abundant in the region. 5. Widespread declines and concentration of tuber-eating wintering waterbirds at other sites elsewhere in the Yangtze floodplain may also reflect the local collapse of submerged macrophytes and of ecosystem services that these wetlands provide to the human communities.

Effects of shading onVallisneria natans(Lour.) H. Hara growth

“…at Shengjin Lake declined greatly in recent years, especially in the Upper Lake in areas covered since 2007 with Trapa spp. (see map in Fox et al, 2011). In 1974, the whole lake was covered by the submerged macrophytes Vallisneria spp.…”

“…at seasonally inundated Yangtze River floodplain wetlands could have contributed to reductions in annual biomass production and seed production of this important submerged macrophyte and contributed to declines in its distribution and abundance. Such changes have had important knock-on effects for the waterbird and fish communities of such lakes (see for example Fox et al 2011 andZhang et al 2011) and doubtless had other trophic effects through these aquatic systems. However, proof that Trapa spp.…”

“…Yan, have been cited as the cause of major declines in wintering numbers of Swan Geese Anser cygnoides L., Tundra Swans Cygnus columbianus bewickii Yarrell and other tuber-feeding birds Fox et al, 2011). The causes of general declines in Vallisneria spp.…”

Philopatry in a changing world: response of pink-footed geese Anser brachyrhynchus to the loss of a key autumn staging area due to restoration of Filsø Lake, Denmark

“…The switch to an agricultural diet characteristic of both this population (Fox et al 2005) and other species of geese (Rosin et al 2012) opened the door to an almost inexhaustible food resource in the Danish landscape, and the availability of staging sites during the autumn migration may therefore depend more strongly on the relative proximity of secure roosting areas rather than specific food resources. As a consequence, philopatric waterfowl species exploiting cultivated areas might be much less susceptible to changes in staging areas than species targeting specific food sources much less available in a modern landscape (Clausen et al 2012;Fox et al 2011;Wang et al 2012). …”

“…As a consequence, species with restricted habitat choice and few available areas may suffer to a greater extent than species with flexible food choice and a selection of many and/or abundant habitats (Clausen et al 2012;Fox et al 2011). The ability of migrating birds to alter site use and migration patterns in response to habitat loss at stopover sites is dependent on the behavioral flexibility of individual species, and may theoretically affect departure load, mortality and phenology of individual birds (Weber et al 1999).…”