
Citation: | Yan Chen, Yong Zhang, Lei Cao, Willem F. de Boer, Anthony D. Fox. 2019: Wintering Swan Geese maximize energy intake through substrate foraging depth when feeding on buried Vallisneria natans tubers. Avian Research, 10(1): 6. DOI: 10.1186/s40657-019-0145-x |
Foraging theory predicts that animals select patches that offer the highest net rate of energy gain. Hence, prey distribution patterns and spatiotemporal heterogeneity play important roles in determining animal feeding patch selection. For waterfowl foraging on buried aquatic plant tubers, the distribution and biomass of these plant organs vary with depth in the substrate. Since excavation costs also increase with depth, the energy intake of the animals foraging on these plants is highly sediment depth dependent.
Here, using observations of Swan Geese (Anser cygnoides) foraging on Vallisneria natans tubers, we test our hypothesis that geese feeding on tubers buried at intermediate sediment depth maximize their daily energy intake because of the interaction between tuber size and abundance with depth. To do this, we measured the distribution patterns of buried Vallisneria tubers under both undisturbed conditions and post-exploitation by geese (i.e. giving-up conditions). We investigated the relationship between tuber size and burial depth, and total tuber biomass within each sediment layer in undisturbed and exploited plots. Finally, we compared modelled Swan Goose daily energy intake feeding on Vallisneria tubers buried at different sediment layers (1-10, 11-20 and 21-30 cm below the surface).
Dry weight of Vallisneria tubers linearly increased with burial depth, while average total dry weight density of tubers showed a unimodal relationship, peaking at intermediate levels. Not surprisingly, Swan Geese foraged most intensively on tubers buried at intermediate sediment depths, where they maximize their daily energy intake. Our results support our hypothesis that Swan Geese feeding on tubers at intermediate depths maximize their daily energy intake.
Our study is the first to quantify foraging strategies of Swan Geese during the wintering period, emphasizing the importance of plant traits on foraging selection of belowground foragers.
The authors regret that Fig. 1 and its caption should be replaced as below.
In addition, the last sentence of the third paragraph of section "3.1. Policy and administration" should be:
To improve the conservation of key waterbird habitats in the Yellow Sea region, which have high conservation priority for migratory birds in the EAAF, coastal wetlands in Yancheng, Jiangsu Province have been inscribed as UNESCO World Heritage Site, "Migratory bird sanctuaries along the coast of the Yellow Sea‒Bohai Gulf of China (Phase Ⅰ)", in 2019 (Fig. 1; World Heritage Committee, 2019), and 11 sites have been included in the list of Phase Ⅱ applications.
The authors would like to apologise for any inconvenience caused.
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