Seasonal changes in the water bird community in Lake Inba: Influence of floating-leaved macrophytes on habitat selection

The abundance of the floating-leaved macrophytes, especially Trapa spp., has increased in many eutrophic lakes, butits effects on waterbirds is not clear. By covering the water surface with their floating-leaves, these macrophytes exert effects that differ from those of submerged macrophytes. In this study, we investigated seasonal changes in the species composition and habitat selection of the waterbird community in the shallow, eutrophic Lake Inba in relation to the presence/absence of native floating-leaved macrophytes (Trapa spp.). The results indicated higher abundances of the eastern spot-billed duck (Anas zonorhyncha), the little grebe (Tachybaptus ruficollis), the great egret (Egretta alba), theintermediate egret (Egretta intermedia), and the Eurasian coot (Fulica atra) in Trapa beds, whereas the great cormorant Phalacrocorax carbo was more abundant in the open water without macrophytes. Both great egrets and intermediate egrets seemed to actively choose the Trapa beds as a feeding habitat that allowed them to catch the small fish swimming beneath these plants. Eurasian coots utilized Trapa spp. as food directly, by grazing on its fruits and leaves. Little grebes selected Trapa beds for nesting, especially when their flock size was larger. Conversely, Trapa beds prevented the foraging behavior of great cormorants. In Lake Inba, with its suddenly deep shoreline and lack of shallow areas, there are few potential feeding habitats for waterbirds in the littoral zones. Therefore, Trapa beds might provide an alternative habitat for these species, thus serving as an important ecotone between terrestrial and aquatic ecosystems.